WorkerDockFree toolsFix “address already in use” for wrangler dev
Fix “address already in use” for wrangler dev
Pick the port from your error message and get the exact commands to find the process holding it, stop it, or run on a different port.
1. Find what is using the port
2. Stop it
3. Or run on a different port
Leftover workerd processes
Why this happens
wrangler dev listens on port 8787 by default, and also opens an inspector port, 9229 by default. If a previous run did not exit cleanly, for example because you closed the terminal tab, the old wrangler or workerd process can keep holding the port, and the next start fails with EADDRINUSE or "address already in use".
Common default ports
| Port | Used by |
|---|---|
| 8787 | wrangler dev (the Worker itself) |
| 9229 | The inspector used by wrangler dev |
| 4321 | astro dev |
| 5173 | Vite dev server, also used with the Cloudflare Vite plugin |
Change the port for good
Pass --port and --inspector-port on the command line, or set them in your Wrangler config under dev:
[dev] port = 8788 inspector_port = 9230
Frequently asked questions
Is it safe to kill the process?
Check the output of step 1 first. If it is node, wrangler or workerd from your own project, it is safe. If it is something you do not recognise, leave it alone and use a different port.
The port looks free but I still get the error.
Check the other port too. wrangler dev needs both the main port and the inspector port to be free.
Stop playing port roulette.
WorkerDock picks a free port for every project, shows what is running where, and stops a project's whole process group, including workerd, when you click Stop.