yellhorn mcp

A Model Context Protocol (MCP) server that exposes Gemini 2.5 Pro capabilities to Claude Code for software development tasks.

Features

• Generate workplans: Creates GitHub issues with detailed implementation plans based on your codebase, with customizable title and detailed description
• Isolated Development Environments: Creates Git worktrees and linked branches for streamlined, isolated development workflow (can be done separately from workplan generation)
• Review Code Diffs: Evaluates pull requests against the original workplan with full codebase context and provides detailed feedback
• Seamless GitHub Integration: Automatically creates labeled issues with proper branch linking in the GitHub UI, posts reviews as PR comments with references to original issues, and handles asynchronous processing
• Context Control: Use .yellhornignore files to exclude specific files and directories from the AI context, similar to .gitignore
• MCP Resources: Exposes workplans as standard MCP resources for easy listing and retrieval

Installation

# Install from PyPI
pip install yellhorn-mcp

# Install from source
git clone https://github.com/msnidal/yellhorn-mcp.git
cd yellhorn-mcp
pip install -e .

Configuration

The server requires the following environment variables:

• GEMINI_API_KEY: Your Gemini API key (required)
• REPO_PATH: Path to your repository (defaults to current directory)
• YELLHORN_MCP_MODEL: Gemini model to use (defaults to "gemini-2.5-pro-exp-03-25")

The server also requires the GitHub CLI (gh) to be installed and authenticated.

Usage

Running the server

# As a standalone server
yellhorn-mcp --repo-path /path/to/repo --host 127.0.0.1 --port 8000

# Using the MCP CLI
mcp dev yellhorn_mcp.server

# Install as a permanent MCP server for Claude Desktop
mcp install yellhorn_mcp.server

# Set environment variables during installation
mcp install yellhorn_mcp.server -v GEMINI_API_KEY=your_key_here -v REPO_PATH=/path/to/repo

Integration with Claude Code

When working with Claude Code, you can use the Yellhorn MCP tools by:

1. Starting a project task:

Please generate a workplan with title "[Your Title]" and detailed description "[Your detailed requirements]"

1. Create a worktree for the workplan (optional):

Please create a worktree for issue #123

1. Navigate to the created worktree directory:

cd [worktree_path]  # The path is returned in the response

1. View the workplan if needed:

# Option 1: From the worktree directory (auto-detects issue number)
# While in the worktree directory
Please get the current workplan for this worktree

# Option 2: From the main repository (requires explicit issue number)
# You do not need to be in the worktree directory
Please get the workplan for issue #123

1. Make your changes, create a PR, and request a review:

# First create a PR using your preferred method (Git CLI, GitHub CLI, or web UI)
git add .
git commit -m "Implement feature"
git push origin HEAD
gh pr create --title "[PR Title]" --body "[PR Description]"

# Option 1: From the worktree directory (auto-detects issue number)
# While in the worktree directory, ask Claude to review it
Please trigger a review for PR "[PR URL]" against the original workplan

# Option 2: From the main repository (requires explicit issue number)
# You do not need to be in the worktree directory
Please trigger a review for PR "[PR URL]" against the workplan in issue #123

Tools

generate_workplan

Creates a GitHub issue with a detailed workplan based on the title and detailed description.

Input:

• title: Title for the GitHub issue (will be used as issue title and header)
• detailed_description: Detailed description for the workplan

Output:

• JSON string containing:
• issue_url: URL to the created GitHub issue
• issue_number: The GitHub issue number

create_worktree

Creates a git worktree with a linked branch for isolated development from an existing workplan issue.

Input:

• issue_number: The GitHub issue number for the workplan

Output:

• JSON string containing:
• worktree_path: Path to the created Git worktree directory
• branch_name: Name of the branch created for the worktree
• issue_url: URL to the associated GitHub issue

get_workplan

Retrieves the workplan content (GitHub issue body) associated with a workplan. Can be run from a worktree (auto-detects issue) or the main repo (requires explicit issue_number).

Input:

• issue_number: Optional issue number for the workplan. Required if run outside a Yellhorn worktree.

Output:

• The content of the workplan issue as a string

review_workplan

Triggers an asynchronous code review for a Pull Request against its original workplan issue. Can be run from a worktree (auto-detects issue) or the main repo (requires explicit issue_number).

Input:

• pr_url: The URL of the GitHub Pull Request to review
• issue_number: Optional issue number for the workplan. Required if run outside a Yellhorn worktree.

Output:

• A confirmation message that the review task has been initiated

Resource Access

Yellhorn MCP also implements the standard MCP resource API to provide access to workplans:

• list-resources: Lists all workplans (GitHub issues with the yellhorn-mcp label)
• get-resource: Retrieves the content of a specific workplan by issue number

These can be accessed via the standard MCP CLI commands:

# List all workplans
mcp list-resources yellhorn-mcp

# Get a specific workplan by issue number
mcp get-resource yellhorn-mcp 123

Development

# Install development dependencies
pip install -e ".[dev]"

# Run tests
pytest

CI/CD

The project uses GitHub Actions for continuous integration and deployment:

• Testing: Runs automatically on pull requests and pushes to the main branch
• Linting with flake8
• Format checking with black

• Testing with pytest

• Publishing: Automatically publishes to PyPI when a version tag is pushed

• Tag must match the version in pyproject.toml (e.g., v0.2.2)
• Requires a PyPI API token stored as a GitHub repository secret (PYPI_API_TOKEN)

To release a new version:

1. Update version in pyproject.toml
2. Commit changes: git commit -am "Bump version to X.Y.Z"
3. Tag the commit: git tag vX.Y.Z
4. Push changes and tag: git push && git push --tags

For more detailed instructions, see the Usage Guide.

License

MIT