HTTP reference / Status codes

HTTP status codes, explained for API builders and debuggers

Browse the meaning of HTTP status codes from 100 Continue through 511 Network Authentication Required, with links to detailed pages for common API errors.

Try a status code Send a request

codes://http-reference59 codes

200OK 301Moved Permanently 404Not Found 429Too Many Requests 502Bad Gateway 503Service Unavailable

definitionheadersretrydebug path

Reference hub

Start with the class, then inspect the exact code.

The first digit tells you the broad outcome. The exact code tells you what a client, proxy, cache, monitor, retry policy, or API test should do next.

1xx

Informational

The request was received and processing continues.

100Continue 101Switching Protocols 103Early Hints

2xx

Success

The request was accepted, processed, or fulfilled.

200OK 201Created 202Accepted 204No Content 206Partial Content

3xx

Redirection

The client needs another request or cached representation.

301Moved Permanently 302Found 303See Other 304Not Modified 307Temporary Redirect 308Permanent Redirect

4xx

Client error

The request cannot be completed as sent by the client.

400Bad Request 401Unauthorized 403Forbidden 404Not Found 405Method Not Allowed 409Conflict 410Gone 422Unprocessable Entity 429Too Many Requests 451Unavailable For Legal Reasons

5xx

Server error

The server or an upstream dependency failed to complete the request.

500Internal Server Error 501Not Implemented 502Bad Gateway 503Service Unavailable 504Gateway Timeout 511Network Authentication Required

Common API codes 200 OK 201 Created 204 No Content 301 Moved Permanently 302 Found 304 Not Modified 400 Bad Request 401 Unauthorized 403 Forbidden 404 Not Found 409 Conflict 422 Unprocessable Entity 429 Too Many Requests 500 Internal Server Error 502 Bad Gateway 503 Service Unavailable 504 Gateway Timeout

Working reference

What goes in, what comes out, and what the result can prove.

INPUTHTTP response status plus request context

OUTPUTSemantics, cache/retry implications and related testing paths

Concrete artifact

A status code is only one part of the response

429 Too Many Requests
Retry-After: 30
Cache-Control: private, no-store
Body: stable machine-readable error code
Client check: honor delay and cap attempts

Review sequence

Three checks before the result becomes a decision.

Semantics

Interpret the code using the HTTP method and response headers.

Client behavior

Decide whether to retry, redirect, authenticate or stop.

Reproduction

Use a mock or playground to verify handling.

Limits

What this workflow does not prove.

Application-specific error codes still belong in the response body.
Intermediaries can alter redirects, caching and authentication behavior.
The same status can require different handling for safe and unsafe methods.

Questions worth answering

Before you put it into a real workflow.

What are HTTP status codes?

They are three-digit response codes sent by a server to summarize how an HTTP request was handled.

Which codes matter most for APIs?

Common API workflows frequently depend on 200, 201, 204, 301, 302, 400, 401, 403, 404, 409, 422, 429, 500, 502, 503, and 504.

Can I test a code from this page?

Yes. Use the status playground, HTTP client, or mock server to create and inspect real responses for the code you are studying.

Next move

Start with one concrete API problem.

Keep the first step small. Move into a workspace when the result deserves to be saved, repeated, or shared.

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