Web Framework

Libraries like Express, Django, Spring or FastAPI for building web apps.

Backend Engineer · Junior · core Frontend Engineer · Junior

Also known as: backend framework, web framework, Django, Flask, FastAPI, Express, Spring Boot, Rails, Laravel

A web framework is a library that handles the repetitive parts of building a web application, so you write the parts specific to your product.

# FastAPI
from fastapi import FastAPI
app = FastAPI()

@app.get("/hello/{name}")
def hello(name: str):
    return {"message": f"Hello, {name}"}

// Express
import express from "express";
const app = express();
app.get("/hello/:name", (req, res) => res.json({ message: `Hello, ${req.params.name}` }));
app.listen(3000);

Both do the same work: listen for requests, route them, read parameters, return JSON.

What frameworks typically provide

Routing from URLs to handlers.
Parsing of requests: headers, query strings, JSON bodies, forms.
Building responses with status codes and headers.
Middleware for shared concerns such as logging, authentication and CORS (middleware).
Often: templating, ORM, migrations, sessions, validation, an admin interface, testing tools.

Spectrum

Style	Examples	Trade-off
Minimal (“micro”)	Flask, Express, Sinatra	Flexible: you choose the other pieces
Batteries-included	Django, Rails, Laravel, Spring Boot	Fast to start and consistent, more conventions to learn

Frameworks exist for most languages (Python, JavaScript/TypeScript, Java, Ruby, PHP, Go, C#…).

Notes

A framework doesn’t serve traffic by itself. It runs inside a web server or application server (often via an interface such as WSGI/ASGI in Python).
Learn how requests flow through it (request lifecycle) because most debugging is about that.
Pick based on your language, team and ecosystem, and prefer mature, maintained, well-documented ones. Don’t rewrite in a new framework just because it’s fashionable.
Learn the underlying ideas (HTTP, routing, validation, persistence), and a second framework becomes easy.