claude-code-action/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Development Tools

• Runtime: Bun 1.2.11
• TypeScript with strict configuration

Common Development Tasks

Available npm/bun scripts from package.json:

# Test
bun test

# Formatting
bun run format          # Format code with prettier
bun run format:check    # Check code formatting

# Type checking
bun run typecheck       # Run TypeScript type checker

Architecture Overview

This is a GitHub Action that enables Claude to interact with GitHub PRs and issues. The action operates in two main phases:

Phase 1: Preparation (src/entrypoints/prepare.ts)

1. Authentication Setup: Establishes GitHub token via OIDC or GitHub App
2. Permission Validation: Verifies actor has write permissions
3. Trigger Detection: Uses mode-specific logic to determine if Claude should respond
4. Context Creation: Prepares GitHub context and initial tracking comment

Phase 2: Execution (base-action/)

The base-action/ directory contains the core Claude Code execution logic, which serves a dual purpose:

• Standalone Action: Published separately as @anthropic-ai/claude-code-base-action for direct use
• Inner Logic: Used internally by this GitHub Action after preparation phase completes

Execution steps:

1. MCP Server Setup: Installs and configures GitHub MCP server for tool access
2. Prompt Generation: Creates context-rich prompts from GitHub data
3. Claude Integration: Executes via multiple providers (Anthropic API, AWS Bedrock, Google Vertex AI)
4. Result Processing: Updates comments and creates branches/PRs as needed

Key Architectural Components

Mode System (src/modes/)

• Tag Mode (tag/): Responds to @claude mentions and issue assignments
• Agent Mode (agent/): Direct execution when explicit prompt is provided
• Extensible registry pattern in modes/registry.ts

GitHub Integration (src/github/)

• Context Parsing (context.ts): Unified GitHub event handling
• Data Fetching (data/fetcher.ts): Retrieves PR/issue data via GraphQL/REST
• Data Formatting (data/formatter.ts): Converts GitHub data to Claude-readable format
• Branch Operations (operations/branch.ts): Handles branch creation and cleanup
• Comment Management (operations/comments/): Creates and updates tracking comments

MCP Server Integration (src/mcp/)

• GitHub Actions Server (github-actions-server.ts): Workflow and CI access
• GitHub Comment Server (github-comment-server.ts): Comment operations
• GitHub File Operations (github-file-ops-server.ts): File system access
• Auto-installation and configuration in install-mcp-server.ts

Authentication & Security (src/github/)

• Token Management (token.ts): OIDC token exchange and GitHub App authentication
• Permission Validation (validation/permissions.ts): Write access verification
• Actor Validation (validation/actor.ts): Human vs bot detection

Project Structure

src/
├── entrypoints/           # Action entry points
│   ├── prepare.ts         # Main preparation logic
│   ├── update-comment-link.ts  # Post-execution comment updates
│   └── format-turns.ts    # Claude conversation formatting
├── github/               # GitHub integration layer
│   ├── api/              # REST/GraphQL clients
│   ├── data/             # Data fetching and formatting
│   ├── operations/       # Branch, comment, git operations
│   ├── validation/       # Permission and trigger validation
│   └── utils/            # Image downloading, sanitization
├── modes/                # Execution modes
│   ├── tag/              # @claude mention mode
│   ├── agent/            # Automation mode
│   └── registry.ts       # Mode selection logic
├── mcp/                  # MCP server implementations
├── prepare/              # Preparation orchestration
└── utils/                # Shared utilities

Important Implementation Notes

Authentication Flow

• Uses GitHub OIDC token exchange for secure authentication
• Supports custom GitHub Apps via APP_ID and APP_PRIVATE_KEY
• Falls back to official Claude GitHub App if no custom app provided

MCP Server Architecture

• Each MCP server has specific GitHub API access patterns
• Servers are auto-installed in ~/.claude/mcp/github-{type}-server/
• Configuration merged with user-provided MCP config via mcp_config input

Mode System Design

• Modes implement Mode interface with shouldTrigger() and prepare() methods
• Registry validates mode compatibility with GitHub event types
• Agent mode triggers when explicit prompt is provided

Comment Threading

• Single tracking comment updated throughout execution
• Progress indicated via dynamic checkboxes
• Links to job runs and created branches/PRs
• Sticky comment option for consolidated PR comments

Code Conventions

• Use Bun-specific TypeScript configuration with moduleResolution: "bundler"
• Strict TypeScript with noUnusedLocals and noUnusedParameters enabled
• Prefer explicit error handling with detailed error messages
• Use discriminated unions for GitHub context types
• Implement retry logic for GitHub API operations via utils/retry.ts