When npm run dev does not bring up localhost:5173

Check what the script actually runs

The name dev is a convention, not a rule. It runs whatever package.json says it runs, and in a framework project that is often not vite directly.

$ npm run

# or read it straight out of the file
$ cat package.json

No script named dev

npm reports a missing script and lists the ones that exist. Some templates name it start, some serve. Run the one that is there.

npm error Missing script: "dev"

Available scripts are:
  build
  preview
  start

The script exists but vite is missing

The script runs and the shell cannot find the binary. npm looks in node_modules/.bin, so this means the dependency is not installed in this project — a fresh clone, an interrupted install, or an install that ran in a different directory. Installing again in the project root fixes it.

sh: vite: command not found

# Windows
'vite' is not recognized as an internal or external command

The config throws before the server starts

Vite loads vite.config.js before it binds to anything. A syntax error, a plugin that throws, or an import that does not resolve stops the start with a stack trace and no address block. Nothing is listening on 5173 in that state, so the browser error you get afterwards is a consequence, not the cause.

It started, but not on the port you are opening

Vite prints the address it actually bound to. If 5173 was taken it will have moved to 5174 and said so. A framework wrapper may set a different port entirely. Open the URL from the terminal, not the one you remember.

Port 5173 is in use, trying another one...

  ➜  Local:   http://localhost:5174/

It started and the terminal looks fine

Then the server is listening and the problem is on the way to it. Three candidates in order: you are on a different machine or container than the server (the address answers on localhost only), you typed https on a server serving http, or the app itself renders nothing. The first is a host problem, the last is not a dev-server problem at all.

The order that saves time

• Read the terminal to the end. Vite says what it bound to, or why it did not.
• No address block means it never started — the cause is above, in the same output.
• An address block with a different port means it started and you are opening the wrong URL.
• An address block and the right port means the server is fine; look at host, protocol, then your app.

• What happens between npm run dev and the page on localhost:5173Starting the Vite dev server takes five steps: npm resolves the vite binary, Vite reads the config, dependencies are pre-bundled, the server listens on 5173, and the browser opens an HMR WebSocket on the first request.
• Changing the port the Vite dev server usesSet server.port in vite.config.js, or pass --port on the command line; add strictPort: true if you want Vite to fail instead of silently moving to the next free port.
• Reaching the Vite dev server from anything other than localhostThe Vite dev server binds to localhost only and rejects unknown hostnames, so a second device, a container or a tunnel needs two separate settings: server.host to bind wider, and server.allowedHosts to accept the name being used.
• localhost:5173 — the port itselfWhat the address means, common dev ports, and the autocomplete fix.