Middleware is software that sits between an incoming request and the code that finally answers it, handling the shared steps that nearly every request needs. Things like checking authentication, logging, parsing the request body and adding security headers live here, so the main code can stay focused on the actual job.
A good analogy is airport security. Before you reach your gate, every passenger passes through the same checkpoints: ticket scan, ID check, baggage screening. Nobody skips them, and the gate staff can assume anyone who arrives has already cleared all of it. Middleware is that row of checkpoints for a web request: each layer does one check and then waves the request on to the next. By the time the request reaches your back-end logic, the boring but necessary work is already done.
You see middleware most clearly in web frameworks. In Express.js, for example, you stack middleware functions in order, and each request flows through them one by one. A common chain handles authentication first, so unauthorized requests never reach the protected code at all. After that you might add rate limiting, then a JSON body parser, then your route handler.
Order is the part people get wrong. If you put the body parser after the route that needs the body, the data simply isn’t there yet. And a middleware that forgets to pass the request along will hang every call that reaches it. So the chain is powerful but unforgiving, and reading it top to bottom tells you exactly what happens to a request.
At TopDevs we use middleware to keep security and logging consistent across an entire application, so those rules are written once and applied everywhere instead of being copied into every endpoint.
