HTTP Status Code Dictionary
Search and browse all HTTP status codes (200, 404, 502) with practical explanations and comparison tables.
| Class | Meaning | Example codes | Whose fault is it? |
|---|---|---|---|
| 1xx | Informational — Request received, continuing process | 100, 101 | Rarely seen (protocol negotiation) |
| 2xx | Success — Request successfully processed | 200, 201, 204 | No issues |
| 3xx | Redirection — Further action needed | 301, 302, 304 | Server configuration (directly impacts SEO) |
| 4xx | Client Error — Request cannot be fulfilled | 400, 401, 403, 404, 429 | Client side (address, authentication, format) |
| 5xx | Server Error — Server failed to fulfill request | 500, 502, 503, 504 | Server side (server, gateway) |
| Comparison | Difference | When to use which |
|---|---|---|
| 301 vs 302 | Permanent vs. Temporary Redirect | Use 301 if the address has permanently moved (search engines transfer link equity to the new address). Use 302 for temporary situations like maintenance or A/B testing. |
| 301 vs 308 | Method change allowed or not | 301/302 might change POST to GET. To preserve the method and body, use 308 (permanent) or 307 (temporary). |
| 401 vs 403 | "Unknown identity" vs. "Known, but forbidden" | Use 401 if login is required. Use 403 if logged in but unauthorized. |
| 404 vs 410 | Not found vs. Permanently gone | Use 404 if simply not found. Use 410 if intentionally removed and won't return (removed from indexes faster). |
| 400 vs 422 | Syntax error vs. Semantic error | Use 400 if the JSON itself is malformed. Use 422 if the format is correct but values violate rules. |
| 502 vs 504 | Bad response vs. No response | Use 502 if the upstream (backend) is dead or returns an invalid response. Use 504 if no response within the timeout period. |
| 503 vs 500 | Temporary vs. Internal Error | Use 503 (with Retry-After header) if temporarily unavailable due to maintenance or overload. Use 500 for internal server issues like code exceptions. |
What is the HTTP Status Code Dictionary?
Stumped by a 404 Not Found or 502 Bad Gateway? This HTTP status code dictionary is an essential reference for developers, SEO specialists, and server admins. Instantly look up any code from 100 to 511 to find its official name, a simple summary, and a practical explanation of when to use it. Search by keyword like 'redirect' or 'cache', focus on essentials with the "Common codes" filter, and click any code number to copy it. Detailed tables also clarify the crucial differences between confusing pairs like 301 vs. 302 and 401 vs. 403. A free, comprehensive guide that runs right in your browser.
How to use
- Type a code, name, or keyword like '404', 'redirect', or 'auth' into the search box.
- The list updates in real time to show all matching status codes.
- Filter the list by class (`1xx`–`5xx`) or click the `"Common codes"` button to focus on the essentials.
- Read the detailed explanation for each code, including its practical use and the relevant RFC spec.
- Click any code number in the list (e.g., `404`) to copy it to your clipboard.
- Review the "Confusing codes compared" table at the bottom to clarify subtle but important differences.
Frequently asked questions
What is the difference between 301 and 302 redirects?
301 is a permanent move, telling search engines to transfer link equity. Use it for new domains. 302 is temporary, for maintenance or testing, and keeps the original URL indexed.
How are 401 Unauthorized and 403 Forbidden different?
401 means 'who are you?'—the system requires login and authentication has failed or is missing. 403 means 'I know you, but you can't come in'—the user is logged in but lacks permission.
What's the difference between 502 Bad Gateway and 504 Gateway Timeout?
A 502 error means a backend server sent back an invalid or broken response. A 504 error means the backend was too slow and didn't respond in time. Think of it as 'broken' vs. 'slow'.
Can I search for more than just code numbers?
Yes. You can search by code number (`404`), official name (`Not Found`), or keywords related to its meaning or use, like `redirect`, `cache`, or `authentication`.