HTTP Status Codes Cheat Sheet

2xx — Success

200 OK

High priority

The request succeeded and the page loaded correctly. This is the baseline you always want to see.

Monitor Assert 200 on every critical page — homepage, checkout, login. If it changes, something broke.

3xx — Redirects

301 Moved Permanently

Medium priority

The page has moved to a new URL permanently. Browsers and search engines update their records.

Monitor Alert on unexpected 301s — a misconfigured redirect can silently break pages and hurt SEO.

302 Found (Temporary Redirect)

Medium priority

The page temporarily lives elsewhere. Browsers follow it, but search engines keep the original URL.

Monitor A 302 where you expect 200 often means your CDN or auth layer is redirecting users unexpectedly.

4xx — Client Errors

401 Unauthorized

Medium priority

Access requires authentication. The server doesn't know who you are yet.

Monitor A public page returning 401 means broken auth — users are being blocked from content they should reach freely.

403 Forbidden

Medium priority

The server knows who you are but won't let you in. Access is explicitly denied.

Monitor Watch for 403 on public pages — usually caused by misconfigured server rules or permission errors after a deploy.

404 Not Found

High priority

The page doesn't exist at this URL. Could be deleted, moved, or mistyped.

Monitor Alert on 404 for key URLs. Also check for soft 404s — pages that return 200 but display a "not found" message.

429 Too Many Requests

Medium priority

The client has sent too many requests in too little time. The server is rate limiting.

Monitor A spike in 429s signals a traffic surge or a runaway API integration hammering your endpoints.

5xx — Server Errors

500 Internal Server Error

High priority

Something broke on the server. A catch-all for unhandled errors — the server doesn't know what else to say.

Monitor Alert immediately. Often triggered by bad deploys or database failures. Check your logs right away.

502 Bad Gateway

High priority

A gateway or proxy received an invalid response from an upstream server.

Monitor Common during and after deployments. Brief but impactful — users get errors that won't show in logs without monitoring.

503 Service Unavailable

High priority

The server is temporarily unable to handle the request — overloaded or down for maintenance.

Monitor Expected during planned downtime — configure a monitoring window to suppress alerts. Any other 503 needs immediate attention.

504 Gateway Timeout

High priority

The gateway didn't get a response from the upstream server in time. Something upstream is too slow.

Monitor Correlate with response time data. Often a sign of database slowdown under load — the issue starts before the timeout hits.

HTTP Status CodesCheat Sheet

HTTP Status Codes
Cheat Sheet