206 vs 304: Partial Content vs Not Modified
206 and 304 can look similar in logs, but they tell clients, crawlers, and API consumers different things.
| Aspect | 206 | 304 |
|---|---|---|
| Meaning | Partial Content describes how the server processed the request and what the client should do next. | Not Modified describes how the server processed the request and what the client should do next. |
| Typical use case | HTTP 206 Partial Content indicates a success response outcome. | HTTP 304 Not Modified indicates a redirection response outcome. |
| Caching/client behavior | Check cache headers and downstream behavior for 206. | Check cache headers and downstream behavior for 304. |
| SEO implications | Search crawlers interpret 206 according to success semantics. | Search crawlers interpret 304 according to redirect-codes semantics. |
| API/backend impact | API clients may branch logic specifically on 206. | API clients may branch logic specifically on 304. |
When to use one vs the other
Use 206 when the response should communicate partial content behavior; use 304 when not modified is the accurate protocol signal.
A frequent mistake is swapping 206 and 304 for convenience; that causes client retry bugs, incorrect cache signals, and misleading monitoring data.
Decision summary: if user agents should receive the Partial Content signal, return 206; if they should receive Not Modified, return 304.
FAQ
What is the biggest difference between 206 and 304?
206 communicates Partial Content, while 304 communicates Not Modified. Choosing the right one keeps clients and intermediaries predictable.
Do 206 and 304 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 206 instead of 304?
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: 206 Partial Content · 304 Not Modified