HTTP Status Codes
Today, let’s talk about the topic of HTTP status codes! Whether you are a beginner or an experienced developer, HTTP status codes are an essential knowledge point that you must master! They can help you solve problems and improve your website’s performance and user experience. Are you ready? Let’s dive in!
Classification of Status Codes
HTTP status codes are divided into five categories, covering the complete process from informational responses to server errors:
- • 1xx (Informational Response): The request has been received and needs further processing. (#1xx Informational Response)
- • 2xx (Success): The request has been successfully processed. (#2xx Success)
- • 3xx (Redirection): Further action is required (e.g., redirection) to complete the request. (#3xx Redirection)
- • 4xx (Client Error): There is a syntax error in the request or insufficient permissions. (#4xx Client Error)
- • 5xx (Server Error): The server failed to process the request. (#5xx Server Error)
1xx Informational Response
| Status Code | Description | Example Scenario |
| 100 | Continue | The client should continue sending the request body |
| 101 | Switching Protocols | Protocol switch (e.g., upgrade to WebSocket) |
| 102 | Processing | WebDAV extension, indicating that the request is being processed |
2xx Success
| Status Code | Description | Example Scenario |
| 200 | OK | The request was successful (e.g., webpage loaded or API returned data) |
| 201 | Created | Resource created successfully (e.g., user registration) |
| 202 | Accepted | The request has been accepted but not yet processed (asynchronous operation) |
| 203 | Non-Authoritative | Non-authoritative information, the service successfully processed the request, but the information comes from another source |
| 204 | No Content | The request was successful but there is no content returned (e.g., DELETE request) |
| 205 | Reset Content | Reset content, the service successfully processed the request with no content returned |
| 206 | Partial Content | Partial content response (supports resuming downloads) |
| 207 | Multi-Status | WebDAV multi-status response (in XML format) |
| 208 | Already Reported | WebDAV extension, the resource status has already been reported |
3xx Redirection
| Status Code | Description | Example Scenario |
| 301 | Moved Permanently | The resource has been permanently redirected (update bookmarks) |
| 302 | Found | The resource has been temporarily redirected (browser defaults to GET) |
| 303 | See Other | Forces the use of the GET method to access the new URI |
| 304 | Not Modified | Not modified, the webpage has not changed since the last request |
| 307 | Temporary Redirect | Temporary redirection while maintaining the original request method |
| 308 | Permanent Redirect | Permanent redirection while maintaining the original request method |
4xx Client Error
| Status Code | Description | Example Scenario |
| 400 | Bad Request | Request syntax error (e.g., JSON format error) |
| 401 | Unauthorized | Unauthenticated (requires login or token) |
| 402 | Payment Required | Payment required for access (digital payment scenario) |
| 403 | Forbidden | No permission to access (e.g., IP blocked) |
| 404 | Not Found | The resource does not exist (path error or deleted) |
| 405 | Method Not Allowed | HTTP method not supported (e.g., POST disabled) |
| 406 | Not Acceptable | Not acceptable, the requested content characteristics cannot respond to the requested webpage |
| 408 | Request Timeout | Request timeout, the server timed out waiting for the request |
| 409 | Conflict | Conflict, the server encountered a conflict while processing the request |
| 410 | Gone | The resource has been permanently deleted (requires 301 redirection) |
| 429 | Too Many Requests | Request rate too high (rate limiting triggered) |
| 451 | Unavailable For Legal Reasons | Unavailable for legal reasons |
Sub-status Code Extensions (for example, in IIS):
- • 401.1: Login failed (incorrect password)
- • 403.1: Insufficient execution permissions (e.g., script directory permissions)
- • 404.1: Port access is blocked
5xx Server Error
| Status Code | Description | Example Scenario |
| 500 | Internal Server Error | General server error (code exception or configuration issue) |
| 501 | Not Implemented | Request method not implemented (e.g., PATCH not supported) |
| 502 | Bad Gateway | The gateway/proxy server received an invalid response |
| 503 | Service Unavailable | Service unavailable (overloaded or undergoing maintenance) |
| 504 | Gateway Timeout | Gateway timeout (upstream server did not respond) |
| 505 | HTTP Version Error | HTTP version not supported, the server does not support the requested protocol version |
| 507 | Insufficient Storage | Insufficient storage space (WebDAV scenario) |
| 511 | Network Authentication Required | Network authentication required (e.g., public Wi-Fi login) |
Sub-status Code Extensions (specific to IIS):
- • 500.12: Application restarting
- • 503.18: Application pool configuration error
Special Status Codes
| Status Code | Description | Example Scenario |
| 418 | I’m a teapot | April Fools’ Day joke (RFC 2324) |
| 499 | Client Closed Request | The client actively closed the connection (Nginx extension) |
Summary and Recommendations
- • Error Handling:
- • 4xx errors require checking client request parameters, permissions, and caching strategies.
- • 5xx errors require checking server logs, load, and dependent services.
- • Debugging Tools: Use browser developer tools (Network tab) to view status codes in real-time.