micro

micro is a minimal Node.js library from Vercel for writing single-purpose HTTP services as plain async functions. A microservice is just a module that exports (req, res) => {} (or returns a value directly), and micro handles response serialization, error status codes, and body-parsing helpers like json, text, and buffer around the standard Node http request/response objects.

The project intentionally stays under a megabyte with all dependencies and has no built-in middleware system by design — services are expected to compose plain functions rather than depend on a plugin ecosystem. It ships both as a programmatic API (serve, send, createError) and a micro CLI for running a service in production.

What You Get

• A serve(fn) wrapper that turns an async (req, res) => value function into a standard Node HTTP handler
• Body-parsing helpers buffer, text, and json with configurable size limits
• A send(res, statusCode, data) helper that serializes objects, buffers, and streams with correct headers
• Structured error handling via createError and automatic statusCode-aware error responses
• A micro CLI for running a service against TCP, UNIX socket, or Windows named pipe endpoints

Common Use Cases

• Writing a small, single-purpose HTTP endpoint deployed in its own container
• Building lightweight internal APIs without pulling in a full web framework’s routing and middleware stack
• Parsing JSON or urlencoded request bodies in a Node service with explicit size limits
• Prototyping an HTTP service quickly with plain async functions instead of framework boilerplate

Under The Hood

Architecture - The published micro package lives in a small pnpm/lerna monorepo (packages/micro) with the library implementation under packages/micro/src/lib (the serve, send, buffer/text/json, and error-handling functions) and a separate CLI entry point under packages/micro/src/bin that resolves a service’s main file and starts an HTTP server listening on TCP, UNIX socket, or named-pipe endpoints. Tech Stack - Written in TypeScript, compiled with tsc to a dist folder with generated .d.ts types, and designed to have effectively no runtime dependencies of its own beyond Node’s built-in http module, keeping the installed package under a megabyte. Code Quality - The project ships a dedicated errors workspace package alongside micro and a test directory exercising body-parsing and error-handling behavior; the codebase has stayed small (~260 lines was the historical target) across 436 commits and 61 tagged releases, prioritizing stability over feature growth. API Design - The public API is deliberately tiny — one wrapper function (serve), three body helpers, and one response helper — with no middleware system, so services are just plain async functions; this keeps the learning curve minimal but pushes cross-cutting concerns like auth or logging onto explicit function composition rather than a plugin ecosystem.