304

Not Modified

3xx Redirection

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Server perspective

Use 304 for conditional GET or HEAD requests when the client's cached representation is still current.

When to use

  • •Return 304 when If-None-Match or If-Modified-Since validates successfully
  • •Use it to save bandwidth for unchanged cacheable resources

How to respond

  • •Do not include a response body
  • •Include the cache-related metadata headers the client needs to update its stored response

Headers to consider

  • •Date
  • •ETag
  • •Last-Modified
  • •Cache-Control
  • •Expires
  • •Vary
  • •Content-Location

Response body

  • •Do not include a response body in a 304 response.

Server-side pitfalls

  • •Do not return 304 for unconditional requests
  • •Return 200 with the representation when the resource changed

Examples

ETag cache validation

Request:GET /assets/app.js with If-None-Match: "abc123"
Response:304 Not Modified with no body

The server confirms the cached asset is still valid.

References

Related 3xx Redirection Codes

300

Multiple Choices

There are several valid versions of this thing, and the server is asking you to pick one.

301

Moved Permanently

This moved for good. Start using the new address from now on.

302

Found

Go somewhere else for now, but don’t assume this new address is the permanent one.

303

See Other

You submitted something successfully. Now go fetch this other page to see the result.

305

Use Proxy

This is an old HTTP idea that said, 'Use this proxy instead,' but modern systems should not rely on it.

306

Unused

This number exists in the HTTP list, but it does not mean anything you should use in a real app today.

307

Temporary Redirect

Go to this other address for now, and send the exact same kind of request there.

308

Permanent Redirect

This moved for good, and you should keep using the same kind of request when you switch to the new address.