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HTTP errors

Status codes from servers and APIs—404, 500, redirects, and what they usually mean.

• 400 Bad RequestThe server cannot process the request—malformed syntax, bad JSON, or invalid parameters.
• 401 UnauthorizedAuthentication failed or was missing—bad credentials, expired token, or wrong auth scheme.
• 403 ForbiddenThe server refuses to fulfill the request—permissions, IP rules, or policy blocked access.
• 404 Not FoundThe server has no resource for the URL you requested—often routing, a bad link, or a missing file.
• 408 Request TimeoutThe server gave up waiting for the full request—slow uploads or idle connections.
• 429 Too Many RequestsThe client sent too many requests in a window—rate limits, quotas, or abuse protection.
• 500 Internal Server ErrorThe server hit an unexpected failure while handling the request—check application and dependency logs.
• 502 Bad GatewayA proxy or edge server received an invalid or empty response from an upstream server.
• 503 Service UnavailableThe server is temporarily unable to serve traffic—overload, maintenance, or dependency outage.
• 504 Gateway TimeoutA proxy waited too long for an upstream response—slow database, cold starts, or network latency.
• Cloudflare 522 — connection timed outCloudflare could not connect to your origin in time—origin down, firewall, or slow TLS.
• Cloudflare 525 — SSL handshake failedCloudflare could not complete TLS with your origin—cert mismatch, wrong port, or TLS version.
• Heroku H10 — app crashedThe web process exited; Heroku serves an error page. Logs show the real exception.
• Kubernetes CrashLoopBackOffThe container exits repeatedly—check logs, probes, and resource limits.
• Netlify — page not foundThe deploy exists but no asset matches the path—often SPA routing or a missing file in publish dir.
• Vercel — deployment not foundThe deployment URL or project alias does not exist or was removed.