OpenAPI to Validated MCP Server
Build Python or TypeScript MCP servers from OpenAPI, with contract-derived schemas, safe API calls, and compatibility tests.
Before & after
Same prompt, same agent — the only difference is the skill.
Building an MCP server to expose your REST API is a good way to make it accessible to Claude. Here's the general approach: - Define the tools that map to your API endpoints - Implement handlers that call your API - Define input schemas for each tool - Handle authentication - Test the server with an MCP client You can build MCP servers in Python or TypeScript using the official SDKs. Each tool corresponds to an action Claude can take, with a schema describing its inputs. Hand-writing a wrapper for each endpoint works, but can be tedious for large APIs. How many endpoints does your API have?
Don't hand-write tool wrappers — generate the server from your OpenAPI
contract. That's the difference between a weekend of tedium that drifts
from the API, and a server that stays in sync with it.
FROM CONTRACT, NOT BY HAND
Point it at your OpenAPI spec → it generates the MCP tools:
each endpoint becomes a tool, with input schemas derived from the
spec's parameter definitions and validated against them. Python or
TypeScript.
Why this beats hand-writing:
• Schema validation is inherited from the contract — you don't
re-describe every parameter and risk describing it wrong.
• When the API changes, you regenerate. Hand-written wrappers drift
silently until a tool call fails in production.
• Large APIs are the same effort as small ones.
WHAT PRODUCTION-READY MEANS HERE
Not just "it calls the endpoint":
• Input validation at the tool boundary (from the schema), so a bad
call fails cleanly instead of hitting your API malformed.
• Auth handled once, not copy-pasted per tool.
• Safe evolution — the generated structure is designed to be
regenerated as the contract changes without hand-editing every tool.
THE SAFE-EVOLUTION POINT
This is the part hand-wrapping gets wrong. A hand-written MCP server is a
second source of truth that has to be manually kept in step with the
API. A contract-generated one has ONE source of truth — the OpenAPI spec
— so the API and the MCP server can't drift apart.
WHAT I NEED
Your OpenAPI spec (or the endpoint list + a note on auth). With the spec,
I scaffold the full server; without one, I can generate a spec from the
endpoints first, then build from that — which also leaves you with a
contract you didn't have.
Do you have an OpenAPI/Swagger spec, or just the running API?About this skill
Your API already has an OpenAPI contract, but turning every endpoint into a tool can produce confusing names, broken parameter handling, and dangerous write access. This skill turns selected operations into a Python or TypeScript MCP server, with schemas derived from the contract and explicit handling of authentication, errors, and API changes.
What it does
- Audits OpenAPI references, schema dialects, operation IDs, and security requirements before generating code.
- Selects useful operations and maps path, query, header, and body inputs without name collisions.
- Derives runtime validation using Zod or Pydantic, including separate request and response schemas.
- Implements contract-correct HTTP serialization, bounded requests, redacted errors, and controlled retries.
- Adds contract fixtures, MCP discovery and call checks, and compatibility checks for existing tools.
- Flags unsupported contract features and unresolved decisions instead of silently approximating them.
What you get
A reviewable server implementation or scaffold, an operation-to-tool map, focused tests, and setup instructions. The handoff distinguishes implemented behavior, executed checks, and remaining deployment requirements.
Best for
Engineers exposing an existing REST API to Claude or other MCP clients, especially teams maintaining OpenAPI contracts and evolving integrations without breaking existing tool consumers.
SKILL.md preview
---
name: openapi-to-validated-mcp-server
description: >-
Build Python or TypeScript MCP servers from selected OpenAPI operations, deriving runtime schemas, HTTP serialization, and compatibility tests from the contract. Use when the user says "turn this OpenAPI spec into MCP", "expose our REST API as tools", "scaffold a TypeScript MCP server", "generate Python tools from Swagger", "my MCP wrapper keeps rejecting valid inputs", "our API changed and broke the tools", or "review this generated MCP server".
---
# OpenAPI to Validated MCP Server
… (sign up to view the full skill)More development skills
View all Development skills →Performance Bottleneck Profiling: Node, Python, Go
Classifies a slowdown, gives exact profiler commands, reads the output, and proves the fix with same-conditions p95/p99 numbers.
Feature Scaffolding with Working Tests
Turn a short feature spec into code, runnable tests, and integration wiring that match your existing project.
Feature Flag Rollouts and Kill Switches
Design staged flag rollouts, verify rollback paths, and audit flag debt with explicit defaults, gates, and retirement plans.
Microcontroller Firmware and RTOS Engineering
Build and debug MCU firmware with bounded ISR/RTOS timing, safe DMA ownership, and measured power budgets.