What do the HTTP status code classes mean?

1xx are informational, 2xx mean success, 3xx are redirects, 4xx are client errors (the request was wrong) and 5xx are server errors (the request was fine but the server failed).

What is the difference between 401 and 403?

401 Unauthorized means the client is not authenticated and should send credentials. 403 Forbidden means the server knows who the client is but refuses access; retrying with the same credentials will not help.

Should I use 301 or 308 for a permanent redirect?

Both are permanent. 301 lets clients change POST to GET when following the redirect, while 308 guarantees the method and body are preserved, so prefer 308 for API endpoints.

When should an API return 422 instead of 400?

Use 400 when the request is malformed, such as invalid JSON. Use 422 when the syntax is valid but the content fails validation, such as a missing required field or an out-of-range value.

How do I search for a code?

Type a full or partial code: "40" lists 400 to 409 and "5xx" lists every server error. Any other text searches names, descriptions and best practices. Press "/" to focus the search box.

HTTP Reference

The definitive reference for every HTTP status code, with examples, best practices, and instant search.

38 of 38 codes

1xx Informational

The server received the request and is continuing the process.

2xx Success

The request was received, understood, and accepted.

3xx Redirection

Further action is needed to complete the request.

4xx Client Error

The request contains bad syntax or cannot be fulfilled.

5xx Server Error

The server failed to fulfil a valid request.

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HTTP Reference FAQ

What do the HTTP status code classes mean?: 1xx are informational, 2xx mean success, 3xx are redirects, 4xx are client errors (the request was wrong) and 5xx are server errors (the request was fine but the server failed).
What is the difference between 401 and 403?: 401 Unauthorized means the client is not authenticated and should send credentials. 403 Forbidden means the server knows who the client is but refuses access; retrying with the same credentials will not help.
Should I use 301 or 308 for a permanent redirect?: Both are permanent. 301 lets clients change POST to GET when following the redirect, while 308 guarantees the method and body are preserved, so prefer 308 for API endpoints.
When should an API return 422 instead of 400?: Use 400 when the request is malformed, such as invalid JSON. Use 422 when the syntax is valid but the content fails validation, such as a missing required field or an out-of-range value.
How do I search for a code?: Type a full or partial code: "40" lists 400 to 409 and "5xx" lists every server error. Any other text searches names, descriptions and best practices. Press "/" to focus the search box.

HTTP Reference

1xx Informational

100ContinueThe server received the request headers, send the body.

101Switching ProtocolsThe server is switching to the protocol the client requested.

102ProcessingThe server is processing the request, but no response is available yet.

103Early HintsThe server sends preliminary headers while preparing the final response.

2xx Success

200OKThe request succeeded. The most common HTTP response.

201CreatedA new resource was successfully created.

202AcceptedThe request was accepted but hasn't been acted on yet.

204No ContentSuccess, but there's no body to return.

206Partial ContentReturning only part of the resource (range request).

207Multi-StatusMultiple status codes for multiple sub-requests (WebDAV).

3xx Redirection

301Moved PermanentlyThe resource has been permanently moved to a new URL.

302FoundTemporary redirect, the resource is at a different URL for now.

303See OtherRedirect to another URL using GET (typically after a POST).

304Not ModifiedThe cached version is still fresh, no body needed.

307Temporary RedirectTemporary redirect, the method and body must not change.

308Permanent RedirectPermanent redirect, the method and body must not change.

4xx Client Error

400Bad RequestThe server couldn't understand the request due to invalid syntax.

401UnauthorizedAuthentication is required but was missing or invalid.

403ForbiddenThe server understood the request but refuses to authorize it.

404Not FoundThe requested resource could not be found on the server.

405Method Not AllowedThe HTTP method is not supported for this endpoint.

408Request TimeoutThe server timed out waiting for the client's request.

409ConflictThe request conflicts with the current state of the resource.

410GoneThe resource existed before but has been permanently deleted.

413Content Too LargeThe request body is larger than the server is willing to accept.

415Unsupported Media TypeThe request body format is not supported by the server.

416Range Not SatisfiableThe server can't serve the requested byte range.

417Expectation FailedThe server can't meet the Expect header requirements.

418I'm a TeapotThe server refuses to brew coffee because it is, in fact, a teapot.

422Unprocessable ContentThe syntax is correct but the content is semantically invalid.

426Upgrade RequiredThe server requires the client to upgrade to a different protocol.

429Too Many RequestsRate limit exceeded, slow down.

451Unavailable For Legal ReasonsAccess denied due to legal restrictions (censorship, court order).

5xx Server Error

500Internal Server ErrorSomething went wrong on the server. The catch-all error.

501Not ImplementedThe server doesn't support the requested HTTP method.

502Bad GatewayThe proxy/gateway got an invalid response from the upstream server.

503Service UnavailableThe server is temporarily down (overloaded or under maintenance).

504Gateway TimeoutThe proxy didn't get a response from the upstream server in time.

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