HTTP 103 Early Hints Checker

When a visitor navigates to a dynamic website, traditional servers must query databases, invoke backend microservices, or render templates before the very first byte of HTML can be transmitted. During this TTFB delay, the visitor’s network pipe sits completely idle.

With HTTP 103 Early Hints, the server or CDN edge immediately answers with hints for the critical stylesheets, fonts, and scripts the page will need. By the time the HTML document finishes streaming, the browser has already downloaded the CSS needed to paint the screen.

HTTP/2 originally introduced Server Push with similar ambitions. However, Server Push pushed raw payloads blindly—wasting megabytes of data if the visitor already had the files in their browser cache. As a result, Chrome and Safari removed Server Push support.

Early Hints solves this flaw by delegating the download decision to the browser. The browser receives the hint, verifies its local HTTP cache, and only downloads missing assets over multiplexed connections.

You don’t necessarily need to rewrite your backend application code to take advantage of Early Hints. Edge providers like Cloudflare, Fastly, and Akamai can cache your origin’s Link headers or use machine learning to predict critical assets and dispatch 103 Early Hints directly from the edge PoP nearest your user.

Use this tool to verify whether your edge configuration is actively serving 103 responses, or if your hints are still stranded in final 200 response headers.