What Middleware Does and Why Backend Developers Rely on It

Middleware is code that executes between a server receiving a request and sending a response, sitting in a processing pipeline before the controller is reached. It can inspect, modify, forward, or block requests, handling cross-cutting concerns such as authentication, authorization, logging, input validation, and rate limiting. Without middleware, every controller would need to implement these checks independently, leading to repetitive and hard-to-maintain code. In frameworks like Express, middleware functions receive the request and response objects and call a next() function to pass control down the chain, or return an error response to halt processing. By centralizing reusable logic into dedicated middleware layers, backend developers keep controllers focused solely on business operations.