Why Custom middleware creation in FastAPI? - Purpose & Use Cases

The Big Idea

What if you could add powerful features everywhere in your app with just one simple piece of code?

The Scenario

Imagine you want to log every request and response in your web app by adding code inside every route handler manually.

The Problem

Manually adding logging or checks in each route is repetitive, easy to forget, and clutters your code with extra details.

The Solution

Custom middleware lets you write one piece of code that runs before and after every request automatically, keeping your routes clean and consistent.

Before vs After

✗ Before

def route():
    log_request()
    process()
    log_response()

✓ After

class CustomMiddleware:
    async def __call__(self, request, call_next):
        log_request()
        response = await call_next(request)
        log_response()
        return response

What It Enables

You can add features like logging, authentication, or error handling globally without repeating code in every route.

Real Life Example

A company wants to track user activity on all pages to improve security and performance without changing each page's code.

Key Takeaways

Manual code repetition is slow and error-prone.

Middleware runs code automatically on every request.

Custom middleware keeps your app clean and consistent.