401 vs 407: Unauthorized vs Proxy Authentication Required
401 and 407 can look similar in logs, but they tell clients, crawlers, and API consumers different things.
| Aspect | 401 | 407 |
|---|---|---|
| Meaning | Unauthorized describes how the server processed the request and what the client should do next. | Proxy Authentication Required describes how the server processed the request and what the client should do next. |
| Typical use case | HTTP 401 Unauthorized indicates a client errors response outcome. | HTTP 407 Proxy Authentication Required indicates a client errors response outcome. |
| Caching/client behavior | Check cache headers and downstream behavior for 401. | Check cache headers and downstream behavior for 407. |
| SEO implications | Search crawlers interpret 401 according to client-errors semantics. | Search crawlers interpret 407 according to client-errors semantics. |
| API/backend impact | API clients may branch logic specifically on 401. | API clients may branch logic specifically on 407. |
When to use one vs the other
Use 401 when the response should communicate unauthorized behavior; use 407 when proxy authentication required is the accurate protocol signal.
A frequent mistake is swapping 401 and 407 for convenience; that causes client retry bugs, incorrect cache signals, and misleading monitoring data.
Decision summary: if user agents should receive the Unauthorized signal, return 401; if they should receive Proxy Authentication Required, return 407.
FAQ
What is the biggest difference between 401 and 407?
401 communicates Unauthorized, while 407 communicates Proxy Authentication Required. Choosing the right one keeps clients and intermediaries predictable.
Do 401 and 407 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 401 instead of 407?
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: 401 Unauthorized · 407 Proxy Authentication Required