Early Hints
1xx Informational
Last updated:
The server sends preliminary response headers before the final response, typically Link headers for resource preloading.
Description
Allows the browser to start preloading resources (CSS, JS, fonts) while the server is still generating the main HTML response. Supported by Chrome, Fastly, and many CDNs.
When to use
Use 103 to send `Link: rel=preload` headers on slow server-rendered pages. Can noticeably improve LCP on complex apps.
Specification
RFC 8297
Examples
HTTP response
HTTP/1.1 103 Early Hints
Content-Type: application/json
{"error":"Early Hints"}Node.js (Express)
res.status(103).json({ error: "Early Hints" });Go (net/http)
w.WriteHeader(http.Status103)
Python (Flask)
return jsonify({"error": "Early Hints"}), 103