Devs-Fix | Quick Solutions for Real-World Code Errors

You started your server and got Error: listen EADDRINUSE: address already in use :::3000 . It means exactly what it says: something already has port 3000 bound, and the operating system refused to hand it to your process. The :::3000 part is not a typo. Those three colons are an abbreviated IPv6 wildcard address ( :: ) followed by the port, so your server asked for every interface on port 3000 and lost. Ninety percent of the time the culprit is your own previous run that never fully exited. The rest of the time it is a second copy of your app, a Docker publish rule, a dev server with hot reload, a system service, or a bug in your own code that calls listen() twice. This page gives you the one-line fix first, then ten distinct causes with reproductions, then a checklist for the cases that do not match any of them. Error Error: listen EADDRINUSE: address already in use :::3000 Where it happens Node.js (any version) - Express, Fastify, Next.js, NestJS, Vite, webpack-dev-serve...