Response Code

I. 1xx: Informational

Indicates that the request has been received and is being processed. These status codes are rarely used directly in business scenarios.

Status Code	Name	Meaning
100	Continue	The client can continue sending the request body
101	Switching Protocols	Protocol switching (e.g., HTTP → WebSocket)
102	Processing	Server is processing the request (WebDAV)

Common scenarios: WebSocket, HTTP Upgrade

II. 2xx: Success

Indicates that the request has been successfully processed.

Status Code	Name	Meaning
200	OK	Request succeeded
201	Created	Resource successfully created (POST)
202	Accepted	Request accepted, processed asynchronously
204	No Content	Success with no response body
206	Partial Content	Partial content or breakpoint download

Common scenarios: Normal API responses, file downloads, successful proxy forwarding

III. 3xx: Redirection

Indicates that further action is required to complete the request.

Status Code	Name	Meaning
301	Moved Permanently	Permanent redirection
302	Found	Temporary redirection
303	See Other	Redirect to GET
304	Not Modified	Cache is still valid
307	Temporary Redirect	Temporary redirect (method unchanged)
308	Permanent Redirect	Permanent redirect (method unchanged)

Common scenarios: CDN, HTTP → HTTPS redirection, cache control

IV. 4xx: Client Error

Indicates that there is a problem with the request.

Status Code	Name	Meaning
400	Bad Request	Invalid request format
401	Unauthorized	Not authenticated (missing token)
403	Forbidden	Authenticated but no permission
404	Not Found	Resource does not exist
405	Method Not Allowed	Method not supported
408	Request Timeout	Request timed out
409	Conflict	Resource conflict
413	Payload Too Large	Request body too large
414	URI Too Long	URL too long
429	Too Many Requests	Rate limited

● 401 / 403: Authentication failure ● 404: Target server does not exist ● 429: IP or user rate limiting

V. 5xx: Server Error

Indicates that the server failed to process the request.

Status Code	Name	Meaning
500	Internal Server Error	Internal server error
502	Bad Gateway	Invalid upstream server
503	Service Unavailable	Service unavailable
504	Gateway Timeout	Upstream timeout
507	Insufficient Storage	Insufficient storage