express

Express is a minimal and flexible web framework for Node.js — the JavaScript runtime that lets you run JavaScript on a server rather than just in a browser. It is one of the most widely used web frameworks in the JavaScript ecosystem, providing the essential building blocks for creating web servers and HTTP APIs without imposing a rigid structure on how you organize your application.

What it does is give you a straightforward way to handle HTTP requests and send back responses. You define routes — essentially rules that say "when someone visits this URL with this method (GET, POST, etc.), run this function." Express takes care of parsing the incoming request, matching it to the right route, and giving you simple tools to send back text, HTML, JSON, or whatever the client needs. It also supports middleware, which are small functions that run before your route handlers, used for tasks like logging, authentication, or parsing request bodies.

The framework is intentionally kept small and unopinionated, meaning it does not dictate which database you use, which template engine renders your HTML, or how you structure your files. This makes it highly composable — you add exactly the pieces you need, and nothing more. It supports over 14 template engines for server-side HTML rendering and includes built-in helpers for things like redirects and caching.

You would reach for Express whenever you need to build a web server, a REST API, or a backend for a web or mobile application using JavaScript. It is especially popular for single-page application backends, internal APIs, and small-to-medium web services. The project runs on Node.js 18 or higher and is installed via npm.