Bun.js middleware in 2026: what it is, how it works, how to optimize it, and where not to break your API (opens in new tab)

A practical guide to middleware in Bun.js: native Bun.serve, Hono, Elysia, auth, CORS, rate limiting, logging, observability, performance, best practices, and bad practices. We explain when middleware helps, when it creates latency, and how to build production-ready APIs on Bun.