100 vs 103: Continue vs Early Hints
100 and 103 can look similar in logs, but they tell clients, crawlers, and API consumers different things.
| Aspect | 100 | 103 |
|---|---|---|
| Meaning | Continue describes how the server processed the request and what the client should do next. | Early Hints describes how the server processed the request and what the client should do next. |
| Typical use case | HTTP 100 Continue indicates a informational response outcome. | HTTP 103 Early Hints indicates a informational response outcome. |
| Caching/client behavior | Check cache headers and downstream behavior for 100. | Check cache headers and downstream behavior for 103. |
| SEO implications | Search crawlers interpret 100 according to informational semantics. | Search crawlers interpret 103 according to informational semantics. |
| API/backend impact | API clients may branch logic specifically on 100. | API clients may branch logic specifically on 103. |
When to use one vs the other
Use 100 when the response should communicate continue behavior; use 103 when early hints is the accurate protocol signal.
A frequent mistake is swapping 100 and 103 for convenience; that causes client retry bugs, incorrect cache signals, and misleading monitoring data.
Decision summary: if user agents should receive the Continue signal, return 100; if they should receive Early Hints, return 103.
FAQ
What is the biggest difference between 100 and 103?
100 communicates Continue, while 103 communicates Early Hints. Choosing the right one keeps clients and intermediaries predictable.
Do 100 and 103 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 100 instead of 103?
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: 100 Continue · 103 Early Hints