406 vs 415: Not Acceptable vs Unsupported Media Type
406 and 415 can look similar in logs, but they tell clients, crawlers, and API consumers different things.
| Aspect | 406 | 415 |
|---|---|---|
| Meaning | Not Acceptable describes how the server processed the request and what the client should do next. | Unsupported Media Type describes how the server processed the request and what the client should do next. |
| Typical use case | HTTP 406 Not Acceptable indicates a client errors response outcome. | HTTP 415 Unsupported Media Type indicates a client errors response outcome. |
| Caching/client behavior | Check cache headers and downstream behavior for 406. | Check cache headers and downstream behavior for 415. |
| SEO implications | Search crawlers interpret 406 according to client-errors semantics. | Search crawlers interpret 415 according to client-errors semantics. |
| API/backend impact | API clients may branch logic specifically on 406. | API clients may branch logic specifically on 415. |
When to use one vs the other
Use 406 when the response should communicate not acceptable behavior; use 415 when unsupported media type is the accurate protocol signal.
A frequent mistake is swapping 406 and 415 for convenience; that causes client retry bugs, incorrect cache signals, and misleading monitoring data.
Decision summary: if user agents should receive the Not Acceptable signal, return 406; if they should receive Unsupported Media Type, return 415.
FAQ
What is the biggest difference between 406 and 415?
406 communicates Not Acceptable, while 415 communicates Unsupported Media Type. Choosing the right one keeps clients and intermediaries predictable.
Do 406 and 415 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 406 instead of 415?
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: 406 Not Acceptable · 415 Unsupported Media Type