Claude Code runs npm run dev and then just hangs

Solved · 391 views · asked 2 months ago by jonah_b · edited

Very often Claude says "Let me start the dev server to test" and runs npm run dev. Then it just sits there for minutes with the server output scrolling. I have to press Esc and then it's confused.

Also sometimes it starts a second one and I get Port 3000 is in use, trying 3001 instead.

What I’ve tried

Told it not to, but after a /clear it does it again.

Comment

Do you have anything about the dev server in CLAUDE.md? tom_brewer 2 months ago · edited

2 answers

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tom_brewer2 months ago · edited

The dev server never "finishes", so a normal command waits forever. Two fixes:

Put it in CLAUDE.md so it survives /clear:

## Dev server
- I run the dev server myself on port 3000. Never start it.
- To verify changes, run `npm run build` and `npm run lint`.

If you do want it to start one, it can run commands in the background (Ctrl+B while a command runs moves it there), then it can read the output later without blocking.

The Port 3000 is in use thing is a sign there are leftover servers; lsof -i :3000 shows them.

Comment

CLAUDE.md fix works, it now runs build instead. Didn't know about ctrl+b. jonah_b last month · edited

sanne_devlast month · edited

If you want it to check pages visually, a Playwright MCP against your already-running server works better than it starting its own.

Comment

Will look at that for layout checks, thanks. jonah_b last month · edited

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Claude Code runs npm run dev and then just hangs

What I’ve tried

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Claude Code runs npm run dev and then just hangs

What I’ve tried

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