Instant reference for HTTP 2xx, 3xx, 4xx, and 5xx response codes. Understand root causes, debugging checklists, and remediation commands.
The standard response for successful HTTP requests.
The request succeeded and a new resource was created.
The target resource has been permanently assigned a new URI.
The server cannot process the request due to malformed syntax.
Authentication is required and has failed or has not yet been provided.
The server understands the request but refuses to authorize it.
The requested resource could not be found on the server.
The user has sent too many requests in a given amount of time (rate limited).
The server encountered an unexpected condition preventing it from fulfilling the request.
The proxy/load balancer received an invalid response from the upstream server.
The server is currently unable to handle the request due to temporary overload or maintenance.
The proxy/load balancer did not receive a timely response from the upstream server.
The server encountered an unexpected condition preventing it from fulfilling the request.
Unhandled exception in backend code, database connection drop, or unhandled null pointer.
Inspect application error logs and APM stack traces to resolve uncaught exceptions.
curl https://api.yourdomain.com/v1/crash
Everything you need to know about API uptime, SLA calculations, and monitoring with Uptara.
4xx status codes (e.g. 400, 401, 404, 429) indicate client-side errors such as invalid request formatting, missing authentication, or rate limiting. 5xx status codes (e.g. 500, 502, 503, 504) indicate server-side failures such as uncaught exceptions, upstream proxy failures, or backend timeouts.
Automate status code validation and receive alerts on 5xx/4xx spikes.
Calculate allowed outage duration for 99.9% and 99.99% availability targets.
Detect latency spikes before they escalate into 504 Gateway Timeouts.