HTTP Status Codes: Complete Reference Guide | Free Tool

A The 401 Unauthorized status code means a request lacks valid authentication credentials. The server requires the client to log in. In contrast, 403 Forbidden means the server understands the request but refuses to authorize it, even with valid credentials, due to insufficient permissions. Our HTTP Status Code Reference tool helps you quickly compare these subtle differences, providing detailed descriptions and use cases to accurately diagnose access control and authentication issues.

A Absolutely. When you're working with APIs, understanding specific status codes is key to debugging. For instance, a 400 Bad Request often signals a problem with the data you sent. Or maybe a 503 Service Unavailable means the API is temporarily overloaded. You can use the search and filter functions here to pinpoint the exact code and its typical causes, saving you development time.

A A 429 status code means you've hit a rate limit. Servers use this to prevent abuse or overload. You'll see it when your app sends too many requests in a short window. Check the Retry-After header in the response — it tells you exactly how many seconds to wait. Our tool lists this detail under the 4xx section. Back off, wait the specified time, then retry. For APIs, implement exponential backoff to handle this gracefully.

A Most people assume a 200 OK means everything is perfect. Not quite. A 200 can mask problems like slow page loads or broken internal logic. For example, an API might return 200 with an error message in the JSON body. Our tool helps you look beyond the code — each entry explains common pitfalls. Always check the response body alongside the status code.

A Absolutely — especially 302 redirects to external URLs. Attackers exploit open redirects to phish credentials or spread malware. Our reference lists security implications alongside each code. Check the 3xx section for guidance on validating redirect destinations. A 200 on a phishing page doesn't mean it's safe either. Use this tool as a quick sanity check when auditing endpoints during code reviews.

A Both are temporary redirects, but they carry different meanings. A 302 tells browsers the move is temporary — search engines may not transfer link equity the same way. A 307 is stricter, preserving the request method (e.g., POST stays POST). For SEO, neither passes full ranking power like a 301 does. Our tool’s 3xx section shows you exactly when to use each. If you're doing site maintenance, stick with a 302; for permanent moves, never skip the 301.

A A 502 Bad Gateway means your backend server isn't responding properly to the proxy or load balancer. During traffic spikes, this often happens when server resources get exhausted — think connection limits exceeding 250 concurrent users on a shared host. Check your server logs for timeouts or database connection pool exhaustion. Our tool's 5xx section breaks down the exact server-side causes, helping you explain to your hosting provider exactly what's failing. Pro tip: stagger your CDN's origin pull requests during high traffic.

A Both are 1xx informational codes, but they serve completely different jobs. 100 Continue means the server got your initial request headers and you should keep sending the body. 101 Switching Protocols appears when the server agrees to upgrade the connection — think WebSocket handshakes or HTTP/2 upgrades. Our tool's 1xx section explains each protocol scenario clearly. Filter by '1xx' to see them side by side. Handy tip for QA testers: if your WebSocket connection keeps dropping, verify the 101 response is being sent.

A Not necessarily. A 503 Service Unavailable often means temporary overload, like your server hitting 500 concurrent database connections. Your site might come back within minutes. Our tool’s 5xx section explains each subtype — for example, a 503 with a Retry-After header is different from one without. Check your server logs before panicking. Pro tip: configure a custom 503 page with a refresh meta tag to help users retry automatically.

A A 304 fires when your browser sends an If-Modified-Since or If-None-Match header, and the server says nothing changed. That saves a full download, but only if you're caching correctly. Check your server logs — 304s should appear alongside 200s for the same resource. If you never see them, your cache headers are off. Set Cache-Control max-age to at least 3600 seconds for static assets. Our tool's 3xx section lists the exact conditions for triggering a 304. That's where you'll spot misconfigurations fast.