mcp-builder

mcp-builder

A Claude Code plugin that packages Anthropic's guide for building high-quality MCP (Model Context Protocol) servers, plus an evaluation harness for scoring them against QA-pair test suites.

What's in the plugin

• mcp-builder skill — Anthropic's 4-phase workflow (research → implement → test → evaluate) with per-language references for TypeScript (recommended) and Python. Activates automatically on prompts like "build an MCP server for X", "wrap the Y API as MCP tools", or "write an MCP server in TypeScript".
• /mcp-builder:evaluate slash command — Wraps scripts/evaluation.py. Takes a QA XML file plus a server description (stdio command, http URL, or sse URL) and returns a scored markdown report.

Install

From the Make Heavy Metal marketplace (recommended):

/plugin marketplace add make-heavy-metal/mcp-builder
/plugin install mcp-builder@make-heavy-metal

/plugin marketplace update make-heavy-metal pulls new versions when they ship.

For local development on the plugin itself: clone the repo and point Claude Code at it as a local marketplace:

git clone https://github.com/make-heavy-metal/mcp-builder.git
# then, inside Claude Code:
# /plugin marketplace add ./mcp-builder
# /plugin install mcp-builder@make-heavy-metal

Requirements

For the evaluation harness only:

pip install -r scripts/requirements.txt   # anthropic>=0.39.0, mcp>=1.1.0
export ANTHROPIC_API_KEY=...

The skill itself has no runtime dependencies — it's a guide the agent reads.

Usage

Build an MCP server — just describe what you want. The skill auto-activates:

"Build an MCP server in TypeScript that exposes the Linear API"

Evaluate a server — invoke the slash command with an eval file and a server description:

/mcp-builder:evaluate my-eval.xml stdio: node dist/index.js
/mcp-builder:evaluate my-eval.xml http://localhost:3000/mcp with header Authorization: Bearer $TOKEN

See scripts/example_evaluation.xml for the QA-pair format and skills/mcp-builder/references/evaluation.md for how to author good eval questions.

License

See LICENSE. Original content authored by Anthropic; packaged as a plugin by Travis Corrigan.