Adding OpenAPI Support to Mummy, a Nim HTTP Framework

Nim doesn't have a lot of options for building HTTP APIs with the kind of batteries-included developer experience you get in frameworks like FastAPI or Express with Swagger middleware. mummy is a fast, solid HTTP/WebSocket server library for Nim (my fork with the additions below is at github.com/isaiahpeter/mummy ) — but out of the box, it doesn't generate OpenAPI specs, validate request bodies, or give you typed path parameters. So I forked it and added those. This post walks through what I built, why, and what I learned extending an existing Nim library instead of starting from scratch. Why mummy, and why OpenAPI I wanted a Nim backend for a few projects (a contact-form API, a todo API demo) and kept missing three things I'd take for granted in other ecosystems: Auto-generated API docs — a /docs endpoint you can actually hand to someone, generated from your routes instead of hand-written. Typed path parameters — pulling id out of /users/{id} as an int without manual parsing and error handling in every handler. Request validation — rejecting a bad JSON body before it reaches your handler logic, with a schema to back it up. mummy is fast and minimal by design, which is exactly why it was worth extending rather than replacing. What I added OpenAPI spec generation. I added openapi_schema.nim and openapi_router.nim , which let you wrap routes in an OpenApiRouter and attach a summary, tags, and a response schema via schemaOf . The router serves both /openapi.json and a browsable /docs page generated from your actual route definitions — so the docs can't drift out of sync with the code the way hand-written API docs do. Typed path parameters. pathParam[T](request, "id") pulls a path segment and parses it as the type you ask for, with a clean 400 response if parsing fails. One gotcha worth flagging if you try this yourself: in this Nim version, the generic dot-call form ( request.pathParam[int]("id") ) doesn't parse — you have to call it as pathParam[int](request, "id") in