#48 most commondeployReplit

Replit deployment fails: app didn't open a port / health check failed

Your app is not responding on port ... / The deployment failed health checks / Your app must listen on 0.0.0.0

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What it means

When published, Replit waits for your app to answer on a specific port within a few seconds. Your app is either listening on the wrong address/port or taking too long to start.

How to fix it: paste this prompt into your AI builder

Fix prompt for Replit
My Replit deployment fails the port/health check. Make the server listen on host 0.0.0.0 and on process.env.PORT (with the fallback matching .replit), ensure .replit has exactly one [[ports]] entry mapping the app's localPort to externalPort 80, make the deployment run command start the production server (not the dev server or a one-off script), and make the home route respond quickly (move slow startup work after listen). Don't change app features.

If the AI can't fix it: manual steps

  1. Check the Deployment logs tab for the first error.
  2. Make sure the homepage route '/' returns something fast.

Where this happens

Seen in these AI app builders and editors:

Replit

Sources

Related deploy errors

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