Replit deployment fails or published app won't load (server must listen on 0.0.0.0)

What it means in plain English

Replit's published app must accept outside connections. A server listening only on localhost is invisible to the internet.

Likely causes

• Server listens on localhost/127.0.0.1 instead of 0.0.0.0.
• Ports in .replit set without externalPort = 80.
• Secrets not set for the deployment.
• Slow startup failing the health check.

How to fix it, step by step

1. In your server code, listen on host 0.0.0.0 (e.g. app.listen(port, '0.0.0.0')).
2. If .replit defines ports, include one with externalPort = 80.
3. Add your Secrets to the deployment (production secrets).
4. Check the deployment logs for the real error.
5. Make sure the run/build commands match what works in Preview.

How to check it worked

• Publishing completes and the public URL loads the main flow.

Sources

• https://docs.replit.com/cloud-services/deployments/troubleshooting (opens in a new tab)