Replit problems and how to fix them

Fixes for Replit apps that go offline, break on deploy or fail for visitors.

Replit app stops when I close the tab: how to keep it running
Your Replit app works while the editor is open, then the link dies. Why the replit.dev URL is temporary and how to publish a URL that stays up.
Replit works in dev but not in production: the real causes
Your Replit app works in the preview but the published site errors, shows no data or will not log in. Secrets, database and localhost causes, fixed.
Replit deployment failed health check: how to get it to publish
Replit publishing fails at the last step or the URL says the deployment could not be reached. Fix 0.0.0.0 binding, .replit ports and slow startup.
Replit app slow to load: cold starts and how to fix them
Your Replit app takes several seconds to show anything on the first visit. Why Autoscale cold starts happen and how to cut the wait or avoid it.
Replit custom domain not working: verifying, failed and SSL fixes
Your Replit custom domain is stuck on Verifying, shows Failed, or has SSL errors. Fix the A and TXT records, Cloudflare proxy, AAAA and CAA records.
Replit site not showing on Google: what to change
Your Replit site is missing from Google, or the replit.app address shows instead of your domain. Fix client-side meta tags, canonicals and sitemaps.