--- title: "mcp-builder skill: build and test an MCP server for any API" canonical_url: https://cookiesforai.app/skills/anthropics/mcp-builder last_updated: 2026-10-02T01:58:30+02:00 type: skill summary: "MCP Builder is Anthropic's open-source agent skill for building MCP servers in TypeScript or Python, from API research and tool design to testing and a 10-question evaluation." install: "/plugin marketplace add anthropics/skills" related: - "https://cookiesforai.app/skills/obra/writing-skills" - "https://cookiesforai.app/skills/anthropics/skill-creator" - "https://cookiesforai.app/skills/anthropics/academy-guide" - "https://cookiesforai.app/skills/anthropics/algorithmic-art" - "https://cookiesforai.app/skills/anthropics/brand-guidelines" - "https://cookiesforai.app/skills/anthropics/canvas-design" --- # MCP Builder MCP Builder is Anthropic's open-source agent skill for building MCP servers in TypeScript or Python, from API research and tool design to testing and a 10-question evaluation. | Fact | Value | |---|---| | Publisher | Anthropic (official, own GitHub account) | | Source | https://github.com/anthropics/skills/tree/HEAD/skills/mcp-builder | | License | Apache-2.0 | | Repository stars | 179,326 on 2026-10-02 | | Skill name | mcp-builder | | Category | Building skills and MCP servers | | Skill last changed | 2026-04-20 | | Page updated | 2026-10-02 | | Facts checked | 2026-10-02 | ## Install In Claude Code, add Anthropic's skills marketplace: ``` /plugin marketplace add anthropics/skills ``` Then install the example-skills plugin, which holds this skill and Anthropic's other example skills: ``` /plugin install example-skills@anthropic-agent-skills ``` Or install only this skill, for any agent, with the skills CLI: ``` npx skills add anthropics/skills --skill mcp-builder ``` In Claude.ai, Anthropic says its example skills are already available on paid plans: switch them on under Customize > Skills. ## Ask your coding agent A skill can include scripts that run on your computer, so read its source first: https://github.com/anthropics/skills/tree/HEAD/skills/mcp-builder ```text Install the agent skill mcp-builder from github.com/anthropics/skills. ``` ## What it does MCP Builder is Anthropic's guide to building MCP (Model Context Protocol) servers, which let AI models use an external API or service through tools. It loads when you build an MCP server in Python with FastMCP or in TypeScript with the official MCP SDK. It recommends TypeScript, with streamable HTTP for remote servers and stdio for local ones. With MCP Builder, the agent works in four phases. It studies the MCP specification and the service's API, then plans which endpoints to cover, starting with the most common operations. It implements tools with Zod or Pydantic input schemas, consistent name prefixes, pagination, actionable error messages and hints such as read-only or destructive. Then it builds the server and tests it with the MCP Inspector. Reference files cover best practices and each language. The last MCP Builder phase is an evaluation: 10 realistic, read-only questions, each with one verifiable answer, saved as an XML file. A bundled Python script runs those questions against your server through Claude, over stdio, SSE or HTTP, and reports the results along with Claude's feedback on the tools. It needs the anthropic and mcp Python packages and an ANTHROPIC_API_KEY. ## When to use it - You want Claude or another agent to use your product's API and need an MCP server for it. - You are designing MCP tools and want naming, pagination and error handling conventions to follow. - You built an MCP server and want to test whether a model can answer real questions with it. ## When to pick something else - You want to package know-how or a workflow rather than tools: write a skill with Skill Creator or Writing Skills. ## Which agents it works in Anthropic documents it for Claude Code, Claude.ai, Claude API. The open skills CLI also installs it into 78 agents (listed with the CLI on 2026-10-01). Building the server works in any agent, but the evaluation script calls Claude through the Anthropic API, so that step needs an ANTHROPIC_API_KEY whichever agent you use. ## License Apache-2.0. Apache-2.0 comes from the LICENSE.txt in the skill's own folder (read 2026-10-01); the anthropics/skills repository has no root license file. In practice you may use, change and share the skill in any agent, commercially too, as long as you keep the license text and notices and mark your changes. ## Questions people ask ### Do I need an Anthropic API key for mcp-builder? Only for the evaluation: its Python script runs your 10 questions through Claude and needs the anthropic and mcp packages plus an ANTHROPIC_API_KEY. Researching, designing and building the server works without one. ### Should I build my MCP server in Python or TypeScript? The skill supports both, FastMCP for Python and the official MCP SDK for TypeScript, and recommends TypeScript, with streamable HTTP for remote servers and stdio for local ones. ## Related ### Related skills for building skills and mcp servers - [Writing Skills](https://cookiesforai.app/skills/obra/writing-skills): Writing Skills is an agent skill from Superpowers: your agent writes new skills test-first, running pressure scenarios with subagents before and after the skill exists. - [Skill Creator](https://cookiesforai.app/skills/anthropics/skill-creator): Skill Creator is Anthropic's open-source agent skill for making skills: the agent drafts a SKILL.md with you, tests it with and without the skill, and tunes its description so it triggers. ### More from Anthropic - [Academy Guide](https://cookiesforai.app/skills/anthropics/academy-guide): Academy Guide is Anthropic's agent skill that ends Claude's answers about using Claude with one or two matching Claude Academy courses or tutorials, and only when the match is strong. - [Algorithmic Art](https://cookiesforai.app/skills/anthropics/algorithmic-art): Algorithmic Art is Anthropic's open-source agent skill for generative art: the agent writes a short art philosophy, then builds an interactive p5.js piece with seeds and parameter sliders. - [Brand Guidelines](https://cookiesforai.app/skills/anthropics/brand-guidelines): Brand Guidelines is Anthropic's open-source agent skill that holds Anthropic's own brand colors and fonts, so an agent can give a document, slide deck or web artifact the Anthropic look. - [Canvas Design](https://cookiesforai.app/skills/anthropics/canvas-design): Canvas Design is Anthropic's open-source agent skill for static visual work: the agent writes a design philosophy, then makes a poster or art piece as a finished PNG or PDF file.