Speculation rules: mobile "eager" eagerness improvements

concepts

1. Mobile Eager Tuning

   Live: inject a real speculationrules script, scroll links into view, and log when prerender activates. Switch eagerness and prefetch/prerender on the fly.

2. Viewport dwell

   What specifically changed in v143: scrub the dwell threshold and watch links activate as they stay in view long enough. The mechanism behind mobile "eager".

3. Eagerness comparator

   All four eagerness modes side by side with live link probes, mode pickers, and an interaction log that explains exactly which trigger each mode would have used for the event you just performed.

4. Mobile Budget Optimizer

   A three-card device profile picker (low/mid/high-end) updates a budget table with max prefetches, max prerenders, bandwidth threshold, and slot counts per eagerness level. Enter URLs with estimated sizes, then generate a tiered speculationrules JSON blob with correct eagerness per device profile — with a live cost calculator showing bandwidth savings vs always-eager.

why it shipped

On mobile, "eager" eagerness speculation rules prefetches and prerenders now trigger when HTML anchor elements are in the viewport for a short time.

references

• ChromeStatus entry
• Spec