MCP + OpenAPI TypeScript stack (library-first)

This skill describes a reusable architecture pattern: a single package that can be an npm library, a CLI MCP process, and a thin MCP tool layer over a generated HTTP client. Reference implementations may use different file and function names; the roles stay the same.

Use it together with:

• mcp-builder — protocol framing, tool design, MCP SDK usage, evaluation.
• mcp-workflow-design — composite workflow tools on top of atomic 1:1 API tools.

Do not duplicate those skills here. This document answers: how is the code organized, why, and what to decide before adopting the pattern on a greenfield or existing MCP server.