Generate from an OpenAPI spec

OpenAPI is mcpgen’s highest-fidelity input. Each operation becomes one MCP tool, with parameters, request bodies, auth, and (when present) response schemas carried straight into the IR.

Supported

OpenAPI 3.0 and 3.1, JSON or YAML.
Local file path or — in the web UI — pasted text or an http(s) URL the server fetches.
$refs are dereferenced (via @readme/openapi-parser) before parsing.

Generate


npx mcpgenx generate ./openapi.yaml --out ./my-server

Inspect first if you want to see the tool set:


npx mcpgenx inspect ./openapi.yaml

How operations map to tools

OpenAPI	IR / generated tool
`operationId`	sanitized into the MCP tool name (`[A-Za-z0-9_-]`, deduped)
`summary` / `description`	the tool description shown to the agent
path / query / header / cookie params	tool input fields with matching `location`
`requestBody`	`body` input field(s), Zod-validated
`responses` content schema	the tool’s `outputSchema` (used to mock the upstream during verify)
`security` + `securitySchemes`	the server’s auth wiring (see Adding auth)
`servers[].url`	default `MCPGEN_API_BASE_URL`

No operationId? mcpgen derives a stable name from the method and path (e.g. GET /pets/{petId} → getPetsPetId) and guarantees uniqueness.

Tips

Base URL — if the spec has no servers, set MCPGEN_API_BASE_URL in the generated .env before running.
Large specs — hundreds of operations generate fine; use inspect to sanity check the tool count first.
Response schemas help verification — specs that describe responses get better mocked-upstream smoke tests, since mcpgen can sample realistic results.