HTTP 103 — Early Hints

What 103 actually means

When a server knows a page will need a particular stylesheet or font but needs another 200 ms to build the HTML, it can send a 103 first, carrying `Link` headers with `rel=preload` or `rel=preconnect`. The browser starts fetching those assets immediately, then receives the real 200 later on the same connection. It is a performance optimisation, not an error, and it is supported by Chrome, Firefox and Safari.

Common causes

• The origin is using early hints to preload critical CSS, fonts or scripts
• A CDN such as Cloudflare or Fastly is generating early hints automatically from previous responses

If you're just trying to view the page

1. Nothing — this makes pages load faster and is invisible in normal browsing
2. If a developer tool shows a 103 followed by a 200 for the same request, that is the intended sequence, not a duplicate

If it's your site

1. Only hint at assets that are genuinely needed on every render; wrong hints waste bandwidth and can slow the page down
2. Requires HTTP/2 or HTTP/1.1 with a client that tolerates interim responses — some old proxies drop or choke on them
3. Do not put anything in a 103 that the final response might contradict; the hints are advisory and cannot be retracted

Reference

Status code

103

Reason phrase

Early Hints

Category

1xx — Informational

Defined in

RFC 8297