Status Class
4xx Client Error
Client-side request issues such as invalid syntax, missing resources, or permission failures.
400 Bad Request
Learn what 400 Bad Request means when servers reject malformed requests. Understand common causes like invalid JSON, missing parameters, and how to debug.
HTTP 401 Unauthorized: Authentication Required
Learn what 401 Unauthorized means, why it happens, and how to fix authentication errors. Complete guide with examples for APIs and web applications.
402 Payment Required
Reserved for future use in digital payment systems. Learn about this experimental status code and modern payment verification alternatives.
HTTP 403 Forbidden: Access Denied
Learn what 403 Forbidden means, why access is denied, and how to fix permission errors. Complete guide with examples for APIs and web applications.
HTTP 404 Not Found: What It Means and How to Fix It
Learn what a 404 Not Found error means, why it happens, and how to fix it. Complete guide with examples for developers and users.
405 Method Not Allowed
Learn what 405 Method Not Allowed means when HTTP methods are rejected. Understand the Allow header, proper API design, and how to handle method restrictions.
406 Not Acceptable
The server cannot produce a response matching the client's Accept headers. Learn about content negotiation and how to handle format mismatches.
408 Request Timeout
Learn what 408 Request Timeout means when servers close idle connections. Understand timeout causes, client retry strategies, and connection management.
409 Conflict
Learn what 409 Conflict means when requests conflict with server state. Understand concurrent updates, version conflicts, and optimistic locking strategies.
410 Gone
Learn what 410 Gone means and when resources are permanently removed. Understand the difference between 410 and 404, and SEO implications for deleted content.
412 Precondition Failed
The server doesn't meet one or more preconditions specified in request headers. Learn about conditional requests and how to prevent conflicts.
413 Payload Too Large
The request body is too large for the server to process. Learn about size limits and how to handle large uploads.
414 URI Too Long
The requested URI exceeds the server's maximum length limit. Learn about URI length limits and how to handle oversized requests.
415 Unsupported Media Type
The server doesn't support the media type of the request. Learn about Content-Type headers and format requirements.
422 Unprocessable Entity
Learn what 422 Unprocessable Entity means for semantically invalid requests. Understand validation errors, the difference from 400, and proper error handling.
423 Locked
The resource is locked and cannot be accessed or modified. Learn about WebDAV locks and how to handle locked resources.
426 Upgrade Required
The server refuses to perform the request using the current protocol and requires the client to upgrade to a different protocol.
428 Precondition Required
The server requires the request to be conditional. Learn when to use 428 Precondition Required to prevent lost updates and race conditions.
HTTP 429 Too Many Requests: Rate Limiting
Learn what 429 Too Many Requests means, how rate limiting works, and how to handle API throttling in your applications.
431 Request Header Fields Too Large
The server refuses to process the request because header fields are too large. Learn how to handle and prevent 431 errors in your applications.
451 Unavailable For Legal Reasons
The requested resource is unavailable due to legal demands. Learn about 451 status code used for censorship and content blocking.
Explore Other Status Classes
1xx Informational
Interim responses that indicate request progress before a final response is sent.
2xx Success
Responses indicating the request was accepted and processed successfully.
3xx Redirection
Responses that tell clients to perform additional actions, usually by following a new URL.
5xx Server Error
Server-side failures where the request was valid but the server could not complete it.