304 vs 204: Not Modified vs No Content
304 and 204 can look similar in logs, but they tell clients, crawlers, and API consumers different things.
| Aspect | 304 | 204 |
|---|---|---|
| Meaning | Not Modified describes how the server processed the request and what the client should do next. | No Content describes how the server processed the request and what the client should do next. |
| Typical use case | HTTP 304 Not Modified indicates a redirection response outcome. | HTTP 204 No Content indicates a success response outcome. |
| Caching/client behavior | Check cache headers and downstream behavior for 304. | Check cache headers and downstream behavior for 204. |
| SEO implications | Search crawlers interpret 304 according to redirect-codes semantics. | Search crawlers interpret 204 according to success semantics. |
| API/backend impact | API clients may branch logic specifically on 304. | API clients may branch logic specifically on 204. |
When to use one vs the other
Use 304 when the response should communicate not modified behavior; use 204 when no content is the accurate protocol signal.
A frequent mistake is swapping 304 and 204 for convenience; that causes client retry bugs, incorrect cache signals, and misleading monitoring data.
Decision summary: if user agents should receive the Not Modified signal, return 304; if they should receive No Content, return 204.
FAQ
What is the biggest difference between 304 and 204?
304 communicates Not Modified, while 204 communicates No Content. Choosing the right one keeps clients and intermediaries predictable.
Do 304 and 204 have SEO or caching impact?
Yes. Search engines and caches interpret status classes differently. Use each code according to its semantics to avoid accidental indexing, stale responses, or crawl inefficiency.
Can APIs safely return 304 instead of 204?
Only when it matches contract semantics. API clients often branch logic by exact code, so swapping them can break retries, auth handling, or user-facing errors.
Related guides: 304 Not Modified · 204 No Content