MCP Builder - Claude Skill for Building MCP Servers

Source: Content adapted from anthropics/skills (MIT). Last synced July 8, 2026, against the April 20, 2026 upstream update.

Overview

The official description: "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)."

This is the skill to reach for when you want Claude to scaffold an MCP server that other agents can actually rely on - it bakes in research, implementation patterns, and an evaluation loop.

How the skill works

The SKILL.md organizes the build into three phases:

1. Phase 1 - Deep research and planning: understand modern MCP design, study the protocol docs and the target framework (FastMCP for Python, MCP SDK for Node/TypeScript), then plan the tool surface before writing code.
2. Phase 2 - Implementation: set up the project structure, implement core infrastructure, then implement tools one by one with well-designed inputs, outputs, and error messages.
3. Phase 3 - Review and test: code-quality pass, then build and test - including agent-facing evaluations, not just unit tests.

What's inside the skill folder

• reference/mcp_best_practices.md - the design rules tools must follow
• reference/python_mcp_server.md and reference/node_mcp_server.md - per-stack implementation references
• reference/evaluation.md plus scripts/evaluation.py, scripts/example_evaluation.xml - a working evaluation harness
• scripts/connections.py, scripts/requirements.txt

Key takeaways for your own skills

• The skill treats evaluation as part of the deliverable: an MCP server ships with an eval suite, not just endpoints.
• Splitting per-language references into separate files keeps the main SKILL.md small enough to load fast - a pattern worth copying in any multi-stack skill.

See it on GitHub

skills/mcp-builder