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HTTP Status Codes Reference

In-depth guides for the most common HTTP status codes. Each page explains what the code means, common causes, practical troubleshooting steps, code examples, and related tools.

2xx

Success

Success responses indicate that the client's request was received, understood, and accepted.

200
OK
The standard success response. The request has succeeded and the server returned the requested resource or result.
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201
Created
A new resource was successfully created. Typically returned after POST requests with a Location header pointing to the new resource.
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3xx

Redirection

Redirection responses tell the client it needs to take additional action to complete the request, usually following a URL in the Location header.

301
Moved Permanently
The URL has permanently changed. Search engines transfer link equity to the new URL. Essential for domain migrations and HTTPS upgrades.
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302
Found
Temporary redirect. The original URL remains canonical. Used for A/B tests, login flows, and geo-based routing.
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304
Not Modified
The cached version is still valid. Saves bandwidth by telling the client to reuse its cached copy via ETag or Last-Modified validation.
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4xx

Client Errors

Client error responses indicate that the request contains bad syntax, invalid credentials, or otherwise cannot be fulfilled by the server.

400
Bad Request
The server cannot process the request due to malformed syntax. Common with invalid JSON, missing parameters, or corrupt cookies.
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401
Unauthorized
Authentication is required. The request lacks valid credentials — token missing, expired, or invalid. Not to be confused with 403.
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403
Forbidden
Access denied. The server knows who you are but you do not have permission. Often caused by file permissions, WAF rules, or role restrictions.
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404
Not Found
The most recognized HTTP error. The URL does not match any resource on the server. Often fixable with 301 redirects for moved pages.
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405
Method Not Allowed
Wrong HTTP method for this resource. You sent POST when only GET is supported, or DELETE when the resource is read-only.
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429
Too Many Requests
Rate limited. You sent too many requests too quickly. Handle with exponential backoff and respect the Retry-After header.
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5xx

Server Errors

Server error responses indicate that the server failed to fulfill a valid request. The problem is on the server side, not the client.

500
Internal Server Error
Generic server failure. Something went wrong but the server cannot be specific. Debug via error logs — the answer is always there.
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502
Bad Gateway
The proxy/gateway received an invalid response from the upstream server. Usually means the backend crashed or is not running.
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503
Service Unavailable
The server is temporarily unable to handle requests. Used during maintenance, overload, or deployment. Always temporary.
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504
Gateway Timeout
The upstream server did not respond in time. Caused by slow queries, long-running operations, or network issues between servers.
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