diff --git a/lib/locallingo/providers/ruby_llm.rb b/lib/locallingo/providers/ruby_llm.rb
index cf02751..3be1077 100644
--- a/lib/locallingo/providers/ruby_llm.rb
+++ b/lib/locallingo/providers/ruby_llm.rb
@@ -54,6 +54,7 @@ def ensure_credentials!
       # the model and return the parsed JSON object as a Hash.
       def chat(model:, instructions:, payload:)
         require "ruby_llm"
+        configure_credentials!
 
         conversation = ::RubyLLM.chat(
           model:,
@@ -64,6 +65,26 @@ def chat(model:, instructions:, payload:)
         response = conversation.ask(JSON.pretty_generate(payload))
         JsonExtraction.extract_object(response.content)
       end
+
+      private
+
+      # RubyLLM does not read provider API keys from ENV on its own, so a
+      # standalone CLI run (no Rails initializer to call RubyLLM.configure)
+      # would raise "Missing configuration for <provider>". Fill the
+      # provider's key from ENV — unless the host app already configured
+      # one, which always wins.
+      def configure_credentials!
+        env = CREDENTIAL_ENV[provider]
+        return unless env
+
+        setting = "#{provider}_api_key"
+        config = ::RubyLLM.config
+        return unless config.respond_to?(setting) && config.respond_to?("#{setting}=")
+        return unless config.public_send(setting).to_s.strip.empty?
+
+        key = ENV.fetch(env, "")
+        config.public_send("#{setting}=", key) unless key.strip.empty?
+      end
     end
   end
 end
diff --git a/spec/locallingo/providers/ruby_llm_spec.rb b/spec/locallingo/providers/ruby_llm_spec.rb
new file mode 100644
index 0000000..171bb16
--- /dev/null
+++ b/spec/locallingo/providers/ruby_llm_spec.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+require "ruby_llm"
+
+RSpec.describe Locallingo::Providers::RubyLLM do
+  subject(:provider) { described_class.new(provider: :anthropic) }
+
+  describe "#chat" do
+    let(:conversation) { double }
+    let(:response) { double(content: '{"greeting":"hallo"}') }
+
+    before do
+      allow(RubyLLM).to receive(:chat).and_return(conversation)
+      allow(conversation).to receive_messages(with_instructions: conversation, ask: response)
+    end
+
+    around do |example|
+      original = RubyLLM.config.anthropic_api_key
+      example.run
+    ensure
+      RubyLLM.config.anthropic_api_key = original
+    end
+
+    it "configures the provider API key from ENV before chatting" do
+      RubyLLM.config.anthropic_api_key = nil
+      stub_const("ENV", ENV.to_h.merge("ANTHROPIC_API_KEY" => "env-key-123"))
+
+      result = provider.chat(model: "claude-x", instructions: "translate", payload: { "greeting" => "hello" })
+
+      expect(RubyLLM.config.anthropic_api_key).to eq("env-key-123")
+      expect(result).to eq({ "greeting" => "hallo" })
+    end
+
+    it "does not clobber a key the host app already configured" do
+      RubyLLM.config.anthropic_api_key = "explicit-app-key"
+      stub_const("ENV", ENV.to_h.merge("ANTHROPIC_API_KEY" => "env-key-123"))
+
+      provider.chat(model: "claude-x", instructions: "translate", payload: { "greeting" => "hello" })
+
+      expect(RubyLLM.config.anthropic_api_key).to eq("explicit-app-key")
+    end
+
+    it "leaves configuration untouched when the ENV var is absent" do
+      RubyLLM.config.anthropic_api_key = nil
+      stub_const("ENV", ENV.to_h.except("ANTHROPIC_API_KEY"))
+
+      provider.chat(model: "claude-x", instructions: "translate", payload: { "greeting" => "hello" })
+
+      expect(RubyLLM.config.anthropic_api_key).to be_nil
+    end
+  end
+end