diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d54bc32..6c02a3d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -43,6 +43,7 @@ jobs:
               - 'capsule-core/**'
               - 'capsule-media/**'
               - 'capsule-sdk/**'
+              - 'xtask/**'
               - '.github/workflows/ci.yml'
             web:
               - 'capsule-web/**'
diff --git a/.markdownlint-cli2.jsonc b/.markdownlint-cli2.jsonc
index 26cec77..a48545e 100644
--- a/.markdownlint-cli2.jsonc
+++ b/.markdownlint-cli2.jsonc
@@ -22,6 +22,7 @@
         "**/dist/**",
         "**/.astro/**",
         "**/Derived/**",
-        "CLAUDE.md" // symlink to AGENTS.md
+        "CLAUDE.md", // symlink to AGENTS.md
+        "CHANGELOG.md" // generated by convco; not hand-formatted
     ]
 }
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..dacda02
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,8 @@
+# Changelog
+
+This file is generated from [Conventional Commits](https://www.conventionalcommits.org)
+by [convco](https://convco.github.io) — run `just changelog` (or let the release
+workflow do it). Section grouping is configured in `.versionrc`. Hand-edits made when
+cutting a release are reviewed in the release PR before the tag is pushed.
+
+## Unreleased
diff --git a/Cargo.lock b/Cargo.lock
index ef31257..3f60327 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4548,7 +4548,7 @@ version = "3.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e67ba7e9b2b56446f1d419b1d807906278ffa1a658a8a5d8a39dcb1f5a78614f"
 dependencies = [
- "toml_edit",
+ "toml_edit 0.25.12+spec-1.1.0",
 ]
 
 [[package]]
@@ -6998,6 +6998,12 @@ dependencies = [
  "winnow 0.7.15",
 ]
 
+[[package]]
+name = "toml_datetime"
+version = "0.6.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22cddaf88f4fbc13c51aebbf5f8eceb5c7c5a9da2ac40a13519eb5b0a0e8f11c"
+
 [[package]]
 name = "toml_datetime"
 version = "0.7.5+spec-1.1.0"
@@ -7016,6 +7022,18 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "toml_edit"
+version = "0.22.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41fe8c660ae4257887cf66394862d21dbca4a6ddd26f04a3560410406a2f819a"
+dependencies = [
+ "indexmap 2.14.0",
+ "toml_datetime 0.6.11",
+ "toml_write",
+ "winnow 0.7.15",
+]
+
 [[package]]
 name = "toml_edit"
 version = "0.25.12+spec-1.1.0"
@@ -7037,6 +7055,12 @@ dependencies = [
  "winnow 1.0.3",
 ]
 
+[[package]]
+name = "toml_write"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d99f8c9a7727884afe522e9bd5edbfc91a3312b36a77b5fb8926e4c31a41801"
+
 [[package]]
 name = "toml_writer"
 version = "1.1.1+spec-1.1.0"
@@ -8750,6 +8774,16 @@ version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "636f85e5ca6488e96401b61eb7de54f4e44755c988af0f52cf90230c312a1a89"
 
+[[package]]
+name = "xtask"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "regex",
+ "semver",
+ "toml_edit 0.22.27",
+]
+
 [[package]]
 name = "xxhash-rust"
 version = "0.8.15"
diff --git a/Cargo.toml b/Cargo.toml
index fe27c26..d051d0d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,6 +17,7 @@ members = [
     "capsule-core-ffi",
     "capsule-media",
     "capsule-sdk",
+    "xtask",
 ]
 # capsule-sdk requires a pre-generated openapi.json (run generate_openapi.sh first)
 default-members = [
diff --git a/capsule-android/build.gradle.kts b/capsule-android/build.gradle.kts
index 317169c..b527178 100644
--- a/capsule-android/build.gradle.kts
+++ b/capsule-android/build.gradle.kts
@@ -48,8 +48,10 @@ android {
         applicationId = "com.justin13888.capsule"
         minSdk = 26
         targetSdk = 36
-        versionCode = 1
-        versionName = "1.0"
+        // Version is the repo-wide source of truth in gradle.properties, kept in sync
+        // across every package by `just set-version` (xtask).
+        versionCode = providers.gradleProperty("capsule.versionCode").get().toInt()
+        versionName = providers.gradleProperty("capsule.versionName").get()
     }
     packaging {
         resources {
diff --git a/capsule-docs/package.json b/capsule-docs/package.json
index 437caae..d6d8073 100644
--- a/capsule-docs/package.json
+++ b/capsule-docs/package.json
@@ -1,7 +1,7 @@
 {
     "name": "capsule-docs",
     "type": "module",
-    "version": "0.0.1",
+    "version": "0.1.0",
     "scripts": {
         "dev": "astro dev",
         "start": "astro dev",
diff --git a/capsule-media/Cargo.toml b/capsule-media/Cargo.toml
index 650c69c..cb54fbf 100644
--- a/capsule-media/Cargo.toml
+++ b/capsule-media/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "capsule-media"
-version = "0.1.0"
+version.workspace = true
 edition = "2024"
 
 [dependencies]
diff --git a/capsule-swift/Project.swift b/capsule-swift/Project.swift
index 720025a..22e3297 100644
--- a/capsule-swift/Project.swift
+++ b/capsule-swift/Project.swift
@@ -6,10 +6,14 @@ private let bundlePrefix = "com.justin13888.capsule"
 private let appDestinations: Destinations = [.iPhone, .iPad]
 private let appDeploymentTargets: DeploymentTargets = .iOS("18.0")
 
-/// The Swift-6 language settings shared by every Capsule target.
+/// The Swift-6 language settings shared by every Capsule target. MARKETING_VERSION is
+/// the iOS app's version source of truth, kept in sync across every package by
+/// `just set-version` (xtask).
 private let baseSettings: SettingsDictionary = [
     "SWIFT_VERSION": "6.0",
     "SWIFT_STRICT_CONCURRENCY": "complete",
+    "MARKETING_VERSION": "0.1.0",
+    "CURRENT_PROJECT_VERSION": "1",
 ]
 
 /// Framework settings: a Release build marks the framework mergeable so the
diff --git a/gradle.properties b/gradle.properties
index 50c0048..cdda9ca 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -30,3 +30,9 @@ kotlin.incremental.js=true
 kotlin.incremental.multiplatform=true
 # Disable compiler cache for Linux (issue on Kotlin 2.1.20)
 kotlin.native.cacheKind.linuxX64=none
+
+# Capsule
+# Repo-wide version source of truth for the Android app. Kept in sync across every
+# package by `just set-version` (xtask), which also bumps versionCode on each release.
+capsule.versionName=0.1.0
+capsule.versionCode=1
diff --git a/justfile b/justfile
index 6ef15a1..9c08d9b 100644
--- a/justfile
+++ b/justfile
@@ -421,6 +421,18 @@ commit-check msg_file:
 check-commits base="origin/master":
     convco check --first-parent --ignore-reverts {{ base }}..HEAD
 
+# Write one repo-wide version into every package's source of truth (Rust workspace,
+# web/docs package.json, vision pyproject, Android gradle.properties, iOS Project.swift)
+# and bump the Android versionCode. See xtask/src/main.rs for the per-format editors.
+[group('release')]
+set-version version:
+    cargo run -q -p xtask -- set-version {{ version }}
+
+# Regenerate CHANGELOG.md from Conventional Commits. Hand-edits land in the release PR.
+[group('release')]
+changelog:
+    convco changelog > CHANGELOG.md
+
 # ── Setup ────────────────────────────────────────────────────────────────────
 
 [group('setup')]
diff --git a/xtask/Cargo.toml b/xtask/Cargo.toml
new file mode 100644
index 0000000..efce390
--- /dev/null
+++ b/xtask/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "xtask"
+version.workspace = true
+edition.workspace = true
+publish.workspace = true
+
+[dependencies]
+anyhow = "1"
+regex = "1"
+semver = "1"
+toml_edit = "0.22"
diff --git a/xtask/src/main.rs b/xtask/src/main.rs
new file mode 100644
index 0000000..6fc7aea
--- /dev/null
+++ b/xtask/src/main.rs
@@ -0,0 +1,228 @@
+//! Repo-maintenance tasks for the Capsule workspace.
+//!
+//! Currently one command, `set-version <X.Y.Z>`, which writes a single repo-wide
+//! version string into every package's source of truth so a release bump stays in
+//! sync across Rust, web, docs, Python, Android, and iOS. Each per-format editor is a
+//! pure `&str -> Result<String>` function so it can be unit-tested without disk I/O.
+
+use std::fs;
+use std::path::{Path, PathBuf};
+
+use anyhow::{Context, Result, bail};
+use regex::{Captures, Regex};
+use semver::Version;
+use toml_edit::Item;
+
+fn main() -> Result<()> {
+    let mut args = std::env::args().skip(1);
+    match args.next().as_deref() {
+        Some("set-version") => {
+            let raw = args.next().context("usage: xtask set-version <X.Y.Z>")?;
+            let version = Version::parse(&raw)
+                .with_context(|| format!("`{raw}` is not a valid semantic version"))?;
+            set_version(&repo_root(), &version.to_string())
+        }
+        Some(other) => bail!("unknown command `{other}`; usage: xtask set-version <X.Y.Z>"),
+        None => bail!("usage: xtask set-version <X.Y.Z>"),
+    }
+}
+
+/// The workspace root — `xtask` lives at `<root>/xtask`.
+fn repo_root() -> PathBuf {
+    Path::new(env!("CARGO_MANIFEST_DIR"))
+        .parent()
+        .map_or_else(|| PathBuf::from("."), Path::to_path_buf)
+}
+
+/// A per-format editor: rewrites file `contents` with the new `version`.
+type Editor = fn(&str, &str) -> Result<String>;
+
+/// Write `version` into every package's version source of truth.
+fn set_version(root: &Path, version: &str) -> Result<()> {
+    let edits: &[(&str, Editor)] = &[
+        ("Cargo.toml", set_cargo_workspace_version),
+        ("capsule-vision/pyproject.toml", set_pyproject_version),
+        ("capsule-web/package.json", set_package_json_version),
+        ("capsule-docs/package.json", set_package_json_version),
+        ("gradle.properties", set_gradle_properties_version),
+        ("capsule-swift/Project.swift", set_marketing_version),
+    ];
+    for (rel, edit) in edits {
+        let path = root.join(rel);
+        let input =
+            fs::read_to_string(&path).with_context(|| format!("reading {}", path.display()))?;
+        let output = edit(&input, version).with_context(|| format!("updating {rel}"))?;
+        if output == input {
+            println!("unchanged {rel}");
+        } else {
+            fs::write(&path, output).with_context(|| format!("writing {}", path.display()))?;
+            println!("updated   {rel} -> {version}");
+        }
+    }
+    Ok(())
+}
+
+/// Root `Cargo.toml`'s `[workspace.package] version` — the SSoT for every Rust crate.
+fn set_cargo_workspace_version(input: &str, version: &str) -> Result<String> {
+    let mut doc = input
+        .parse::<toml_edit::DocumentMut>()
+        .context("parsing Cargo.toml")?;
+    // toml_edit's chained `get_mut`/indexing auto-vivifies, so check existence first.
+    let exists = doc
+        .get("workspace")
+        .and_then(Item::as_table)
+        .and_then(|w| w.get("package"))
+        .and_then(Item::as_table)
+        .is_some_and(|p| p.contains_key("version"));
+    if !exists {
+        bail!("[workspace.package] version not found");
+    }
+    doc["workspace"]["package"]["version"] = toml_edit::value(version);
+    Ok(doc.to_string())
+}
+
+/// `capsule-vision/pyproject.toml`'s `[project] version`.
+fn set_pyproject_version(input: &str, version: &str) -> Result<String> {
+    let mut doc = input
+        .parse::<toml_edit::DocumentMut>()
+        .context("parsing pyproject.toml")?;
+    let exists = doc
+        .get("project")
+        .and_then(Item::as_table)
+        .is_some_and(|p| p.contains_key("version"));
+    if !exists {
+        bail!("[project] version not found");
+    }
+    doc["project"]["version"] = toml_edit::value(version);
+    Ok(doc.to_string())
+}
+
+/// The top-level `"version"` field of a `package.json` (formatting preserved).
+fn set_package_json_version(input: &str, version: &str) -> Result<String> {
+    replace_value(
+        input,
+        r#"(?m)^(?P<pre>\s*"version"\s*:\s*")[^"]*(?P<post>")"#,
+        version,
+        "\"version\" field",
+    )
+}
+
+/// Tuist's `MARKETING_VERSION` build setting in `Project.swift` — the iOS app version.
+fn set_marketing_version(input: &str, version: &str) -> Result<String> {
+    replace_value(
+        input,
+        r#"(?m)^(?P<pre>\s*"MARKETING_VERSION"\s*:\s*")[^"]*(?P<post>")"#,
+        version,
+        "MARKETING_VERSION setting",
+    )
+}
+
+/// `capsule.versionName` (set to `version`) and `capsule.versionCode` (incremented —
+/// it's a monotonic Android build number) in `gradle.properties`.
+fn set_gradle_properties_version(input: &str, version: &str) -> Result<String> {
+    let name_re = Regex::new(r"(?m)^capsule\.versionName=.*$").expect("static regex is valid");
+    if !name_re.is_match(input) {
+        bail!("capsule.versionName not found");
+    }
+    let with_name = name_re
+        .replace(input, |_: &Captures| {
+            format!("capsule.versionName={version}")
+        })
+        .into_owned();
+
+    let code_re = Regex::new(r"(?m)^capsule\.versionCode=(?P<code>\d+)[ \t]*$")
+        .expect("static regex is valid");
+    let next = code_re
+        .captures(&with_name)
+        .context("capsule.versionCode not found")?
+        .name("code")
+        .map(|m| m.as_str())
+        .unwrap_or_default()
+        .parse::<u64>()
+        .context("capsule.versionCode is not an integer")?
+        + 1;
+    Ok(code_re
+        .replace(&with_name, |_: &Captures| {
+            format!("capsule.versionCode={next}")
+        })
+        .into_owned())
+}
+
+/// Replace the value captured between named groups `pre` and `post` of the first match
+/// of `pattern` with `version`, erroring (via `what`) when nothing matches.
+fn replace_value(input: &str, pattern: &str, version: &str, what: &str) -> Result<String> {
+    let re = Regex::new(pattern).expect("static regex is valid");
+    if !re.is_match(input) {
+        bail!("{what} not found");
+    }
+    Ok(re
+        .replace(input, |caps: &Captures| {
+            format!("{}{version}{}", &caps["pre"], &caps["post"])
+        })
+        .into_owned())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn cargo_workspace_version_updates_and_preserves_rest() {
+        let input = "[workspace.package]\nversion = \"0.1.0\"\nedition = \"2024\"\n";
+        let out = set_cargo_workspace_version(input, "0.2.0").unwrap();
+        assert!(out.contains("version = \"0.2.0\""));
+        assert!(
+            out.contains("edition = \"2024\""),
+            "unrelated keys preserved"
+        );
+    }
+
+    #[test]
+    fn cargo_missing_version_errors() {
+        assert!(set_cargo_workspace_version("[workspace]\nmembers = []\n", "0.2.0").is_err());
+    }
+
+    #[test]
+    fn pyproject_version_updates() {
+        let input = "[project]\nname = \"capsule-vision\"\nversion = \"0.1.0\"\n";
+        let out = set_pyproject_version(input, "1.2.3").unwrap();
+        assert!(out.contains("version = \"1.2.3\""));
+        assert!(out.contains("name = \"capsule-vision\""));
+    }
+
+    #[test]
+    fn package_json_version_updates_field_and_keeps_formatting() {
+        let input =
+            "{\n  \"name\": \"capsule-web\",\n  \"version\": \"0.1.0\",\n  \"private\": true\n}\n";
+        let out = set_package_json_version(input, "0.2.0").unwrap();
+        assert!(out.contains("\"version\": \"0.2.0\""));
+        assert!(out.contains("\"name\": \"capsule-web\""));
+        assert!(out.contains("\"private\": true"));
+    }
+
+    #[test]
+    fn gradle_bumps_name_and_increments_code() {
+        let input = "capsule.versionName=0.1.0\ncapsule.versionCode=7\n";
+        let out = set_gradle_properties_version(input, "0.2.0").unwrap();
+        assert!(out.contains("capsule.versionName=0.2.0"));
+        assert!(
+            out.contains("capsule.versionCode=8"),
+            "versionCode is monotonic"
+        );
+    }
+
+    #[test]
+    fn marketing_version_updates() {
+        let input = "        \"MARKETING_VERSION\": \"0.1.0\",\n";
+        let out = set_marketing_version(input, "3.4.5").unwrap();
+        assert_eq!(out, "        \"MARKETING_VERSION\": \"3.4.5\",\n");
+    }
+
+    #[test]
+    fn missing_targets_error() {
+        assert!(set_gradle_properties_version("nope=1\n", "0.2.0").is_err());
+        assert!(set_marketing_version("no setting here\n", "0.2.0").is_err());
+        assert!(set_package_json_version("{}\n", "0.2.0").is_err());
+        assert!(set_pyproject_version("[tool]\nx = 1\n", "0.2.0").is_err());
+    }
+}