FastAPI vs Node: when each one wins
Node wins on shared types with the frontend and ecosystem breadth. FastAPI wins on async correctness, schema-first APIs, and any service touching ML.
I run both in production. The question I get most: when do I pick one over the other? After enough projects, the heuristic is clear.
Node (with Nest or Fastify) is the right call when the service is tightly coupled to the frontend. Shared types, shared validation schemas, shared utilities — the monorepo benefits compound. The ecosystem is unmatched and the frontend team can ship backend changes without context-switching.
FastAPI wins when the service is data-heavy, ML-adjacent, or needs to be obviously correct under async load. Pydantic schemas double as OpenAPI specs, the type system catches a class of bugs Node's structural typing misses, and the Python ML ecosystem is right there. For a payment service, an inference API, or anything where correctness matters more than DX, I'll pick it every time.