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HTTP Status Code
304 Not Modified
RedirectionThe resource has not changed, so the client can use its cached version.
HTTP status code reference, response example, common causes, fixes, and related status codes.
What does HTTP 304 Not Modified mean?
HTTP 304 Not Modified is a status code sent by a server to indicate the result of an HTTP request.
Status codes help browsers, APIs, apps, and backend systems understand whether a request succeeded, failed, was redirected, or needs additional action.
In practice, HTTP 304 Not Modified usually appears when a server responds under specific request, validation, permission, or infrastructure conditions.
Response example
HTTP/1.1 304 Not Modified
HTTP example
HTTP/1.1 304 Not Modified
Relevant headers
ETag
ETag: "abc123"
If-None-Match
If-None-Match: "abc123"
Common causes
- Browser cache validation
- ETag or Last-Modified match
- Conditional GET request
How to fix it
- Check ETag and Last-Modified headers
- Verify cache-control logic if content should refresh
Common mistakes
- Assuming the status code alone explains the full backend issue
- Ignoring related response headers that add important context
- Treating temporary errors as permanent failures
- Retrying too aggressively without checking the cause
- Debugging the frontend only when the problem is server-side
How browsers and APIs use it
Browsers, APIs, and backend services use HTTP status codes to understand the outcome of a request. Depending on the status code, an application may render content, retry a request, redirect the user, show an error, or trigger a different flow in the client or server.
Developer note
HTTP 304 improves performance by avoiding unnecessary downloads. It is a normal part of browser caching behavior.