HTTP status codes / 1xx — Informational
103 Early Hints
Preload hints sent before the final response.
What it means
Lets a server send Link headers (preload/preconnect) while it is still preparing the real response, so browsers can start fetching critical assets early. Increasingly common behind CDNs like Cloudflare.
Common causes
- CDN/origin sending preload Link headers before the final response (common behind Cloudflare/Fastly)
Reproduce it in cURL
curl -i https://early-hints.fastlylabs.com/
Same request, no terminal: paste this into the cURL converter for native code, or straight into ReqPad on your phone.
How to debug it
Some HTTP clients surface 103 as a separate event before the final status — make sure your client does not treat it as the final response.
The fastest way to pin down a 103 is to reproduce the exact request and inspect what actually went over the wire — status, headers, timing and body, without your app code in the way. That is what an API client is for; ReqPad does it from your phone, with every request saved to history.
Related codes
100 Continue · 101 Switching Protocols · 102 Processing — or the full reference.
Reproduce that 103 in 10 seconds.
Build the request, send it, read status + headers + timing — on your iPhone. Free to start.