Understanding HTTP Status Codes: What Each Range Actually Means

Most status codes get treated as background noise until something breaks - but the specific number a server returns changes how browsers, crawlers, and scripts all behave, often in ways that aren't obvious until you've been burned by the wrong one.

2xx - Success

200 OK is the only one most people think about, but the range has nuance: 201 Created confirms a new resource was made (common after a form POST), 204 No Content confirms success with deliberately nothing to return.

3xx - Redirection

• 301 Moved Permanently - tells search engines to transfer ranking signals to the new URL. Use this for real, permanent moves.
• 302 Found - a temporary redirect; search engines keep indexing the original URL. Using 302 for a permanent move is a common SEO mistake that leaves ranking signals stranded on the old URL.
• 304 Not Modified - tells a browser its cached version is still valid, saving a full re-download.

4xx - Client Errors

• 404 Not Found - the resource genuinely doesn't exist. A real 404 status matters for SEO - a "soft 404" (a not-found page that returns 200) confuses crawlers into indexing dead content.
• 401 Unauthorized vs 403 Forbidden - 401 means "authenticate to proceed," 403 means "you're identified, and still not allowed." Mixing these up gives users (and API consumers) the wrong signal about what to do next.
• 429 Too Many Requests - the correct response for rate limiting, ideally paired with a Retry-After header so well-behaved clients know when to try again.

5xx - Server Errors

A 5xx means the server itself failed to handle a valid request - as distinct from a 4xx, which means the request itself was the problem. Returning 500 for what's actually a client error (or vice versa) misleads both monitoring dashboards and the client's own retry logic - a client typically shouldn't blindly retry a 4xx, but often should retry a 5xx.

Why This Matters Beyond Correctness

Search engines use status codes as a primary signal for how to treat a URL going forward - the wrong code on a redirect, error page, or removed resource can leave stale or duplicate content indexed for far longer than intended, independent of anything else about the page's actual content.