Claude mcp-builder skill

MCP (Model Context Protocol) is how Claude connects to outside services: an MCP server wraps an API as tools Claude can call. Anthropic's mcp-builder skill is a development guide for writing those servers in Python with FastMCP or in TypeScript with the MCP SDK. It is one of Anthropic's open-source example skills, under the Apache 2.0 license. If you are unsure whether you need a skill or an MCP server, our Claude Skills manual compares the two.

What the skill does

The SKILL.md runs in four phases:

1. Research and planning. Claude reads the MCP specification and the SDK documentation, studies the target API's endpoints and authentication, and lists the tools to build, starting with the most common operations.
2. Implementation. Shared code for the API client, errors, pagination and response formatting, then each tool with an input schema (Zod or Pydantic), a clear description and annotations that mark it read-only, destructive or idempotent.
3. Review and test. A build or syntax check, then a run in MCP Inspector (npx @modelcontextprotocol/inspector).
4. Evaluations. Ten realistic, read-only questions with verifiable answers, saved as XML, to test whether a model can actually use the server.

Its defaults: TypeScript as the recommended language, streamable HTTP for remote servers and stdio for local ones. It also stresses tool names with a consistent prefix, such as github_create_issue, and error messages that tell the agent what to try next.

When to use it

• Connecting Claude to an internal API or a SaaS tool that has no MCP server yet.
• Reviewing an existing server against a checklist before you share it.
• Writing evaluation questions for a server you already have.

Keep the Claude Code cheat sheet nearby while you build, and see our Claude Code prompts for planning and review requests. Our Claude Code overview covers plans and setup.

How to install it

Claude Code, where most server work happens:

/plugin marketplace add anthropics/skills
/plugin install example-skills@anthropic-agent-skills

Claude.ai: the anthropics/skills README says its example skills are already available on paid plans.

Example request

Use the mcp-builder skill to build an MCP server for [service] in [TypeScript / Python]. Its API docs are at [URL]. Start with read-only tools for [the 3-5 things you need], authenticate with [method], and write the ten evaluation questions at the end.

Limits

• Phase one fetches the MCP and SDK documentation from the web, so it needs network access. On the Claude API, skills run without network access.
• The server holds whatever credentials you give it. Review the code, start with read-only tools and keep keys out of the repository.
• Anthropic labels its example skills as demonstrations and advises testing before you rely on them.

FAQ

Should I build a skill or an MCP server?

A skill describes how to do a task. An MCP server gives Claude access to a service. Build a server when Claude needs to read or change data in another system.