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Replit errors and fixes

Errors running and deploying apps on Replit: ports, missing packages and apps that fail to respond after publishing.

4 Replit errors below. Each page shows the exact error text, what it means, likely causes and a step-by-step fix.

• Error: listen EADDRINUSE: address already in use
  Another process is already listening on the port your server is trying to use..
• Error: Cannot find module 'express'
  Node can't find a package (or local file) you required..
• ModuleNotFoundError: No module named 'flask'
  The Python interpreter running your code doesn't have the package installed..
• Application failed to respond
  Replit's proxy/health check could not reach your app process on the expected port.

Related error categories

• Node & Python runtime errors: 4 pages

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Other platforms

Next.js · Vercel · Supabase · Stripe · Cursor · Lovable · Bolt