About HTTP Status Codes
HTTP status codes are three-digit codes returned by servers in response to requests, indicating the processing result of the request.
HTTP Status Code Categories
HTTP status codes consist of three digits. The first digit defines the response category, divided into five classes:
- 1xx (Informational): Indicates the request has been received and is being processed. These responses are temporary and inform the client of the request processing progress.
- 2xx (Success): Indicates the request was successfully received, understood, and accepted by the server. The most common is 200 OK.
- 3xx (Redirection): Indicates the client needs to take further action to complete the request, typically used for URL redirection.
- 4xx (Client Error): Indicates the client may have made an error, preventing the server from processing the request. Common example: 404 Not Found.
- 5xx (Server Error): Indicates the server encountered an error while processing the request. Common example: 500 Internal Server Error.
Common HTTP Status Codes
- 200 OK: Request succeeded, server has successfully processed the request
- 301 Moved Permanently: Permanent redirect, the requested resource has been permanently moved to a new location
- 302 Found: Temporary redirect, the requested resource temporarily responds from a different URI
- 400 Bad Request: Client request error, server cannot understand
- 401 Unauthorized: Request requires user authentication
- 403 Forbidden: Server refuses to execute the request
- 404 Not Found: Server cannot find the requested resource
- 500 Internal Server Error: Server internal error
- 502 Bad Gateway: Gateway or proxy server received invalid response from upstream server
- 503 Service Unavailable: Server is temporarily unavailable, usually due to overload or maintenance
FAQ
Q: Is the HTTP Status Codes Reference free?
A: Completely free, no registration required, no usage limits. Just open the webpage and use it. All data is loaded locally in your browser for fast response.
Q: How many HTTP status codes are there?
A: HTTP status codes range from 100-599, giving 500 possible codes. However, only a subset are standard-defined, while many are reserved or used by specific services. This tool includes all standard and commonly used HTTP status codes.
Q: What is the difference between 404 and 403?
A: 404 Not Found means the server cannot find the requested resource, i.e., the resource does not exist. 403 Forbidden means the server understands the request but refuses to execute it, i.e., the resource exists but you don't have permission to access it. Simply put: 404 is "not found", 403 is "not allowed".
Q: What causes a 500 error?
A: 500 Internal Server Error indicates a server internal error, a generic error status. Possible causes include: program code errors, database connection failures, server configuration errors, insufficient memory, etc. The specific cause requires checking server logs.
Q: What is the difference between 301 and 302?
A: 301 is a permanent redirect, indicating the resource has permanently moved to a new address, and search engines will update their indexes. 302 is a temporary redirect, indicating the resource temporarily responds from another address, and search engines will not update their indexes. 301 is recommended for SEO scenarios.
Q: What is a 206 status code?
A: 206 Partial Content means the server successfully processed a partial GET request, commonly used for resumable downloads or segmented download scenarios. The client requests partial content via the Range header, and the server returns a 206 status code with data within the requested range.
Q: Will new status codes be added?
A: Yes. The HTTP standard continues to evolve, and the IETF publishes new RFC documents to define new status codes. For example, 429 Too Many Requests was added later. This tool will continue to be updated to include the latest standard status codes.