demo · v138

Eagerness comparison

Speculation rules has four eagerness levels. Chrome 138 improves moderate on mobile — hover is less useful on touch screens, so moderate now also arms on pointerdown. Simulate user events below and watch which levels arm in time.

Level Desktop trigger Mobile trigger (138+) Typical delay Typical hit rate
conservative pointerdown + pause pointerdown + pause ~100–200 ms High — user has committed
moderate mouseover (hover) pointerdown (138+) ~200–400 ms Medium — hover intent
eager link added to DOM link added to DOM ~50–100 ms Lower — speculative
immediate as soon as possible as soon as possible < 50 ms Lowest — unconditional

interactive simulation

conservative
trigger: pointerdown
delay: ~150 ms
idle
moderate
trigger: hover / pointerdown*
delay: ~300 ms
idle
eager
trigger: link in DOM
delay: ~75 ms
idle
immediate
trigger: rule parsed
delay: < 50 ms
idle
Simulated link — interact with it
hover or tap/click the link
readyInteract with the link above to fire speculation events…

the speculation rules JSON

<script type="speculationrules">
{
  "prefetch": [
    {
      "source": "list",
      "urls": ["/next-page"],
      "eagerness": "moderate"
    }
  ]
}
</script>

<!-- On mobile, Chrome 138+ arms "moderate" on pointerdown,
     not just mouseover. This gives mobile users the same
     prefetch benefit desktop users get from hover. -->

see also