mcp-builder

name	mcp-builder
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).

MCP Server Development Guide

Create MCP servers enabling LLMs to accomplish real-world tasks through well-designed tools.

Stack

• Language: TypeScript (preferred) or Python
• Transport: Streamable HTTP (remote/stateless) · stdio (local)
• Validation: Zod (TS) or Pydantic (Python)

Workflow

Phase 1 — Research & Plan

1. Study the MCP spec: start at https://modelcontextprotocol.io/sitemap.xml, fetch pages with .md suffix
2. Load framework docs:
   • TS SDK: https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/main/README.md
   • Python SDK: https://raw.githubusercontent.com/modelcontextprotocol/python-sdk/main/README.md
3. Read ./reference/mcp_best_practices.md — naming, response format, pagination, security
4. Review target service API: endpoints, auth, data models

Phase 2 — Implement

1. Set up project — see ./reference/node_mcp_server.md (TS) or ./reference/python_mcp_server.md (Python)
2. Build shared utilities: API client + auth, error handling, response formatting, pagination
3. For each tool:
   • Input schema with Zod/Pydantic constraints and field descriptions
   • Output schema (outputSchema + structuredContent for TS SDK)
   • Concise description covering what it does, params, return type
   • Annotations: readOnlyHint, destructiveHint, idempotentHint, openWorldHint
   • Async/await, pagination support, actionable error messages

Phase 3 — Review & Test

1. Code quality: no duplication, consistent error handling, full types, clear descriptions
2. Build: npm run build (TS) or python -m py_compile (Python)
3. Test with MCP Inspector: npx @modelcontextprotocol/inspector

Phase 4 — Evaluations

Load ./reference/evaluation.md for full guidelines. Create 10 Q&A pairs:

• Tool inspection → content exploration (read-only) → generate questions → verify answers
• Each question: independent, read-only, complex (multi-tool), realistic, verifiable, stable

Output format:

<evaluation>
  <qa_pair><question>...</question><answer>...</answer></qa_pair>
</evaluation>

Key Design Principles

• Naming: consistent prefix + action-oriented (github_create_issue, github_list_repos)
• Coverage: prioritize comprehensive API coverage over workflow shortcuts
• Errors: always actionable — tell the agent what to do next
• Context: return focused, relevant data; support filtering and pagination

References

• ./reference/mcp_best_practices.md — universal guidelines (load first)
• ./reference/node_mcp_server.md — TypeScript patterns, examples, quality checklist
• ./reference/python_mcp_server.md — Python/FastMCP patterns, examples, quality checklist
• ./reference/evaluation.md — evaluation creation, XML format, running scripts