To make it easier to experiment with priority hints (particularly for LCP images) without making production changes, I set up a couple of public Cloudflare Workers that can be used dynamically with WebPageTest to inject priority hints into existing pages and to preload arbitrary images when combined with WebPageTest's
overrideHost script command.
There is a cloudflare worker at
hint.perf.workers.dev that will take a CSS selector from the
x-hint HTTP header and add
fetchpriority=high to any elements in the HTML that match the selector. The easiest way to experiment with this is to use Chrome's dev tools locally, identify the element that hosts the imag