422 vs 424: Unprocessable Content vs Failed Dependency
422 and 424 can look similar in logs, but they tell clients, crawlers, and API consumers different things.
| Aspect | 422 | 424 |
|---|---|---|
| Meaning | Unprocessable Content describes how the server processed the request and what the client should do next. | Failed Dependency describes how the server processed the request and what the client should do next. |
| Typical use case | HTTP 422 Unprocessable Content indicates a client errors response outcome. | HTTP 424 Failed Dependency indicates a client errors response outcome. |
| Caching/client behavior | Check cache headers and downstream behavior for 422. | Check cache headers and downstream behavior for 424. |
| SEO implications | Search crawlers interpret 422 according to client-errors semantics. | Search crawlers interpret 424 according to client-errors semantics. |
| API/backend impact | API clients may branch logic specifically on 422. | API clients may branch logic specifically on 424. |
When to use one vs the other
Use 422 when the response should communicate unprocessable content behavior; use 424 when failed dependency is the accurate protocol signal.
A frequent mistake is swapping 422 and 424 for convenience; that causes client retry bugs, incorrect cache signals, and misleading monitoring data.
Decision summary: if user agents should receive the Unprocessable Content signal, return 422; if they should receive Failed Dependency, return 424.
FAQ
What is the biggest difference between 422 and 424?
422 communicates Unprocessable Content, while 424 communicates Failed Dependency. Choosing the right one keeps clients and intermediaries predictable.
Do 422 and 424 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 422 instead of 424?
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: 422 Unprocessable Content · 424 Failed Dependency