Prerendering cross-origin iframes

this API is documented on MDN

The Supports-Loading-Mode reference page on MDN covers the full set of tokens, including prerender-cross-origin-frames, browser compatibility data, and the specification link. gendn doesn't duplicate MDN reference pages when they exist and include browser compat and spec anchors.

at a glance

why it exists

Navigational prerendering normally delays the load of all cross-origin iframes until the user activates the prerendered page (making it visible). For pages built around a "shell" architecture — where important content lives in embedded, cross-origin frames such as maps, video players, or chat widgets — that delay erases the latency benefit that prerendering was supposed to provide. The prerender-cross-origin-frames token lets those pages declare that they trust their embedded iframes enough to start loading them early.

how it works

The prerendered page (page B — the one being loaded speculatively, not the referring page A) adds the header to its HTTP response. The browser then treats cross-origin frames on B identically to same-origin frames during prerendering: document.prerendering is true inside them, and prerenderingchange fires on activation.

# Response headers for the prerendered page (page B):
Supports-Loading-Mode: prerender-cross-origin-frames

# Combine with credentialed-prerender if needed:
Supports-Loading-Mode: credentialed-prerender, prerender-cross-origin-frames

Browsers may ignore the hint under memory pressure or on low-battery devices. The iframe's own origin does not need to send anything; only the top-level prerendered page's response is checked.

browser support

see also

• MDN: Supports-Loading-Mode
• WICG Nav Speculation spec — Prerendering
• Explainer: prerendering-cross-origin-iframes.md
• Intent to Experiment: Prerendering cross-origin iframes
• chromestatus — Prerendering cross-origin iframes (5112398709129216)
• chrome-platform-showcase: Prerendering cross-origin iframes demos (when built)