Claude skill · Development · Anthropic

MCP server builder skill for Claude

A four-phase guide to building good MCP servers in Python (FastMCP) or TypeScript, from research and tool design to testing and evaluations.

Command: /mcp-builder
Licence: Apache-2.0, copying allowed with attribution
Folder: 10 files, 119 KB
Runs code: 2 scripts

Overview

What it does

The workflow runs from research and planning (study the API, then balance full endpoint coverage with task-focused workflow tools, favouring coverage when unsure) through implementation and review to writing evaluations: realistic questions that check an agent can actually use the server.

Reference files cover MCP best practices and separate Python and Node guides, loaded only in the phase that needs them. A bundled script runs the evaluations against your server.

Triggers

When Claude uses it

Building an MCP server to connect an external API or service to an LLM.

Its description, which Claude matches against

Guide for creating high-quality MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools. Use when building MCP servers to integrate external APIs or services, whether in Python (FastMCP) or Node/TypeScript (MCP SDK).

What it needs

Python or Node.js. The evaluation script needs the anthropic and mcp Python packages and an Anthropic API key, so running it uses paid API credit.

Install

How to install it

Claude Code

Plugin (type in Claude Code)

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

The example-skills plugin installs 12 skills from this repository, including this one. Its skills are then namespaced, such as /example-skills:mcp-builder.

Or copy the folder (shell)

git clone --depth 1 https://github.com/anthropics/skills.git
mkdir -p ~/.claude/skills
cp -r skills/skills/mcp-builder ~/.claude/skills/

That makes it a personal skill, available as /mcp-builder in all your projects. Copy it into .claude/skills/ in a repository instead to share it with your team.

claude.ai and the Claude API

Zip the skill folder, then in claude.ai open Customize > Skills, choose + and Create skill, then Upload a skill. Code execution must be turned on.

Upload with the Python SDK

from anthropic import Anthropic
from anthropic.lib import files_from_dir

client = Anthropic()
skill = client.skills.create(files=files_from_dir("mcp-builder"))
print(skill.id)  # use as a custom skill_id with the code execution tool

Checks

SKILL.md validator results

Its SKILL.md (236 lines) run through our SKILL.md validator, with the folder’s file list, for both targets. These check the file’s format, not whether the skill works well.

Claude Code

0 errors, 0 warnings, 1 tip

tipSKILL.md doesn’t mention scripts/connections.py, scripts/example_evaluation.xml. Say what each file is for and when to read or run it, or Claude won’t know to use it.

claude.ai and the API

0 errors, 0 warnings, 2 tips

tipThe Claude Help Center’s upload guide gives a 200-character description limit for claude.ai, though the platform docs say 1,024. Keep it under 200 if you’ll upload it there.
tipSKILL.md doesn’t mention scripts/connections.py, scripts/example_evaluation.xml. Say what each file is for and when to read or run it, or Claude won’t know to use it.

Folder

What’s in the folder

LICENSE.txt11 KB
SKILL.md8.9 KB
reference/4 files, 81 KB
scripts/4 files, 18 KB

SKILL.md sections

MCP Server Development Guide
Overview
Process
🚀 High-Level Workflow
Phase 1: Deep Research and Planning
Phase 2: Implementation
Phase 3: Review and Test
Phase 4: Create Evaluations
Reference Files
📚 Documentation Library
Core MCP Documentation (Load First)
SDK Documentation (Load During Phase 1/2)
Language-Specific Implementation Guides (Load During Phase 2)
Evaluation Guide (Load During Phase 4)

Source

Licence and source

Published by Anthropic in anthropics/skills/skills/mcp-builder, last changed 2026-04-20.
Licence: Apache-2.0, copying allowed with attribution. Our copy of the SKILL.md is unmodified, served with its licence.
Read from commit dbd4588; write-up checked 2026-10-14.
Before installing, read the SKILL.md on GitHub and its scripts. Anthropic advises using skills only from sources you trust (security considerations).

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What it does

When Claude uses it

What it needs

How to install it

Claude Code

claude.ai and the Claude API

SKILL.md validator results

Claude Code

claude.ai and the API

What’s in the folder

SKILL.md sections

Licence and source

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