HTTP Status Codes

HTTP status codes are three-digit numbers returned by a web server to indicate the result of a request. They are essential for debugging web applications, configuring APIs, building integrations, and understanding what happens when a browser or client makes a request. The first digit tells you the general category: 1xx (informational), 2xx (success), 3xx (redirection), 4xx (client error), or 5xx (server error).

401 means the client is not authenticated — they have not provided valid credentials (or none at all). The server sends a WWW-Authenticate header asking for them. 403 means the client is authenticated but does not have permission to access the resource. With 401, try logging in or providing credentials; with 403, the credentials are valid but lack the necessary permissions.

301 Moved Permanently means the resource has a new URL and all future requests should go there. Search engines update their index to the new URL. 302 Found (Temporary Redirect) means the resource is temporarily at a different URL but clients should keep using the original URL for future requests. 307 and 308 are the modern equivalents that preserve the HTTP method (POST stays POST).

502 Bad Gateway means a server acting as a gateway or proxy received an invalid response from an upstream server. For example, a load balancer forwards a request to a backend server, but the backend crashes or returns something malformed. It is usually a server-side issue that requires checking the upstream server health, logs, and network connectivity.

500 Internal Server Error is a generic catch-all for unexpected server conditions — a crash, an uncaught exception, or a misconfiguration. 503 Service Unavailable means the server is temporarily overloaded or down for maintenance and expects to recover. A 503 often includes a Retry-After header suggesting when to retry, while 500 usually requires checking server logs to diagnose.

429 Too Many Requests means the client has exceeded the server's rate limit. The server is throttling the client to prevent abuse or overload. The response should include a Retry-After header indicating how many seconds to wait before retrying. This is common in public API usage — implement exponential backoff and respect the Retry-After header.

304 Not Modified is sent when a client sends conditional headers like If-Modified-Since or If-None-Match, and the server determines the resource has not changed since the last request. The response has no body — the browser uses its cached copy. This reduces bandwidth and speeds up page loads for returning visitors. It is a key part of HTTP caching strategy.

Yes — completely free, no registration, and 100% private. The entire database of status codes is built into the page and runs locally in your browser. Nothing is uploaded, stored, or logged. The tool works offline after the page loads.