diff --git a/.editorconfig b/.editorconfig
index 9277f564..85b86c30 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -8,7 +8,7 @@ indent_style = space
 insert_final_newline = true
 trim_trailing_whitespace = true
 
-[*.{cpp,h,hpp,py}]
+[*.{cpp,cppm,h,hpp,py}]
 indent_size = 4
 indent_style = space
 
diff --git a/.gitattributes b/.gitattributes
index 03c7c73e..c1d7c77d 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -22,5 +22,6 @@ Doxyfile text eol=lf
 *.c     text diff=c
 *.cc    text diff=cpp
 *.cpp   text diff=cpp
+*.cppm  text diff=cpp
 *.h     text diff=cpp
 *.hpp   text diff=cpp
diff --git a/.github/workflows/test-ubuntu.yml b/.github/workflows/test-ubuntu.yml
index 2073d76b..938cc3dc 100644
--- a/.github/workflows/test-ubuntu.yml
+++ b/.github/workflows/test-ubuntu.yml
@@ -14,6 +14,13 @@ jobs:
     strategy:
       matrix:
         include:
+          - name: clang++-16 C++20 module
+            os: ubuntu-24.04
+            cxx_compiler: clang++-16
+            cxx_standard: 20
+            cmake_options: "-G Ninja -DUPA_MODULE=ON -DCMAKE_CXX_FLAGS=-stdlib=libc++"
+            install: "libc++-16-dev libc++abi-16-dev"
+
           - name: clang++ C++20 shared-lib
             os: ubuntu-latest
             cxx_compiler: clang++
@@ -137,6 +144,12 @@ jobs:
             cmake_options: "-DUPA_BUILD_EXAMPLES=ON -DBUILD_SHARED_LIBS=ON"
             install_cmake: true
 
+          - name: g++-15 C++20 module
+            container: gcc:15
+            cxx_standard: 20
+            cmake_options: "-G Ninja -DUPA_MODULE=ON"
+            install_cmake: true
+
     steps:
     - name: install
       if: ${{ matrix.install_script }}
diff --git a/.github/workflows/test-windows.yml b/.github/workflows/test-windows.yml
index 6a6dc7ce..456f4ad7 100644
--- a/.github/workflows/test-windows.yml
+++ b/.github/workflows/test-windows.yml
@@ -56,6 +56,12 @@ jobs:
             cxx_standard: 20
             cmake_options: "-T ClangCL"
 
+          - name: VS 2026 C++20 module
+            os: windows-2025-vs2026
+            generator: "Visual Studio 18 2026"
+            cxx_standard: 20
+            cmake_options: "-DUPA_MODULE=ON"
+
     steps:
     - uses: actions/checkout@v6
     - name: get dependencies
diff --git a/CMakeLists.txt b/CMakeLists.txt
index c927c035..fd951eec 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 # add_link_options() requires 3.13
-cmake_minimum_required(VERSION 3.13)
+cmake_minimum_required(VERSION 3.13...3.28.2)
 
 # https://cmake.org/cmake/help/latest/policy/CMP0074.html
 if(POLICY CMP0074)
@@ -31,11 +31,6 @@ set(upa_export_name url)
 # to create the library filename
 set(upa_lib_target upa_url)
 
-if (NOT CMAKE_CXX_STANDARD)
-  set(CMAKE_CXX_STANDARD 17)
-  set(CMAKE_CXX_STANDARD_REQUIRED ON)
-endif()
-
 # Is the Upa URL a top-level project?
 if (NOT DEFINED UPA_MAIN_PROJECT)
   set(UPA_MAIN_PROJECT OFF)
@@ -53,13 +48,21 @@ option(UPA_BUILD_EXTRACTED "Build Upa URL examples extracted from the docs." OFF
 option(UPA_INSTALL "Generate the install target." ON)
 # library options
 option(UPA_AMALGAMATED "Use amalgamated URL library source." OFF)
+option(UPA_MODULE "Build a C++ module library." OFF)
 # tests build options
+option(UPA_MODULE_TESTS "Build C++ module tests." ${UPA_BUILD_TESTS})
 option(UPA_TEST_URL_FOR_QT "Build tests with Qt strings" OFF)
 option(UPA_TEST_COVERAGE "Build tests with code coverage reporting" OFF)
 option(UPA_TEST_COVERAGE_CLANG "Build tests with Clang source-based code coverage" OFF)
 option(UPA_TEST_SANITIZER "Build tests with Clang sanitizer" OFF)
 option(UPA_TEST_VALGRIND "Run tests with Valgrind" OFF)
 
+# C++ standard
+if (NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_CXX_STANDARD_REQUIRED ON)
+endif()
+
 # AFL, Honggfuzz, or Clang libFuzzer
 if (UPA_BUILD_FUZZER)
   set(UPA_BUILD_TESTS OFF)
@@ -117,6 +120,28 @@ endif()
 
 include_directories(deps)
 
+# The common setup for library targets
+function (configure_library_target lib_target export_name)
+  target_include_directories(${lib_target} PUBLIC
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+    $<INSTALL_INTERFACE:include>)
+
+  if (BUILD_SHARED_LIBS)
+    target_compile_definitions(${lib_target} PRIVATE UPA_LIB_EXPORT
+      INTERFACE UPA_LIB_IMPORT)
+    set_target_properties(${lib_target} PROPERTIES
+      VERSION ${UPA_URL_VERSION}
+      SOVERSION ${UPA_URL_SOVERSION}
+      CXX_VISIBILITY_PRESET hidden
+      VISIBILITY_INLINES_HIDDEN ON)
+  endif()
+
+  # Alias target for the library
+  add_library(upa::${export_name} ALIAS ${lib_target})
+  set_target_properties(${lib_target} PROPERTIES
+    EXPORT_NAME ${export_name})
+endfunction()
+
 # Is the Upa URL library needed?
 if (UPA_BUILD_TESTS OR UPA_BUILD_BENCH OR UPA_BUILD_FUZZER OR UPA_BUILD_EXAMPLES OR
     UPA_BUILD_EXTRACTED OR UPA_INSTALL)
@@ -137,28 +162,30 @@ if (UPA_BUILD_TESTS OR UPA_BUILD_BENCH OR UPA_BUILD_FUZZER OR UPA_BUILD_EXAMPLES
       src/url_search_params.cpp
       src/url_utf.cpp
       src/urlpattern.cpp)
-    target_include_directories(${upa_lib_target} PUBLIC
-      $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-      $<INSTALL_INTERFACE:include>)
+    configure_library_target(${upa_lib_target} ${upa_export_name})
   endif()
-  if (BUILD_SHARED_LIBS)
-    target_compile_definitions(${upa_lib_target} PRIVATE UPA_LIB_EXPORT
-      INTERFACE UPA_LIB_IMPORT)
-    set_target_properties(${upa_lib_target} PROPERTIES
-      VERSION ${UPA_URL_VERSION}
-      SOVERSION ${UPA_URL_SOVERSION}
-      CXX_VISIBILITY_PRESET hidden
-      VISIBILITY_INLINES_HIDDEN ON)
-  endif ()
-  # Alias target for the library
-  add_library(upa::${upa_export_name} ALIAS ${upa_lib_target})
-  set_target_properties(${upa_lib_target} PROPERTIES
-    EXPORT_NAME ${upa_export_name})
   # GCC 8 requires linking with stdc++fs to use std::filesystem
   target_link_libraries(${upa_lib_target} PRIVATE
     $<$<AND:$<CXX_COMPILER_ID:GNU>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,9.0>>:stdc++fs>)
 endif()
 
+if (UPA_MODULE)
+  set(CMAKE_CXX_EXTENSIONS OFF)
+
+  add_library(upa_url_module)
+  target_sources(upa_url_module
+    PRIVATE
+      src/module/upa.url.cpp
+    PUBLIC FILE_SET CXX_MODULES
+      BASE_DIRS
+        src/module
+      FILES
+        src/module/upa.url.cppm)
+  target_compile_features(upa_url_module
+    PUBLIC cxx_std_20)
+  configure_library_target(upa_url_module ${upa_export_name}-module)
+endif()
+
 # Test targets
 
 if (UPA_BUILD_TESTS)
@@ -216,6 +243,24 @@ if (UPA_BUILD_TESTS)
   endforeach()
 endif()
 
+if (UPA_MODULE AND UPA_MODULE_TESTS)
+  enable_testing()
+
+  set(test_files
+    test/test-module.cpp
+  )
+  foreach(file ${test_files})
+    get_filename_component(test_name ${file} NAME_WE)
+
+    add_executable(${test_name} ${file})
+    target_link_libraries(${test_name} upa_url_module)
+
+    add_test(NAME ${test_name}
+      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/test
+      COMMAND ${CMAKE_CURRENT_BINARY_DIR}/${test_name})
+  endforeach()
+endif()
+
 # Benchmark targets
 
 if (UPA_BUILD_BENCH)
@@ -267,11 +312,25 @@ if (UPA_INSTALL AND NOT UPA_AMALGAMATED)
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
   )
 
+  set(upa_install_targets ${upa_lib_target})
+  if (UPA_MODULE)
+    list(APPEND upa_install_targets upa_url_module)
+    set(upa_install_file_set
+      FILE_SET CXX_MODULES
+        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${upa_lib_name}/src)
+    set(upa_install_modules_dir
+      CXX_MODULES_DIRECTORY .)
+    install(
+      FILES src/module/upa.url.h
+      DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${upa_lib_name}/src)
+  endif()
+
   install(
-    TARGETS ${upa_lib_target}
+    TARGETS ${upa_install_targets}
     EXPORT ${upa_lib_target}-targets
     DESTINATION ${CMAKE_INSTALL_LIBDIR}
     RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+    ${upa_install_file_set}
   )
 
   install(
@@ -279,6 +338,7 @@ if (UPA_INSTALL AND NOT UPA_AMALGAMATED)
     FILE ${upa_lib_name}-targets.cmake
     NAMESPACE upa::
     DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${upa_lib_name}
+    ${upa_install_modules_dir}
   )
 
   # generate the config file that includes the exports
diff --git a/Doxyfile b/Doxyfile
index 7dea9471..85ae866d 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -2606,7 +2606,9 @@ PREDEFINED             =
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
 EXPAND_AS_DEFINED      = UPA_CONSTEXPR_20 UPA_CONSTEXPR_23 \
-                         UPA_LIFETIMEBOUND
+                         UPA_EXPORT UPA_EXPORT_BEGIN UPA_EXPORT_END \
+                         UPA_LIFETIMEBOUND \
+                         UPA_SO_VISIBLE
 
 # If the SKIP_FUNCTION_MACROS tag is set to YES then Doxygen's preprocessor will
 # remove all references to function-like macros that are alone on a line, have
diff --git a/include/upa/buffer.h b/include/upa/buffer.h
index 2d5ceeeb..546f40be 100644
--- a/include/upa/buffer.h
+++ b/include/upa/buffer.h
@@ -12,11 +12,13 @@
 
 #include "config.h"
 
-#include <array>
-#include <cstddef>
-#include <memory>
-#include <stdexcept>
-#include <string>
+#ifndef UPA_MODULE
+# include <array>
+# include <cstddef>
+# include <memory>
+# include <stdexcept>
+# include <string>
+#endif // UPA_MODULE
 
 namespace upa {
 
diff --git a/include/upa/config.h b/include/upa/config.h
index 5b71f67f..f2d926be 100644
--- a/include/upa/config.h
+++ b/include/upa/config.h
@@ -6,9 +6,11 @@
 #ifndef UPA_CONFIG_H
 #define UPA_CONFIG_H
 
-#if __has_include(<version>)
-# include <version> // IWYU pragma: export
-#endif
+#ifndef UPA_MODULE
+# if __has_include(<version>)
+#  include <version> // IWYU pragma: export
+# endif
+#endif // UPA_MODULE
 
 // Macros for compilers that support the C++20 or later standard
 // https://devblogs.microsoft.com/cppblog/msvc-now-correctly-reports-__cplusplus/
@@ -38,10 +40,24 @@
 # elif defined(__clang__) || defined(__GNUC__)
 #  define UPA_API __attribute__((visibility ("default")))
 # endif
+# if defined(__clang__) || defined(__GNUC__)
+#  define UPA_SO_VISIBLE __attribute__((visibility ("default")))
+# endif
 #endif
 #ifndef UPA_API
 # define UPA_API
 #endif
+#ifndef UPA_SO_VISIBLE
+# define UPA_SO_VISIBLE
+#endif
+
+// The following macros have values when the library is compiled as a module
+
+#ifndef UPA_EXPORT
+# define UPA_EXPORT
+# define UPA_EXPORT_BEGIN
+# define UPA_EXPORT_END
+#endif
 
 // Attributes
 
diff --git a/include/upa/public_suffix_list.h b/include/upa/public_suffix_list.h
index 4048cce2..44a3c9c6 100644
--- a/include/upa/public_suffix_list.h
+++ b/include/upa/public_suffix_list.h
@@ -1,4 +1,4 @@
-// Copyright 2024-2025 Rimas Misevičius
+// Copyright 2024-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
@@ -6,20 +6,25 @@
 #define UPA_PUBLIC_SUFFIX_LIST_H
 
 #include "url.h"
-#include <cstddef>
-#include <cstdint>
-#include <filesystem>
-#include <fstream>
-#include <ios>
-#include <istream>
-#include <memory>
-#include <string>
-#include <string_view>
-#include <unordered_map>
-#include <utility>
+
+#ifndef UPA_MODULE
+# include <cstddef>
+# include <cstdint>
+# include <filesystem>
+# include <fstream>
+# include <ios>
+# include <istream>
+# include <memory>
+# include <string>
+# include <string_view>
+# include <unordered_map>
+# include <utility>
+#endif // UPA_MODULE
 
 namespace upa {
 
+UPA_EXPORT_BEGIN
+
 /// @brief Get label position in hostname by it's index
 ///
 /// The label separator can be any of the following characters: U+002E (.),
@@ -135,7 +140,7 @@ class public_suffix_list {
     ///
     /// @param[in] filename the path to the Public Suffix List file
     /// @return true if the Public Suffix List was loaded successfully
-    bool load(const std::filesystem::path& filename) {
+    inline bool load(const std::filesystem::path& filename) {
         std::ifstream finp(filename, std::ios::in | std::ios::binary);
         return finp && load(finp);
     }
@@ -195,7 +200,7 @@ class public_suffix_list {
     /// @param[in] opt options
     /// @return public suffix or registrable domain (depends on @p opt value)
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    [[nodiscard]] std::string get_suffix(const StrT& str_host,
+    [[nodiscard]] inline std::string get_suffix(const StrT& str_host,
         option opt = option::public_suffix) const {
         try {
             return std::string{ get_suffix_view(
@@ -215,7 +220,7 @@ class public_suffix_list {
     /// @param[in] url the @ref url object
     /// @param[in] opt options
     /// @return information in the public_suffix_list::result type struct
-    [[nodiscard]] result get_suffix_info(const url& url,
+    [[nodiscard]] inline result get_suffix_info(const url& url,
         option opt = option::public_suffix) const {
         if (url.host_type() == HostType::Domain)
             return get_host_suffix_info(url.hostname(), opt);
@@ -230,7 +235,7 @@ class public_suffix_list {
     /// @param[in] host the url_host object
     /// @param[in] opt options
     /// @return information in the public_suffix_list::result type struct
-    [[nodiscard]] result get_suffix_info(const url_host& host,
+    [[nodiscard]] inline result get_suffix_info(const url_host& host,
         option opt = option::public_suffix) const {
         if (host.type() == HostType::Domain)
             return get_host_suffix_info(host.name(), opt);
@@ -246,7 +251,7 @@ class public_suffix_list {
     /// @param[in] opt options
     /// @return information in the public_suffix_list::result type struct
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    [[nodiscard]] result get_suffix_info(const StrT& str_host,
+    [[nodiscard]] inline result get_suffix_info(const StrT& str_host,
         option opt = option::public_suffix) const {
         try {
             auto res = get_suffix_info(upa::url_host{ str_host }, opt);
@@ -273,7 +278,7 @@ class public_suffix_list {
     /// @param[in] url the @ref url object
     /// @param[in] opt options
     /// @return public suffix or registrable domain (depends on @p opt value)
-    [[nodiscard]] std::string_view get_suffix_view(const url& url UPA_LIFETIMEBOUND,
+    [[nodiscard]] inline std::string_view get_suffix_view(const url& url UPA_LIFETIMEBOUND,
         option opt = option::public_suffix) const {
         if (url.host_type() == HostType::Domain)
             return get_host_suffix_view(url.hostname(), opt);
@@ -295,7 +300,7 @@ class public_suffix_list {
     /// @param[in] host the url_host object
     /// @param[in] opt options
     /// @return public suffix or registrable domain (depends on @p opt value)
-    [[nodiscard]] std::string_view get_suffix_view(const url_host& host UPA_LIFETIMEBOUND,
+    [[nodiscard]] inline std::string_view get_suffix_view(const url_host& host UPA_LIFETIMEBOUND,
         option opt = option::public_suffix) const {
         if (host.type() == HostType::Domain)
             return get_host_suffix_view(host.name(), opt);
@@ -318,7 +323,7 @@ class public_suffix_list {
     /// @param[in] opt options
     /// @return public suffix or registrable domain (depends on @p opt value)
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    [[nodiscard]] auto get_suffix_view(const StrT& str_host, option opt = option::public_suffix) const
+    [[nodiscard]] inline auto get_suffix_view(const StrT& str_host, option opt = option::public_suffix) const
         -> std::basic_string_view<typename str_arg<str_arg_char_t<StrT>>::value_type> {
         try {
             const auto arg = make_str_arg(str_host);
@@ -351,7 +356,7 @@ class public_suffix_list {
 private:
     UPA_API result get_host_suffix_info(std::string_view hostname, option opt) const;
 
-    std::string_view get_host_suffix_view(std::string_view hostname, option opt) const {
+    inline std::string_view get_host_suffix_view(std::string_view hostname, option opt) const {
         const auto res = get_host_suffix_info(hostname, opt);
         if (res)
             return hostname.substr(res.first_label_pos);
@@ -366,9 +371,9 @@ class public_suffix_list {
             using hash_type = std::hash<std::string_view>;
             using is_transparent = void;
 
-            std::size_t operator()(const char* str) const { return hash_type{}(str); }
-            std::size_t operator()(std::string_view str) const { return hash_type{}(str); }
-            std::size_t operator()(std::string const& str) const { return hash_type{}(str); }
+            inline std::size_t operator()(const char* str) const { return hash_type{}(str); }
+            inline std::size_t operator()(std::string_view str) const { return hash_type{}(str); }
+            inline std::size_t operator()(std::string const& str) const { return hash_type{}(str); }
         };
         using map_type = std::unordered_map<std::string, label_item, string_hash, std::equal_to<>>;
 #else
@@ -378,7 +383,7 @@ class public_suffix_list {
         std::uint8_t code = 0;
         std::unique_ptr<map_type> children;
 
-        bool operator==(const label_item& b) const {
+        inline bool operator==(const label_item& b) const {
             return code == b.code && (
                 (!children && !b.children) ||
                 (children && b.children && *children == *b.children));
@@ -395,6 +400,9 @@ struct enable_bitmask_operators<upa::public_suffix_list::option>
     : public std::true_type {};
 
 } // namespace idna
+
+UPA_EXPORT_END
+
 } // namespace upa
 
 #endif // UPA_PUBLIC_SUFFIX_LIST_H
diff --git a/include/upa/regex_engine_srell.h b/include/upa/regex_engine_srell.h
index 072fdb50..f4a20149 100644
--- a/include/upa/regex_engine_srell.h
+++ b/include/upa/regex_engine_srell.h
@@ -1,4 +1,4 @@
-// Copyright 2025 Rimas Misevičius
+// Copyright 2025-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
@@ -28,10 +28,10 @@ class regex_engine_srell {
 public:
     class result {
     public:
-        std::size_t size() const {
+        inline std::size_t size() const {
             return arr_.size();
         }
-        std::optional<std::string> get(std::size_t ind, std::string_view) const {
+        inline std::optional<std::string> get(std::size_t ind, std::string_view) const {
             const auto& res = arr_[ind];
             if (res.matched)
                 return std::string{ res.first, res.second };
@@ -42,7 +42,7 @@ class regex_engine_srell {
         friend class regex_engine_srell;
     };
 
-    bool init(std::string_view regex_str, bool ignore_case) {
+    inline bool init(std::string_view regex_str, bool ignore_case) {
         // 4. If options's ignore case is true then set flags to "vi".
         // 5. Otherwise set flags to "v"
         const auto commonflags = srell::regex::ECMAScript | srell::regex::vmode |
@@ -53,10 +53,10 @@ class regex_engine_srell {
         return re_.assign(regex_str.data(), regex_str.length(), flag).ecode() == 0;
     }
 
-    bool exec(std::string_view input, result& res) const {
+    inline bool exec(std::string_view input, result& res) const {
         return srell::regex_match(input.begin(), input.end(), res.arr_, re_);
     }
-    bool test(std::string_view input) const {
+    inline bool test(std::string_view input) const {
         return srell::regex_match(input.begin(), input.end(), re_);
     }
 
diff --git a/include/upa/regex_engine_std.h b/include/upa/regex_engine_std.h
index 97ff2bb8..41e18a7b 100644
--- a/include/upa/regex_engine_std.h
+++ b/include/upa/regex_engine_std.h
@@ -1,4 +1,4 @@
-// Copyright 2025 Rimas Misevičius
+// Copyright 2025-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
@@ -25,10 +25,10 @@ class regex_engine_std {
 public:
     class result {
     public:
-        std::size_t size() const {
+        inline std::size_t size() const {
             return arr_.size();
         }
-        std::optional<std::string> get(std::size_t ind, std::string_view) const {
+        inline std::optional<std::string> get(std::size_t ind, std::string_view) const {
             const auto& res = arr_[ind];
             if (res.matched)
                 return std::string{ res.first, res.second };
@@ -39,7 +39,7 @@ class regex_engine_std {
         friend class regex_engine_std;
     };
 
-    bool init(std::string_view regex_str, bool ignore_case) {
+    inline bool init(std::string_view regex_str, bool ignore_case) {
         // 4. If options's ignore case is true then set flags to "vi".
         // 5. Otherwise set flags to "v"
         // Note that the std::regex does not have the "v" flag.
@@ -55,10 +55,10 @@ class regex_engine_std {
         }
     }
 
-    bool exec(std::string_view input, result& res) const {
+    inline bool exec(std::string_view input, result& res) const {
         return std::regex_match(input.begin(), input.end(), res.arr_, re_);
     }
-    bool test(std::string_view input) const {
+    inline bool test(std::string_view input) const {
         return std::regex_match(input.begin(), input.end(), re_);
     }
 
diff --git a/include/upa/str_arg.h b/include/upa/str_arg.h
index ac68dd7a..d18054db 100644
--- a/include/upa/str_arg.h
+++ b/include/upa/str_arg.h
@@ -21,13 +21,16 @@ inline void procfn(const StrT& str) {
 #include "config.h"
 #include "url_utf.h"
 #include "util.h"
-#include <cassert>
-#include <cstddef>
-#include <optional>
-#include <string>
-#include <string_view>
-#include <type_traits>
-#include <utility>
+
+#ifndef UPA_MODULE
+# include <cassert>
+# include <cstddef>
+# include <optional>
+# include <string>
+# include <string_view>
+# include <type_traits>
+# include <utility>
+#endif // UPA_MODULE
 
 namespace upa {
 
@@ -35,6 +38,8 @@ namespace upa {
 
 using string_view [[deprecated("Use std::string_view instead.")]] = std::string_view;
 
+UPA_EXPORT_BEGIN
+
 // Supported char and size types
 
 template<class CharT>
@@ -134,6 +139,8 @@ using remove_cvptr_t = std::remove_cv_t<std::remove_pointer_t<T>>;
 template<class T>
 using remove_cvref_t = std::remove_cv_t<std::remove_reference_t<T>>;
 
+UPA_EXPORT_END
+
 namespace detail {
 
 // Check that StrT has data() and size() members of supported types
@@ -217,6 +224,7 @@ struct str_arg_char_default<StrT, std::enable_if_t<
 
 } // namespace detail
 
+UPA_EXPORT_BEGIN
 
 // Requirements for string arguments
 
@@ -241,6 +249,7 @@ struct str_arg_char<str_arg<CharT>> {
     }
 };
 
+UPA_EXPORT_END
 
 // String arguments helper types
 
@@ -291,6 +300,7 @@ using enable_if_str_arg_to_charW_t = std::enable_if_t<
     is_charW_type_v<str_arg_char_t<StrT>>,
     int>;
 
+UPA_EXPORT_BEGIN
 
 UPA_CONSTEXPR_20 std::string&& make_string(std::string&& str) {
     return std::move(str);
@@ -308,6 +318,7 @@ inline std::string make_string(const StrT& str) {
     return url_utf::to_utf8_string(inp.begin(), inp.end());
 }
 
+UPA_EXPORT_END
 
 // Support for optional string arguments
 
@@ -326,7 +337,11 @@ inline constexpr bool is_just_optional_v<std::optional<T>> = true;
 
 } // namespace detail
 
-// helpers for optional string arguments
+// Helpers for optional string arguments
+
+// The upa::nullopt can be used instead of std::nullopt to provide a workaround for the MSVC bug
+// https://developercommunity.visualstudio.com/t/The-C2039:-nullopt:-is-not-a-member-o/11099621
+UPA_EXPORT inline constexpr auto nullopt = std::nullopt;
 
 template<class OptStrT>
 using enable_if_optional_str_arg_t = std::enable_if_t<
diff --git a/include/upa/url.h b/include/upa/url.h
index cafbeb4d..9975ce21 100644
--- a/include/upa/url.h
+++ b/include/upa/url.h
@@ -26,20 +26,23 @@
 #include "url_search_params.h"  // IWYU pragma: export
 #include "url_version.h"        // IWYU pragma: export
 #include "util.h"
-#include <algorithm>
-#include <array>
-#include <cassert>
-#include <cstddef>
-#include <cstdint> // uint8_t
-#include <filesystem>
-#include <functional> // std::hash
-#include <iterator>
-#include <ostream>
-#include <string>
-#include <string_view>
-#include <type_traits>
-#include <utility>
-#include <vector>
+
+#ifndef UPA_MODULE
+# include <algorithm>
+# include <array>
+# include <cassert>
+# include <cstddef>
+# include <cstdint> // uint8_t
+# include <filesystem>
+# include <functional> // std::hash
+# include <iterator>
+# include <ostream>
+# include <string>
+# include <string_view>
+# include <type_traits>
+# include <utility>
+# include <vector>
+#endif // UPA_MODULE
 
 // not yet
 // #define UPA_URL_USE_ENCODING
@@ -71,6 +74,8 @@ inline constexpr const char* kBaseURLParseError = "Base URL parse error";
 
 } // namespace detail
 
+UPA_EXPORT_BEGIN
+
 /// @brief URL class
 ///
 /// Follows specification in
@@ -142,7 +147,7 @@ class url {
     /// @param[in] str_url URL string to parse
     /// @param[in] pbase   pointer to base URL, may be `nullptr`
     template <class T, enable_if_str_arg_t<T> = 0>
-    explicit url(const T& str_url, const url* pbase = nullptr)
+    inline explicit url(const T& str_url, const url* pbase = nullptr)
         : url{ str_url, pbase, detail::kURLParseError }
     {}
 
@@ -153,7 +158,7 @@ class url {
     /// @param[in] str_url URL string to parse
     /// @param[in] base    base URL
     template <class T, enable_if_str_arg_t<T> = 0>
-    explicit url(const T& str_url, const url& base)
+    inline explicit url(const T& str_url, const url& base)
         : url{ str_url, &base, detail::kURLParseError }
     {}
 
@@ -164,7 +169,7 @@ class url {
     /// @param[in] str_url  URL string to parse
     /// @param[in] str_base base URL string
     template <class T, class TB, enable_if_str_arg_t<T> = 0, enable_if_str_arg_t<TB> = 0>
-    explicit url(const T& str_url, const TB& str_base)
+    inline explicit url(const T& str_url, const TB& str_base)
         : url{ str_url, url{ str_base, nullptr, detail::kBaseURLParseError } }
     {}
 
@@ -191,7 +196,7 @@ class url {
     /// @param[in] base    pointer to base URL, may be nullptr
     /// @return error code (@a validation_errc::ok on success)
     template <class T, enable_if_str_arg_t<T> = 0>
-    validation_errc parse(const T& str_url, const url* base = nullptr) {
+    inline validation_errc parse(const T& str_url, const url* base = nullptr) {
         const auto inp = make_str_arg(str_url);
         return do_parse(inp.begin(), inp.end(), base);
     }
@@ -202,7 +207,7 @@ class url {
     /// @param[in] base    base URL
     /// @return error code (@a validation_errc::ok on success)
     template <class T, enable_if_str_arg_t<T> = 0>
-    validation_errc parse(const T& str_url, const url& base) {
+    inline validation_errc parse(const T& str_url, const url& base) {
         return parse(str_url, &base);
     }
 
@@ -212,7 +217,7 @@ class url {
     /// @param[in] str_base base URL string
     /// @return error code (@a validation_errc::ok on success)
     template <class T, class TB, enable_if_str_arg_t<T> = 0, enable_if_str_arg_t<TB> = 0>
-    validation_errc parse(const T& str_url, const TB& str_base) {
+    inline validation_errc parse(const T& str_url, const TB& str_base) {
         upa::url base;
         const auto res = base.parse(str_base, nullptr);
         return res == validation_errc::ok
@@ -229,7 +234,7 @@ class url {
     /// @param[in] pbase   pointer to base URL, may be `nullptr`
     /// @return true if given @a str_url can be parsed against @a *pbase
     template <class T, enable_if_str_arg_t<T> = 0>
-    [[nodiscard]] static bool can_parse(const T& str_url, const url* pbase = nullptr) {
+    [[nodiscard]] static inline bool can_parse(const T& str_url, const url* pbase = nullptr) {
         upa::url url;
         return url.for_can_parse(str_url, pbase) == validation_errc::ok;
     }
@@ -243,7 +248,7 @@ class url {
     /// @param[in] base    base URL
     /// @return true if given @a str_url can be parsed against base URL
     template <class T, enable_if_str_arg_t<T> = 0>
-    [[nodiscard]] static bool can_parse(const T& str_url, const url& base) {
+    [[nodiscard]] static inline bool can_parse(const T& str_url, const url& base) {
         return can_parse(str_url, &base);
     }
 
@@ -257,7 +262,7 @@ class url {
     /// @param[in] str_base base URL string
     /// @return true if given @a str_url can be parsed against @a str_base URL string
     template <class T, class TB, enable_if_str_arg_t<T> = 0, enable_if_str_arg_t<TB> = 0>
-    [[nodiscard]] static bool can_parse(const T& str_url, const TB& str_base) {
+    [[nodiscard]] static inline bool can_parse(const T& str_url, const TB& str_base) {
         upa::url base;
         return
             base.for_can_parse(str_base, nullptr) == validation_errc::ok &&
@@ -277,7 +282,7 @@ class url {
     bool href(const StrT& str);
     /// Equivalent to @link href(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_href(const StrT& str) { return href(str); }
+    inline bool set_href(const StrT& str) { return href(str); }
 
     /// @brief The protocol setter
     ///
@@ -290,7 +295,7 @@ class url {
     bool protocol(const StrT& str);
     /// Equivalent to @link protocol(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_protocol(const StrT& str) { return protocol(str); }
+    inline bool set_protocol(const StrT& str) { return protocol(str); }
 
     /// @brief The username setter
     ///
@@ -303,7 +308,7 @@ class url {
     bool username(const StrT& str);
     /// Equivalent to @link username(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_username(const StrT& str) { return username(str); }
+    inline bool set_username(const StrT& str) { return username(str); }
 
     /// @brief The password setter
     ///
@@ -316,7 +321,7 @@ class url {
     bool password(const StrT& str);
     /// Equivalent to @link password(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_password(const StrT& str) { return password(str); }
+    inline bool set_password(const StrT& str) { return password(str); }
 
     /// @brief The host setter
     ///
@@ -329,7 +334,7 @@ class url {
     bool host(const StrT& str);
     /// Equivalent to @link host(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_host(const StrT& str) { return host(str); }
+    inline bool set_host(const StrT& str) { return host(str); }
 
     /// @brief The hostname setter
     ///
@@ -342,7 +347,7 @@ class url {
     bool hostname(const StrT& str);
     /// Equivalent to @link hostname(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_hostname(const StrT& str) { return hostname(str); }
+    inline bool set_hostname(const StrT& str) { return hostname(str); }
 
     /// @brief The port setter
     ///
@@ -355,7 +360,7 @@ class url {
     bool port(const StrT& str);
     /// Equivalent to @link port(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_port(const StrT& str) { return port(str); }
+    inline bool set_port(const StrT& str) { return port(str); }
 
     /// @brief The pathname setter
     ///
@@ -368,7 +373,7 @@ class url {
     bool pathname(const StrT& str);
     /// Equivalent to @link pathname(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_pathname(const StrT& str) { return pathname(str); }
+    inline bool set_pathname(const StrT& str) { return pathname(str); }
 
     /// @brief The search setter
     ///
@@ -381,7 +386,7 @@ class url {
     bool search(const StrT& str);
     /// Equivalent to @link search(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_search(const StrT& str) { return search(str); }
+    inline bool set_search(const StrT& str) { return search(str); }
 
     /// @brief The hash setter
     ///
@@ -394,7 +399,7 @@ class url {
     bool hash(const StrT& str);
     /// Equivalent to @link hash(const StrT& str) @endlink
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    bool set_hash(const StrT& str) { return hash(str); }
+    inline bool set_hash(const StrT& str) { return hash(str); }
 
     // Getters
 
@@ -405,7 +410,7 @@ class url {
     /// @return serialized URL
     [[nodiscard]] std::string_view href() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link href() const @endlink
-    [[nodiscard]] std::string_view get_href() const UPA_LIFETIMEBOUND { return href(); }
+    [[nodiscard]] inline std::string_view get_href() const UPA_LIFETIMEBOUND { return href(); }
 
     /// @brief The origin getter
     ///
@@ -424,7 +429,7 @@ class url {
     /// @return URL's scheme, followed by U+003A (:)
     [[nodiscard]] std::string_view protocol() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link protocol() const @endlink
-    [[nodiscard]] std::string_view get_protocol() const UPA_LIFETIMEBOUND { return protocol(); }
+    [[nodiscard]] inline std::string_view get_protocol() const UPA_LIFETIMEBOUND { return protocol(); }
 
     /// @brief The username getter
     ///
@@ -433,7 +438,7 @@ class url {
     /// @return URL’s username
     [[nodiscard]] std::string_view username() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link username() const @endlink
-    [[nodiscard]] std::string_view get_username() const UPA_LIFETIMEBOUND { return username(); }
+    [[nodiscard]] inline std::string_view get_username() const UPA_LIFETIMEBOUND { return username(); }
 
     /// @brief The password getter
     ///
@@ -442,7 +447,7 @@ class url {
     /// @return URL’s password
     [[nodiscard]] std::string_view password() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link password() const @endlink
-    [[nodiscard]] std::string_view get_password() const UPA_LIFETIMEBOUND { return password(); }
+    [[nodiscard]] inline std::string_view get_password() const UPA_LIFETIMEBOUND { return password(); }
 
     /// @brief The host getter
     ///
@@ -451,7 +456,7 @@ class url {
     /// @return URL’s host, serialized, followed by U+003A (:) and URL’s port, serialized
     [[nodiscard]] std::string_view host() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link host() const @endlink
-    [[nodiscard]] std::string_view get_host() const UPA_LIFETIMEBOUND { return host(); }
+    [[nodiscard]] inline std::string_view get_host() const UPA_LIFETIMEBOUND { return host(); }
 
     /// @brief The hostname getter
     ///
@@ -460,7 +465,7 @@ class url {
     /// @return URL’s host, serialized
     [[nodiscard]] std::string_view hostname() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link hostname() const @endlink
-    [[nodiscard]] std::string_view get_hostname() const UPA_LIFETIMEBOUND { return hostname(); }
+    [[nodiscard]] inline std::string_view get_hostname() const UPA_LIFETIMEBOUND { return hostname(); }
 
     /// @brief The host_type getter
     ///
@@ -474,7 +479,7 @@ class url {
     /// @return URL’s port, serialized, if URL’s port is not null, otherwise empty string
     [[nodiscard]] std::string_view port() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link port() const @endlink
-    [[nodiscard]] std::string_view get_port() const UPA_LIFETIMEBOUND { return port(); }
+    [[nodiscard]] inline std::string_view get_port() const UPA_LIFETIMEBOUND { return port(); }
 
     /// @return URL’s port, converted to `int` value, if URL’s port is not null,
     ///   otherwise `-1`
@@ -490,7 +495,7 @@ class url {
     /// @return URL's path, serialized, followed by U+003F (?) and URL’s query
     [[nodiscard]] std::string_view path() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link path() const @endlink
-    [[nodiscard]] std::string_view get_path() const UPA_LIFETIMEBOUND { return path(); }
+    [[nodiscard]] inline std::string_view get_path() const UPA_LIFETIMEBOUND { return path(); }
 
     /// @brief The pathname getter
     ///
@@ -499,7 +504,7 @@ class url {
     /// @return URL’s path, serialized
     [[nodiscard]] std::string_view pathname() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link pathname() const @endlink
-    [[nodiscard]] std::string_view get_pathname() const UPA_LIFETIMEBOUND { return pathname(); }
+    [[nodiscard]] inline std::string_view get_pathname() const UPA_LIFETIMEBOUND { return pathname(); }
 
     /// @brief The search getter
     ///
@@ -508,7 +513,7 @@ class url {
     /// @return empty string or U+003F (?), followed by URL’s query
     [[nodiscard]] std::string_view search() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link search() const @endlink
-    [[nodiscard]] std::string_view get_search() const UPA_LIFETIMEBOUND { return search(); }
+    [[nodiscard]] inline std::string_view get_search() const UPA_LIFETIMEBOUND { return search(); }
 
     /// @brief The hash getter
     ///
@@ -517,7 +522,7 @@ class url {
     /// @return empty string or U+0023 (#), followed by URL’s fragment
     [[nodiscard]] std::string_view hash() const UPA_LIFETIMEBOUND;
     /// Equivalent to @link hash() const @endlink
-    [[nodiscard]] std::string_view get_hash() const UPA_LIFETIMEBOUND { return hash(); }
+    [[nodiscard]] inline std::string_view get_hash() const UPA_LIFETIMEBOUND { return hash(); }
 
     /// @brief The searchParams getter
     ///
@@ -670,21 +675,6 @@ class url {
         INITIAL_FLAGS = SCHEME_FLAG | USERNAME_FLAG | PASSWORD_FLAG | PATH_FLAG,
     };
 
-    // part flag masks
-    static constexpr unsigned kPartFlagMask[url::PART_COUNT] = {
-        SCHEME_FLAG,
-        0,  // SCHEME_SEP
-        USERNAME_FLAG,
-        PASSWORD_FLAG,
-        0,  // HOST_START
-        HOST_FLAG | HOST_TYPE_MASK,
-        PORT_FLAG,
-        0,  // PATH_PREFIX
-        PATH_FLAG | OPAQUE_PATH_FLAG,
-        QUERY_FLAG,
-        FRAGMENT_FLAG
-    };
-
     // parsing constructor
     template <class T, enable_if_str_arg_t<T> = 0>
     explicit url(const T& str_url, const url* base, const char* what_arg);
@@ -745,16 +735,17 @@ class url {
     friend class url_search_params;
 };
 
+UPA_EXPORT_END
 
 namespace detail {
 
-class url_serializer : public host_output {
+class UPA_SO_VISIBLE url_serializer : public host_output {
 public:
     url_serializer() = delete;
     url_serializer(const url_serializer&) = delete;
     url_serializer& operator=(const url_serializer&) = delete;
 
-    explicit url_serializer(url& dest_url, bool need_save = true)
+    inline explicit url_serializer(url& dest_url, bool need_save = true)
         : host_output(need_save)
         , url_(dest_url)
         , last_pt_(url::SCHEME)
@@ -762,16 +753,18 @@ class url_serializer : public host_output {
 
     ~url_serializer() override = default;
 
-    void new_url() {
+    inline void new_url() {
         if (!url_.empty())
             url_.clear();
     }
-    virtual void reserve(std::size_t new_cap) { util::reserve(url_.norm_url_, new_cap); }
+    inline virtual void reserve(std::size_t new_cap) {
+        util::reserve(url_.norm_url_, new_cap);
+    }
 
     // set data
-    void set_scheme(const url& src) { url_.set_scheme(src); }
-    void set_scheme(std::string_view str) { url_.set_scheme(str); }
-    void set_scheme(std::size_t scheme_length) { url_.set_scheme(scheme_length); }
+    inline void set_scheme(const url& src) { url_.set_scheme(src); }
+    inline void set_scheme(std::string_view str) { url_.set_scheme(str); }
+    inline void set_scheme(std::size_t scheme_length) { url_.set_scheme(scheme_length); }
 
     // set scheme
     virtual std::string& start_scheme();
@@ -782,7 +775,7 @@ class url_serializer : public host_output {
     virtual std::string& start_part(url::PartType new_pt);
     virtual void save_part();
 
-    virtual void clear_part(url::PartType /*pt*/) {}
+    inline virtual void clear_part(url::PartType /*pt*/) {}
 
     // set empty host
     void set_empty_host();
@@ -814,29 +807,29 @@ class url_serializer : public host_output {
     void append_parts(const url& src, url::PartType t1, url::PartType t2, PathOpFn pathOpFn = nullptr);
 
     // flags
-    void set_flag(const url::UrlFlag flag) { url_.set_flag(flag); }
-    void set_host_type(const HostType ht) { url_.set_host_type(ht); }
+    inline void set_flag(const url::UrlFlag flag) { url_.set_flag(flag); }
+    inline void set_host_type(const HostType ht) { url_.set_host_type(ht); }
     // IMPORTANT: has-an-opaque-path flag must be set before or just after
     // SCHEME set; because other part's serialization depends on this flag
-    void set_has_opaque_path() {
+    inline void set_has_opaque_path() {
         assert(last_pt_ == url::SCHEME);
         url_.set_has_opaque_path();
     }
 
     // get info
-    std::string_view get_part_view(url::PartType t) const { return url_.get_part_view(t); }
-    bool is_empty(const url::PartType t) const { return url_.is_empty(t); }
-    virtual bool is_empty_path() const {
+    inline std::string_view get_part_view(url::PartType t) const { return url_.get_part_view(t); }
+    inline bool is_empty(const url::PartType t) const { return url_.is_empty(t); }
+    inline virtual bool is_empty_path() const {
         assert(!url_.has_opaque_path());
         // path_segment_count_ has meaning only if path is a list (path isn't opaque)
         return url_.path_segment_count_ == 0;
     }
-    bool is_null(const url::PartType t) const noexcept { return url_.is_null(t); }
-    bool is_special_scheme() const noexcept { return url_.is_special_scheme(); }
-    bool is_file_scheme() const noexcept { return url_.is_file_scheme(); }
-    bool has_credentials() const { return url_.has_credentials(); }
-    const detail::scheme_info* scheme_inf() const noexcept { return url_.scheme_inf_; }
-    int port_int() const { return url_.port_int(); }
+    inline bool is_null(const url::PartType t) const noexcept { return url_.is_null(t); }
+    inline bool is_special_scheme() const noexcept { return url_.is_special_scheme(); }
+    inline bool is_file_scheme() const noexcept { return url_.is_file_scheme(); }
+    inline bool has_credentials() const { return url_.has_credentials(); }
+    inline const detail::scheme_info* scheme_inf() const noexcept { return url_.scheme_inf_; }
+    inline int port_int() const { return url_.port_int(); }
 
 protected:
     void adjust_path_prefix();
@@ -854,13 +847,13 @@ class url_serializer : public host_output {
 };
 
 
-class url_setter : public url_serializer {
+class UPA_SO_VISIBLE url_setter : public url_serializer {
 public:
     url_setter() = delete;
     url_setter(const url_setter&) = delete;
     url_setter& operator=(const url_setter&) = delete;
 
-    explicit url_setter(url& dest_url)
+    inline explicit url_setter(url& dest_url)
         : url_serializer(dest_url)
         , use_strp_(true)
         , curr_pt_(url::SCHEME)
@@ -936,7 +929,7 @@ class url_parser {
     };
 
     template <typename CharT>
-    static validation_errc url_parse(url_serializer& urls, const CharT* first, const CharT* last, const url* base, State state_override = not_set_state);
+    static validation_errc url_parse(url_serializer& urls, const CharT* first, const CharT* last, const url* base, State state_override);
 
     template <typename CharT>
     static validation_errc parse_host(url_serializer& urls, const CharT* first, const CharT* last);
@@ -1460,7 +1453,7 @@ inline validation_errc url::do_parse(const CharT* first, const CharT* last, cons
         detail::do_trim(first, last);
         //TODO-WARN: validation error if trimmed
 
-        return detail::url_parser::url_parse(urls, first, last, base);
+        return detail::url_parser::url_parse(urls, first, last, base, detail::url_parser::not_set_state);
     }();
     if (res == validation_errc::ok) {
         set_flag(VALID_FLAG);
@@ -1488,7 +1481,7 @@ validation_errc url::for_can_parse(const T& str_url, const url* base) {
         detail::do_trim(first, last);
         //TODO-WARN: validation error if trimmed
 
-        return detail::url_parser::url_parse(urls, first, last, base);
+        return detail::url_parser::url_parse(urls, first, last, base, detail::url_parser::not_set_state);
     }();
     if (res == validation_errc::ok)
         set_flag(VALID_FLAG);
@@ -2759,10 +2752,25 @@ inline void url_serializer::append_parts(const url& src, url::PartType t1, url::
         return t1;
     }();
 
+    // part flag masks
+    static constexpr unsigned kPartFlagMask[url::PART_COUNT] = {
+        url::SCHEME_FLAG,
+        0,  // SCHEME_SEP
+        url::USERNAME_FLAG,
+        url::PASSWORD_FLAG,
+        0,  // HOST_START
+        url::HOST_FLAG | url::HOST_TYPE_MASK,
+        url::PORT_FLAG,
+        0,  // PATH_PREFIX
+        url::PATH_FLAG | url::OPAQUE_PATH_FLAG,
+        url::QUERY_FLAG,
+        url::FRAGMENT_FLAG
+    };
+
     // copy flags; they can be used when copying / serializing url parts below
     unsigned mask = 0;
     for (int ind = t1; ind <= t2; ++ind) {
-        mask |= url::kPartFlagMask[ind];
+        mask |= kPartFlagMask[ind];
     }
     url_.flags_ = (url_.flags_ & ~mask) | (src.flags_ & mask);
 
@@ -3111,6 +3119,7 @@ constexpr bool has_dot_dot_segment(const CharT* first, const CharT* last, IsSlas
 
 } // namespace detail
 
+UPA_EXPORT_BEGIN
 
 // URL utilities (non-member functions)
 
@@ -3399,6 +3408,8 @@ inline bool check_version() {
         (static_cast<std::uint32_t>(UPA_URL_VERSION_NUM) & sover_mask);
 }
 
+UPA_EXPORT_END
+
 } // namespace upa
 
 
@@ -3407,7 +3418,7 @@ namespace std {
 /// @brief std::hash specialization for upa::url class
 template<>
 struct hash<upa::url> {
-    [[nodiscard]] std::size_t operator()(const upa::url& url) const noexcept {
+    [[nodiscard]] inline std::size_t operator()(const upa::url& url) const noexcept {
         return std::hash<std::string>{}(url.norm_url_);
     }
 };
diff --git a/include/upa/url_for_atl.h b/include/upa/url_for_atl.h
index 4df7032f..8ff6e06c 100644
--- a/include/upa/url_for_atl.h
+++ b/include/upa/url_for_atl.h
@@ -1,4 +1,4 @@
-// Copyright 2024 Rimas Misevičius
+// Copyright 2024-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 
@@ -23,7 +23,7 @@ template<class StrT>
 struct str_arg_char_for_atl {
     using type = typename StrT::XCHAR;
 
-    static str_arg<type> to_str_arg(const StrT& str) {
+    static inline str_arg<type> to_str_arg(const StrT& str) {
         return { str.GetString(), str.GetLength() };
     }
 };
diff --git a/include/upa/url_for_qt.h b/include/upa/url_for_qt.h
index 0dd967e8..673d5ccd 100644
--- a/include/upa/url_for_qt.h
+++ b/include/upa/url_for_qt.h
@@ -1,4 +1,4 @@
-// Copyright 2024-2025 Rimas Misevičius
+// Copyright 2024-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 
@@ -36,7 +36,7 @@ struct str_arg_char_for_qt {
         "StrT::value_type and CharT must be the same size");
     using type = CharT;
 
-    static str_arg<type> to_str_arg(const StrT& str) {
+    static inline str_arg<type> to_str_arg(const StrT& str) {
         return { str.data(), str.size() };
     }
 };
diff --git a/include/upa/url_host.h b/include/upa/url_host.h
index b64c382d..4ae19674 100644
--- a/include/upa/url_host.h
+++ b/include/upa/url_host.h
@@ -15,19 +15,22 @@
 #include "url_result.h"
 #include "url_utf.h"
 #include "util.h"
-#include <algorithm> // any_of
-#include <cassert>
-#include <cstdint> // uint16_t, uint32_t
-#include <string>
-#include <string_view>
-#include <type_traits>
+
+#ifndef UPA_MODULE
+# include <algorithm> // any_of
+# include <cassert>
+# include <cstdint> // uint16_t, uint32_t
+# include <string>
+# include <string_view>
+# include <type_traits>
+#endif // UPA_MODULE
 
 namespace upa {
 
 /// @brief Host representation
 ///
 /// See: https://url.spec.whatwg.org/#host-representation
-enum class HostType {
+UPA_EXPORT enum class HostType {
     Empty = 0, ///< **empty host** is the empty string
     Opaque,    ///< **opaque host** is a non-empty ASCII string used in a not special URL
     Domain,    ///< **domain** is a non-empty ASCII string that identifies a realm within a network
@@ -37,10 +40,10 @@ enum class HostType {
 };
 
 
-class host_output {
+class UPA_SO_VISIBLE host_output {
 protected:
     host_output() = default;
-    host_output(bool need_save)
+    inline host_output(bool need_save)
         : need_save_{ need_save } {}
 public:
     host_output(const host_output&) = delete;
@@ -49,7 +52,7 @@ class host_output {
 
     virtual std::string& hostStart() = 0;
     virtual void hostDone(HostType /*ht*/) = 0;
-    bool need_save() const noexcept { return need_save_; }
+    inline bool need_save() const noexcept { return need_save_; }
 private:
     bool need_save_ = true;
 };
@@ -74,7 +77,7 @@ class host_parser {
 // https://github.com/whatwg/url/pull/288
 // https://whatpr.org/url/288.html#urlhost-class
 
-class url_host {
+UPA_EXPORT class url_host {
 public:
     url_host() = delete;
     url_host(const url_host&) = default;
@@ -88,7 +91,7 @@ class url_host {
     ///
     /// @param[in] str Host string to parse
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    explicit url_host(const StrT& str) {
+    inline explicit url_host(const StrT& str) {
         host_out out(*this);
 
         const auto inp = make_str_arg(str);
@@ -103,34 +106,34 @@ class url_host {
     /// Host type getter
     ///
     /// @return host type, the one of: Domain, IPv4, IPv6
-    [[nodiscard]] HostType type() const {
+    [[nodiscard]] inline HostType type() const {
         return type_;
     }
 
     /// Hostname view
     ///
     /// @return serialized host as std::string_view
-    [[nodiscard]] std::string_view name() const UPA_LIFETIMEBOUND {
+    [[nodiscard]] inline std::string_view name() const UPA_LIFETIMEBOUND {
         return host_str_;
     }
 
     /// Hostname stringifier
     ///
     /// @return host serialized to string
-    [[nodiscard]] std::string to_string() const {
+    [[nodiscard]] inline std::string to_string() const {
         return host_str_;
     }
 
 private:
-    class host_out : public host_output {
+    class UPA_SO_VISIBLE host_out : public host_output {
     public:
-        explicit host_out(url_host& host)
+        inline explicit host_out(url_host& host)
             : host_(host)
         {}
-        std::string& hostStart() override {
+        inline std::string& hostStart() override {
             return host_.host_str_;
         }
-        void hostDone(HostType ht) override {
+        inline void hostDone(HostType ht) override {
             host_.type_ = ht;
         }
     private:
@@ -174,7 +177,7 @@ UPA_CONSTEXPR_20 bool contains_forbidden_host_char(const CharT* first, const Cha
 /// @param[in]  be_strict
 /// @param[in]  is_input_ascii
 /// @return `true` on success, or `false` on errors
-template <class CharT, class StrT, enable_if_str_arg_t<StrT> = 0>
+UPA_EXPORT template <class CharT, class StrT, enable_if_str_arg_t<StrT> = 0>
 inline bool domain_to_unicode(std::basic_string<CharT>& output, const StrT& input,
     bool be_strict = false, bool is_input_ascii = false)
 {
diff --git a/include/upa/url_ip.h b/include/upa/url_ip.h
index 7c8639d8..3ee42c03 100644
--- a/include/upa/url_ip.h
+++ b/include/upa/url_ip.h
@@ -9,12 +9,15 @@
 #include "config.h" // IWYU pragma: export
 #include "url_percent_encode.h"
 #include "url_result.h"
-#include <algorithm>
-#include <cstddef>
-#include <cstdint> // uint16_t, uint32_t, uint64_t
-#include <limits>
-#include <string>
-#include <type_traits>
+
+#ifndef UPA_MODULE
+# include <algorithm>
+# include <cstddef>
+# include <cstdint> // uint16_t, uint32_t, uint64_t
+# include <limits>
+# include <string>
+# include <type_traits>
+#endif // UPA_MODULE
 
 namespace upa {
 
diff --git a/include/upa/url_percent_encode.h b/include/upa/url_percent_encode.h
index 70e88153..f79b4bf2 100644
--- a/include/upa/url_percent_encode.h
+++ b/include/upa/url_percent_encode.h
@@ -14,16 +14,20 @@
 #include "str_arg.h"
 #include "url_utf.h"
 #include "util.h"
-#include <array>
-#include <cstdint> // uint8_t
-#include <initializer_list>
-#include <string>
-#include <type_traits>
-#include <utility>
+
+#ifndef UPA_MODULE
+# include <array>
+# include <cstdint> // uint8_t
+# include <initializer_list>
+# include <string>
+# include <type_traits>
+# include <utility>
+#endif // UPA_MODULE
 
 
 namespace upa {
 
+UPA_EXPORT_BEGIN
 
 /// @brief Represents code point set
 ///
@@ -163,6 +167,7 @@ inline constexpr code_point_set component_no_encode_set{ [](code_point_set& self
     self.exclude({ 0x24, 0x25, 0x26, 0x2B, 0x2C });
     } };
 
+UPA_EXPORT_END
 
 namespace detail {
 
@@ -506,6 +511,7 @@ inline void append_percent_decoded(StrT&& str, std::string& output) {
 
 } // namespace detail
 
+UPA_EXPORT_BEGIN
 
 /// @brief Percent decode input string.
 ///
@@ -558,6 +564,7 @@ template <class StrT, enable_if_str_arg_t<StrT> = 0>
     return percent_encode(std::forward<StrT>(str), component_no_encode_set);
 }
 
+UPA_EXPORT_END
 
 } // namespace upa
 
diff --git a/include/upa/url_result.h b/include/upa/url_result.h
index 4502b252..c14be0f8 100644
--- a/include/upa/url_result.h
+++ b/include/upa/url_result.h
@@ -1,4 +1,4 @@
-// Copyright 2016-2023 Rimas Misevičius
+// Copyright 2016-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
@@ -6,10 +6,16 @@
 #ifndef UPA_URL_RESULT_H
 #define UPA_URL_RESULT_H
 
-#include <stdexcept>
+#include "config.h"
+
+#ifndef UPA_MODULE
+# include <stdexcept>
+#endif // UPA_MODULE
 
 namespace upa {
 
+UPA_EXPORT_BEGIN
+
 /// @brief URL validation and other error codes
 ///
 /// See: https://url.spec.whatwg.org/#validation-error
@@ -94,26 +100,27 @@ enum class validation_errc {
 }
 
 /// @brief URL exception class
-
-class url_error : public std::runtime_error {
+class UPA_SO_VISIBLE url_error : public std::runtime_error {
 public:
     /// constructs a new url_error object with the given result code and error message
     ///
     /// @param[in] res validation error code
     /// @param[in] what_arg error message
-    explicit url_error(validation_errc res, const char* what_arg)
+    inline explicit url_error(validation_errc res, const char* what_arg)
         : std::runtime_error(what_arg)
         , res_(res)
     {}
 
     /// @return validation error code
-    [[nodiscard]] validation_errc result() const noexcept {
+    [[nodiscard]] inline validation_errc result() const noexcept {
         return res_;
     }
 private:
     validation_errc res_;
 };
 
+UPA_EXPORT_END
+
 namespace detail {
 
 /// @brief Result/value pair
diff --git a/include/upa/url_search_params-inl.h b/include/upa/url_search_params-inl.h
index 3a335729..0d96bbb5 100644
--- a/include/upa/url_search_params-inl.h
+++ b/include/upa/url_search_params-inl.h
@@ -1,4 +1,4 @@
-// Copyright 2016-2025 Rimas Misevičius
+// Copyright 2016-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
@@ -10,7 +10,9 @@
 #ifndef UPA_URL_SEARCH_PARAMS_INL_H
 #define UPA_URL_SEARCH_PARAMS_INL_H
 
-#include <memory> // std::addressof
+#ifndef UPA_MODULE
+# include <memory> // std::addressof
+#endif // UPA_MODULE
 
 
 namespace upa {
diff --git a/include/upa/url_search_params.h b/include/upa/url_search_params.h
index 5c666732..3e8fe2ce 100644
--- a/include/upa/url_search_params.h
+++ b/include/upa/url_search_params.h
@@ -10,14 +10,17 @@
 #include "str_arg.h"
 #include "url_percent_encode.h"
 #include "url_utf.h"
-#include <cassert>
-#include <list>
-#include <memory>
-#include <ostream>
-#include <string>
-#include <string_view>
-#include <type_traits>
-#include <utility>
+
+#ifndef UPA_MODULE
+# include <cassert>
+# include <list>
+# include <memory>
+# include <ostream>
+# include <string>
+# include <string_view>
+# include <type_traits>
+# include <utility>
+#endif // UPA_MODULE
 
 namespace upa {
 
@@ -45,19 +48,21 @@ constexpr bool is_iterable_pairs_v<T, std::void_t<decltype(
 // enable if `Base` is not the base class of `T`
 template<class Base, class T>
 using enable_if_not_base_of_t = std::enable_if_t<
-    !std::is_base_of_v<Base, std::decay_t<T>>, int
->;
+    !std::is_base_of_v<Base, std::decay_t<T>>, int>;
 
 } // namespace detail
 
 
 // forward declarations
 
-class url;
 namespace detail {
     class url_search_params_ptr;
 } // namespace detail
 
+UPA_EXPORT_BEGIN
+
+class url;
+
 /// @brief URLSearchParams class
 ///
 /// Follows specification in
@@ -103,7 +108,7 @@ class url_search_params
     ///
     /// @param[in] query string to parse
     template <class StrT, enable_if_str_arg_t<StrT> = 0>
-    explicit url_search_params(StrT&& query)
+    inline explicit url_search_params(StrT&& query)
         : params_(do_parse(true, std::forward<StrT>(query)))
     {}
 
@@ -115,7 +120,7 @@ class url_search_params
         detail::enable_if_not_base_of_t<url_search_params, ConT> = 0,
         std::enable_if_t<detail::is_iterable_pairs_v<ConT>, int> = 0
     >
-    explicit url_search_params(ConT&& cont) {
+    inline explicit url_search_params(ConT&& cont) {
         for (const auto& p : cont) {
             params_.emplace_back(make_string(p.first), make_string(p.second));
         }
@@ -303,38 +308,38 @@ class url_search_params
     // Iterators
 
     /// @return an iterator to the beginning of name-value list
-    [[nodiscard]] const_iterator begin() const noexcept { return params_.begin(); }
+    [[nodiscard]] inline const_iterator begin() const noexcept { return params_.begin(); }
 
     /// @return an iterator to the beginning of name-value list
-    [[nodiscard]] const_iterator cbegin() const noexcept { return params_.cbegin(); }
+    [[nodiscard]] inline const_iterator cbegin() const noexcept { return params_.cbegin(); }
 
     /// @return an iterator to the end of name-value list
-    [[nodiscard]] const_iterator end() const noexcept { return params_.end(); }
+    [[nodiscard]] inline const_iterator end() const noexcept { return params_.end(); }
 
     /// @return an iterator to the end of name-value list
-    [[nodiscard]] const_iterator cend() const noexcept { return params_.cend(); }
+    [[nodiscard]] inline const_iterator cend() const noexcept { return params_.cend(); }
 
     /// @return a reverse iterator to the beginning of name-value list
-    [[nodiscard]] const_reverse_iterator rbegin() const noexcept { return params_.rbegin(); }
+    [[nodiscard]] inline const_reverse_iterator rbegin() const noexcept { return params_.rbegin(); }
 
     /// @return a reverse iterator to the beginning of name-value list
-    [[nodiscard]] const_reverse_iterator crbegin() const noexcept { return params_.crbegin(); }
+    [[nodiscard]] inline const_reverse_iterator crbegin() const noexcept { return params_.crbegin(); }
 
     /// @return a reverse iterator to the end of name-value list
-    [[nodiscard]] const_reverse_iterator rend() const noexcept { return params_.rend(); }
+    [[nodiscard]] inline const_reverse_iterator rend() const noexcept { return params_.rend(); }
 
     /// @return a reverse iterator to the end of name-value list
-    [[nodiscard]] const_reverse_iterator crend() const noexcept { return params_.crend(); }
+    [[nodiscard]] inline const_reverse_iterator crend() const noexcept { return params_.crend(); }
 
     // Capacity
 
     /// Checks whether the name-value list is empty
     ///
     /// @return `true` if the container is empty, `false` otherwise
-    [[nodiscard]] bool empty() const noexcept { return params_.empty(); }
+    [[nodiscard]] inline bool empty() const noexcept { return params_.empty(); }
 
     /// @return the number of elements in the name-value list
-    [[nodiscard]] size_type size() const noexcept { return params_.size(); }
+    [[nodiscard]] inline size_type size() const noexcept { return params_.size(); }
 
     // Utils
 
@@ -376,6 +381,7 @@ class url_search_params
     url* url_ptr_ = nullptr;
 };
 
+UPA_EXPORT_END
 
 namespace detail {
 
@@ -395,20 +401,20 @@ class url_search_params_ptr
     // destructor
     UPA_CONSTEXPR_23 ~url_search_params_ptr() = default;
 
-    void init(url* url_ptr) {
+    inline void init(url* url_ptr) {
         ptr_.reset(new url_search_params(url_ptr)); // NOLINT(cppcoreguidelines-owning-memory)
     }
 
-    void set_url_ptr(url* url_ptr) noexcept {
+    inline void set_url_ptr(url* url_ptr) noexcept {
         if (ptr_)
             ptr_->url_ptr_ = url_ptr;
     }
 
-    void clear_params() noexcept {
+    inline void clear_params() noexcept {
         assert(ptr_);
         ptr_->clear_params();
     }
-    void parse_params(std::string_view query) {
+    inline void parse_params(std::string_view query) {
         assert(ptr_);
         ptr_->parse_params(query);
     }
@@ -750,6 +756,8 @@ inline std::string url_search_params::to_string() const {
     return query;
 }
 
+UPA_EXPORT_BEGIN
+
 // Non-member functions
 
 /// @brief Performs stream output on URL search parameters
@@ -777,6 +785,7 @@ inline void swap(url_search_params& lhs, url_search_params& rhs) noexcept {
     lhs.swap(rhs);
 }
 
+UPA_EXPORT_END
 
 } // namespace upa
 
diff --git a/include/upa/url_utf.h b/include/upa/url_utf.h
index 37a5bd21..a5e2fe4c 100644
--- a/include/upa/url_utf.h
+++ b/include/upa/url_utf.h
@@ -11,10 +11,12 @@
 
 #include "config.h" // IWYU pragma: export
 #include "url_result.h"
-#include <cstdint> // uint8_t, uint32_t
-#include <string>
-#include <string_view>
 
+#ifndef UPA_MODULE
+# include <cstdint> // uint8_t, uint32_t
+# include <string>
+# include <string_view>
+#endif // UPA_MODULE
 
 namespace upa {
 
@@ -49,7 +51,9 @@ class url_utf {
 private:
     // Replacement character (U+FFFD)
     static constexpr std::string_view kReplacementCharUtf8{ "\xEF\xBF\xBD" };
+};
 
+namespace detail {
     // Following two arrays have values from corresponding macros in ICU 74.1 library's
     // include\unicode\utf8.h file.
 
@@ -57,17 +61,23 @@ class url_utf {
     // Each bit indicates whether one lead byte + first trail byte pair starts a valid sequence.
     // Lead byte E0..EF bits 3..0 are used as byte index,
     // first trail byte bits 7..5 are used as bit index into that byte.
-    static constexpr std::uint8_t k_U8_LEAD3_T1_BITS[16] = {
+    inline constexpr std::uint8_t k_U8_LEAD3_T1_BITS[16] = {
         0x20, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x10, 0x30, 0x30
     };
     // Internal bit vector for 4-byte UTF-8 validity check, for use in U8_IS_VALID_LEAD4_AND_T1.
     // Each bit indicates whether one lead byte + first trail byte pair starts a valid sequence.
     // First trail byte bits 7..4 are used as byte index,
     // lead byte F0..F4 bits 2..0 are used as bit index into that byte.
-    static constexpr std::uint8_t k_U8_LEAD4_T1_BITS[16] = {
+    inline constexpr std::uint8_t k_U8_LEAD4_T1_BITS[16] = {
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1E, 0x0F, 0x0F, 0x0F, 0x00, 0x00, 0x00, 0x00
     };
-};
+
+    // For use with append_utf8 function. It appends a byte to output string.
+    template <typename CharT>
+    UPA_CONSTEXPR_20 void append_to_string(std::uint8_t c, std::basic_string<CharT>& str) {
+        str.push_back(static_cast<CharT>(c));
+    };
+} // namespace detail
 
 
 // The URL class (https://url.spec.whatwg.org/#url-class) in URL Standard uses
@@ -97,13 +107,6 @@ constexpr detail::result_value<std::uint32_t> url_utf::read_utf_char(const CharT
     return { false, 0xFFFD }; // REPLACEMENT CHARACTER
 }
 
-namespace detail {
-    template <typename CharT>
-    UPA_CONSTEXPR_20 void append_to_string(std::uint8_t c, std::basic_string<CharT>& str) {
-        str.push_back(static_cast<CharT>(c));
-    };
-} // namespace detail
-
 template <typename CharT>
 UPA_CONSTEXPR_20 void url_utf::read_char_append_utf8(const CharT*& it, const CharT* last, std::string& output) {
     const std::uint32_t code_point = read_utf_char(it, last).value;
@@ -140,11 +143,11 @@ constexpr bool url_utf::read_code_point(const char*& first, const char* last, st
             // fetch/validate/assemble all but last trail byte
             (c >= 0xE0 ?
                 (c < 0xF0 ? // U+0800..U+FFFF except surrogates
-                    k_U8_LEAD3_T1_BITS[c &= 0xF] & (1 << ((tmp = static_cast<std::uint8_t>(*first)) >> 5)) &&
+                    detail::k_U8_LEAD3_T1_BITS[c &= 0xF] & (1 << ((tmp = static_cast<std::uint8_t>(*first)) >> 5)) &&
                     (tmp &= 0x3F, 1)
                     : // U+10000..U+10FFFF
                     (c -= 0xF0) <= 4 &&
-                    k_U8_LEAD4_T1_BITS[(tmp = static_cast<std::uint8_t>(*first)) >> 4] & (1 << c) &&
+                    detail::k_U8_LEAD4_T1_BITS[(tmp = static_cast<std::uint8_t>(*first)) >> 4] & (1 << c) &&
                     (c = (c << 6) | (tmp & 0x3F), ++first != last) &&
                     (tmp = static_cast<std::uint8_t>(static_cast<std::uint8_t>(*first) - 0x80)) <= 0x3F) &&
                 // valid second-to-last trail byte
diff --git a/include/upa/urlpattern.h b/include/upa/urlpattern.h
index 1735371c..d480c63c 100644
--- a/include/upa/urlpattern.h
+++ b/include/upa/urlpattern.h
@@ -8,19 +8,21 @@
 #include "url.h" // NOLINT(llvm-include-order)
 #include "unicode_id.h"
 
-#include <algorithm>
-#include <cassert>
-#include <charconv>
-#include <cstdint>
-#include <optional>
-#include <stdexcept>
-#include <string>
-#include <string_view>
-#include <type_traits>
-#include <unordered_map>
-#include <utility>
-#include <variant>
-#include <vector>
+#ifndef UPA_MODULE
+# include <algorithm>
+# include <cassert>
+# include <charconv>
+# include <cstdint>
+# include <optional>
+# include <stdexcept>
+# include <string>
+# include <string_view>
+# include <type_traits>
+# include <unordered_map>
+# include <utility>
+# include <variant>
+# include <vector>
+#endif // UPA_MODULE
 
 namespace upa {
 namespace pattern {
@@ -132,6 +134,8 @@ struct has_regex_engine_members<T, std::void_t<
 
 } // namespace pattern
 
+UPA_EXPORT_BEGIN
+
 template<class T>
 constexpr bool is_regex_engine_v =
     std::is_default_constructible_v<T>
@@ -177,7 +181,7 @@ struct urlpattern_init {
     /// @brief Get value of member by name
     /// @param name Name of the member to get
     /// @return Value of the member if found, `std::nullopt` otherwise
-    [[nodiscard]] std::optional<std::string_view> get(std::string_view name) const {
+    [[nodiscard]] inline std::optional<std::string_view> get(std::string_view name) const {
         if (auto ptr = get_member(name))
             return this->*ptr;
         return std::nullopt;
@@ -187,7 +191,7 @@ struct urlpattern_init {
     /// @param name Name of the member to set
     /// @param value Value to set, must be assignable to std::string
     template <typename T, std::enable_if_t<std::is_assignable_v<std::string, T>, int> = 0>
-    void set(std::string_view name, T&& value) {
+    inline void set(std::string_view name, T&& value) {
         if (auto ptr = get_member(name))
             this->*ptr = std::forward<T>(value);
     }
@@ -198,6 +202,8 @@ struct urlpattern_init {
         get_member(std::string_view name);
 };
 
+UPA_EXPORT_END
+
 namespace pattern {
 
 // 1.6. Constructor string parsing
@@ -256,7 +262,6 @@ struct token {
     type type_;
     std::size_t index_;
     std::string_view value_;
-
 };
 
 // https://urlpattern.spec.whatwg.org/#token-list
@@ -447,6 +452,8 @@ constexpr bool hostname_pattern_is_ipv6_address(std::string_view input) noexcept
 
 } // namespace pattern
 
+UPA_EXPORT_BEGIN
+
 ///////////////////////////////////////////////////////////////////////
 // 1.2. The URLPattern class
 // https://urlpattern.spec.whatwg.org/#urlpattern-class
@@ -651,7 +658,7 @@ class urlpattern {
     /// @param[in] opt optional `upa::urlpattern_options` struct
     template <class T, class TB, upa::enable_if_str_arg_t<T> = 0,
         upa::enable_if_optional_str_arg_t<TB> = 0>
-    urlpattern(const T& input, TB&& base_url, urlpattern_options opt = {})
+    inline urlpattern(const T& input, TB&& base_url, urlpattern_options opt = {})
         : urlpattern{ make_urlpattern_init(input, std::forward<TB>(base_url)), opt } {}
 
     /// @brief Constructs urlpattern object from URL pattern string
@@ -667,7 +674,7 @@ class urlpattern {
     /// @param[in] input URL pattern string
     /// @param[in] opt optional `upa::urlpattern_options` struct
     template <class T, upa::enable_if_str_arg_t<T> = 0>
-    urlpattern(const T& input, urlpattern_options opt = {})
+    inline urlpattern(const T& input, urlpattern_options opt = {})
         : urlpattern{ make_urlpattern_init(input, std::nullopt), opt } {}
 
     /// @brief Test whether URL pattern matches the input
@@ -691,7 +698,7 @@ class urlpattern {
     ///   `false` otherwise
     template <class T, class TB = std::nullopt_t, upa::enable_if_str_arg_t<T> = 0,
         upa::enable_if_optional_str_arg_t<TB> = 0>
-    [[nodiscard]] bool test(const T& input, const TB& base_url_str = std::nullopt) const;
+    [[nodiscard]] bool test(const T& input, const TB& base_url_str = upa::nullopt) const;
 
     /// @brief Test whether URL pattern matches the URL.
     /// @param[in] url URL to test
@@ -754,7 +761,7 @@ class urlpattern {
         std::enable_if_t<std::is_base_of_v<urlpattern_result, ResT>, int> = 0,
         upa::enable_if_str_arg_t<T> = 0, upa::enable_if_optional_str_arg_t<TB> = 0>
     [[nodiscard]] std::optional<ResT> exec(const T& input,
-        const TB& base_url_str = std::nullopt) const;
+        const TB& base_url_str = upa::nullopt) const;
 
     /// @brief Executes the URL pattern against the URL
     ///
@@ -842,16 +849,18 @@ class urlpattern {
 /// @brief urlpattern exception class
 ///
 /// This exception can be thrown by the `upa::urlpattern` constructor in the case of an error.
-class urlpattern_error : public std::runtime_error {
+class UPA_SO_VISIBLE urlpattern_error : public std::runtime_error {
 public:
     /// constructs a new urlpattern_error object with the given error message
     ///
     /// @param[in] what_arg error message
-    explicit urlpattern_error(const char* what_arg)
+    inline explicit urlpattern_error(const char* what_arg)
         : std::runtime_error(what_arg)
     {}
 };
 
+UPA_EXPORT_END
+
 ///////////////////////////////////////////////////////////////////////
 // 1.2. The URLPattern class
 // https://urlpattern.spec.whatwg.org/#urlpattern-class
diff --git a/include/upa/util.h b/include/upa/util.h
index b049975a..3d5e15e6 100644
--- a/include/upa/util.h
+++ b/include/upa/util.h
@@ -7,17 +7,20 @@
 #define UPA_UTIL_H
 
 #include "config.h"
-#include <algorithm>
-#include <cassert>
-#include <cstddef>
-#include <limits>
-#ifdef __cpp_lib_start_lifetime_as
-# include <memory>
-#endif
-#include <stdexcept>
-#include <string>
-#include <string_view>
-#include <type_traits>
+
+#ifndef UPA_MODULE
+# include <algorithm>
+# include <cassert>
+# include <cstddef>
+# include <limits>
+# ifdef __cpp_lib_start_lifetime_as
+#  include <memory>
+# endif
+# include <stdexcept>
+# include <string>
+# include <string_view>
+# include <type_traits>
+#endif // UPA_MODULE
 
 namespace upa::util {
 
diff --git a/src/module/upa.url.cpp b/src/module/upa.url.cpp
new file mode 100644
index 00000000..bd7e8524
--- /dev/null
+++ b/src/module/upa.url.cpp
@@ -0,0 +1,29 @@
+// Copyright 2026 Rimas Misevičius
+// Distributed under the BSD-style license that can be
+// found in the LICENSE file.
+//
+module;
+
+#include "upa.url.h"
+
+// Macros
+#include "upa/config.h"
+#include "upa/url_version.h"
+
+#define UPA_IDNA_CPP_20
+#define UPA_IDNA_CONSTEXPR_20 constexpr
+
+module upa.url;
+
+#if (UPA_IMPORT_STD)
+import std;
+#endif
+
+#include "../idna.cpp"
+#include "../url.cpp"
+#include "../url_ip.cpp"
+#include "../url_search_params.cpp"
+#include "../url_utf.cpp"
+#include "../urlpattern.cpp"
+#include "../unicode_id.cpp"
+#include "../public_suffix_list.cpp"
diff --git a/src/module/upa.url.cppm b/src/module/upa.url.cppm
new file mode 100644
index 00000000..b6de712d
--- /dev/null
+++ b/src/module/upa.url.cppm
@@ -0,0 +1,18 @@
+// Copyright 2026 Rimas Misevičius
+// Distributed under the BSD-style license that can be
+// found in the LICENSE file.
+//
+module;
+
+#include "upa.url.h"
+
+export module upa.url;
+
+#if (UPA_IMPORT_STD)
+import std;
+#endif
+
+#include "upa/idna.h"
+#include "upa/url.h"
+#include "upa/urlpattern.h"
+#include "upa/public_suffix_list.h"
diff --git a/src/module/upa.url.h b/src/module/upa.url.h
new file mode 100644
index 00000000..81de02f7
--- /dev/null
+++ b/src/module/upa.url.h
@@ -0,0 +1,43 @@
+// Copyright 2026 Rimas Misevičius
+// Distributed under the BSD-style license that can be
+// found in the LICENSE file.
+//
+#define UPA_MODULE
+#define UPA_EXPORT export
+#define UPA_EXPORT_BEGIN export {
+#define UPA_EXPORT_END }
+
+#include <assert.h>
+#include <version>
+
+#ifndef UPA_IMPORT_STD
+# define UPA_IMPORT_STD 0
+#endif
+
+#if !(UPA_IMPORT_STD)
+# include <algorithm>
+# include <array>
+# include <charconv>
+# include <cstddef>
+# include <cstdint>
+# include <filesystem>
+# include <fstream>
+# include <functional>
+# include <initializer_list>
+# include <ios>
+# include <istream>
+# include <iterator>
+# include <limits>
+# include <list>
+# include <memory>
+# include <optional>
+# include <ostream>
+# include <stdexcept>
+# include <string>
+# include <string_view>
+# include <type_traits>
+# include <unordered_map>
+# include <utility>
+# include <variant>
+# include <vector>
+#endif
diff --git a/src/public_suffix_list.cpp b/src/public_suffix_list.cpp
index 433e9187..dc0743f0 100644
--- a/src/public_suffix_list.cpp
+++ b/src/public_suffix_list.cpp
@@ -1,11 +1,13 @@
-// Copyright 2024-2025 Rimas Misevičius
+// Copyright 2024-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
 // Formal algorithm:
 // https://github.com/publicsuffix/list/wiki/Format#formal-algorithm
 //
-#include "upa/public_suffix_list.h"
+#ifndef UPA_MODULE
+# include "upa/public_suffix_list.h"
+#endif // UPA_MODULE
 
 namespace upa {
 namespace {
diff --git a/src/unicode_id.cpp b/src/unicode_id.cpp
index 536d84a9..e36f3ed4 100644
--- a/src/unicode_id.cpp
+++ b/src/unicode_id.cpp
@@ -1,10 +1,12 @@
-// Copyright 2023-2025 Rimas Misevičius
+// Copyright 2023-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
-#include "upa/unicode_id.h"
-#include <cstddef>
-#include <cstdint>
+#ifndef UPA_MODULE
+# include "upa/unicode_id.h"
+# include <cstddef>
+# include <cstdint>
+#endif // UPA_MODULE
 
 namespace upa::pattern::table {
 namespace {
diff --git a/src/url.cpp b/src/url.cpp
index 143cfd04..87d74e06 100644
--- a/src/url.cpp
+++ b/src/url.cpp
@@ -2,8 +2,9 @@
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
-
-#include "upa/url.h"
+#ifndef UPA_MODULE
+# include "upa/url.h"
+#endif // UPA_MODULE
 
 namespace upa {
 namespace detail {
diff --git a/src/url_ip.cpp b/src/url_ip.cpp
index 37660c15..70cd1ca0 100644
--- a/src/url_ip.cpp
+++ b/src/url_ip.cpp
@@ -2,9 +2,10 @@
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
-
-#include "upa/url_ip.h"
-#include "upa/util.h"
+#ifndef UPA_MODULE
+# include "upa/url_ip.h"
+# include "upa/util.h"
+#endif // UPA_MODULE
 
 namespace upa {
 
diff --git a/src/url_search_params.cpp b/src/url_search_params.cpp
index b4f2a653..655040c6 100644
--- a/src/url_search_params.cpp
+++ b/src/url_search_params.cpp
@@ -2,10 +2,10 @@
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
-
-#include "upa/url_percent_encode.h"
-#include "upa/url_search_params.h"
-
+#ifndef UPA_MODULE
+# include "upa/url_percent_encode.h"
+# include "upa/url_search_params.h"
+#endif // UPA_MODULE
 
 namespace upa {
 namespace {
diff --git a/src/url_utf.cpp b/src/url_utf.cpp
index ff39160a..2c47e813 100644
--- a/src/url_utf.cpp
+++ b/src/url_utf.cpp
@@ -2,9 +2,10 @@
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
-
-#include "upa/url_utf.h"
-#include <cassert>
+#ifndef UPA_MODULE
+# include "upa/url_utf.h"
+# include <cassert>
+#endif // UPA_MODULE
 
 namespace upa {
 
diff --git a/src/urlpattern.cpp b/src/urlpattern.cpp
index 136a1e42..a16faf28 100644
--- a/src/urlpattern.cpp
+++ b/src/urlpattern.cpp
@@ -1,16 +1,17 @@
-// Copyright 2025 Rimas Misevičius
+// Copyright 2025-2026 Rimas Misevičius
 // Distributed under the BSD-style license that can be
 // found in the LICENSE file.
 //
-#include "upa/urlpattern.h"
-
-#include <array>
-#include <cassert>
-#include <cstdint>
-#include <optional>
-#include <string>
-#include <string_view>
-#include <utility>
+#ifndef UPA_MODULE
+# include "upa/urlpattern.h"
+# include <array>
+# include <cassert>
+# include <cstdint>
+# include <optional>
+# include <string>
+# include <string_view>
+# include <utility>
+#endif // UPA_MODULE
 
 namespace upa {
 namespace {
diff --git a/test/test-module.cpp b/test/test-module.cpp
new file mode 100644
index 00000000..50831066
--- /dev/null
+++ b/test/test-module.cpp
@@ -0,0 +1,142 @@
+// Copyright 2026 Rimas Misevičius
+// Distributed under the BSD-style license that can be
+// found in the LICENSE file.
+//
+#include "doctest-main.h"
+
+#include "upa/regex_engine_srell.h"
+
+#include <unordered_set>
+
+import upa.url;
+
+// Custom string class and it's specialization
+
+template <typename CharT>
+class CustomString {
+public:
+    CustomString(const CharT* data, std::size_t length)
+        : data_(data), length_(length) {}
+    const CharT* GetData() const { return data_; }
+    std::size_t GetLength() const { return length_; }
+private:
+    const CharT* data_ = nullptr;
+    std::size_t length_ = 0;
+};
+
+namespace upa {
+
+template<typename CharT>
+struct str_arg_char<CustomString<CharT>> {
+    using type = CharT;
+
+    static str_arg<CharT> to_str_arg(const CustomString<CharT>& str) {
+        return { str.GetData(), str.GetLength() };
+    }
+};
+
+} // namespace upa
+
+TEST_CASE("upa::url") {
+    upa::url url("https://user:psw@example.com:1234/p/a?q=Q#f");
+
+    CHECK(url.protocol() == "https:");
+    CHECK(url.username() == "user");
+    CHECK(url.password() == "psw");
+    CHECK(url.host() == "example.com:1234");
+    CHECK(url.hostname() == "example.com");
+    CHECK(url.port_int() == 1234);
+    CHECK(url.pathname() == "/p/a");
+    CHECK(url.search() == "?q=Q");
+    CHECK(url.hash() == "#f");
+
+    CHECK(url.pathname("../path"));
+    CHECK(url.pathname() == "/path");
+
+    upa::url url2{ url };
+    CHECK(url2.href() == url.href());
+
+    CHECK(upa::url::can_parse("about:blank"));
+
+    // Custom string
+    CHECK(upa::success(url.parse(CustomString<char>("about:blank", 11))));
+    CHECK(url.href() == "about:blank");
+}
+
+TEST_CASE("std::unordered_set<upa::url>") {
+    std::unordered_set<upa::url> aibe;
+    aibe.emplace(upa::url{ "about:blank" });
+    aibe.emplace(upa::url{ "file:///path" });
+    aibe.emplace(upa::url{ "https://example.org/" });
+
+    CHECK_FALSE(aibe.contains(upa::url{ "about:about" }));
+    CHECK(aibe.contains(upa::url{ "about:blank" }));
+}
+
+TEST_CASE("upa::url_search_params") {
+    constexpr auto get_eq =
+        [](upa::url_search_params& usp, const char* name, const char* value) {
+            return usp.get(name) && *usp.get(name) == value;
+        };
+
+    upa::url_search_params usp{ "a=2&c=1" };
+
+    CHECK(usp.size() == 2);
+    CHECK(get_eq(usp, "a", "2"));
+    CHECK(get_eq(usp, "c", "1"));
+    CHECK_FALSE(usp.has("b"));
+    usp.append("b", "3");
+    CHECK(usp.size() == 3);
+    CHECK(get_eq(usp, "b", "3"));
+    usp.set("a", "4");
+    CHECK(get_eq(usp, "a", "4"));
+    usp.remove("c");
+    CHECK_FALSE(usp.has("c"));
+}
+
+TEST_CASE("upa::url_host") {
+    upa::url_host host("www.example.com");
+    CHECK(host.to_string() == "www.example.com");
+    CHECK(host.type() == upa::HostType::Domain);
+
+    upa::url_host host2{ host };
+    CHECK(host2.to_string() == "www.example.com");
+}
+
+TEST_CASE("upa::public_suffix_list") {
+    upa::public_suffix_list psl;
+    upa::public_suffix_list::push_context ctx;
+    psl.push_line(ctx, "co.uk");
+    psl.finalize(ctx);
+
+    const auto registrable_domain = upa::public_suffix_list::option::registrable_domain;
+    CHECK(psl.get_suffix_view("www.example.co.uk", registrable_domain) == "example.co.uk");
+
+    upa::public_suffix_list psl2{ std::move(psl) };
+    CHECK(psl2.get_suffix_view("www.miestas.co.uk", registrable_domain) == "miestas.co.uk");
+
+    // Invalid hostname
+    CHECK(psl2.get_suffix_view("a^b.co.uk") == "");
+}
+
+TEST_CASE("upa::urlpattern") {
+    upa::urlpattern<upa::regex_engine_srell> urlp{ "https://*.example.com/*" };
+
+    CHECK(urlp.test("https://www.example.com/path"));
+    CHECK_FALSE(urlp.test("https://example.com/#1"));
+}
+
+TEST_CASE("upa::urlpattern_init") {
+    upa::urlpattern_init urlp_init;
+
+    urlp_init.protocol = upa::make_string(std::string("http:"));
+    urlp_init.hostname = upa::make_string("*.lt");
+    urlp_init.port = upa::make_string(L"80");
+    urlp_init.pathname = upa::make_string(u"/*");
+    urlp_init.set("search", upa::make_string(U"q=*"));
+    urlp_init.set("hash", "h");
+
+    upa::urlpattern<upa::regex_engine_srell> urlp{ urlp_init };
+    CHECK(urlp.test("http://www.example.lt/path?q=1#h"));
+    CHECK_FALSE(urlp.test("http://www.example.lt/path"));
+}