103 Early Hints

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.