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103 Early Hints: Preloading Before the Response

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103 Early Hints: using server think time for free preloading

When a browser requests a page, the server must process the request before responding: run backend logic, query databases, render templates. This server think time is typically 50–200ms where the browser sits idle.

HTTP 103 Early Hints (RFC 8297) fills this gap: the server immediately sends a preliminary 1xx response with Link: preload headers pointing to critical sub-resources. The browser starts fetching CSS, fonts, and images while the server finishes computing the HTML. By the time the 200 response arrives, the critical resources are already downloaded.

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