{"id":654,"slug":"speculation-rules-moderate-eagerness-default","title":"Speculation Rules with eagerness:\"moderate\" is the 2026 default for instant navigation; ~82% LCP improvement in CoreDash field data","kind":"reference","scope":"business","status":"current","audiences":["claude-code","candid-team"],"topics":["core-web-vitals","speculation-rules"],"reference_body":"**Claim:** Per Arjen Karel's CoreDash field data (corewebvitals.io): *\"Across sites monitored by CoreDash, prerendered navigations have a p75 LCP of 320ms compared to 1,800ms for standard navigations on the same sites. That is an 82% improvement from a single API.\"*\n\n**Confidence:** Moderate-to-high — single-source field measurement, but mechanism is well-understood and corroborated by Google Chrome team posts.\n\n**Browser support:** Chrome/Edge/Opera stable; Safari 26.2 behind a flag; Firefox positive standards position, not shipped. Covers ~70% of global traffic.\n\n**Default JSON:**\n```json\n{ \"prerender\": [{ \"where\": { \"href_matches\": \"/*\" }, \"eagerness\": \"moderate\" }] }\n```\n\n`moderate` prerenders on hover (desktop) or 50ms after a link enters the viewport (mobile, per Chrome 144 from January 2026).\n\n**Risk mitigations:**\n\n- Use `moderate` not `immediate` on most sites.\n- Exclude logout/cart-mutation/admin URLs explicitly.\n- Use the new (Chrome 144, Jan 2026) **prerender-until-script** option for pages with analytics that fire on render — fetches HTML, begins rendering, but pauses JS at the first blocking script tag.\n- **Never use GET requests for state-mutating actions** (this is true regardless of Speculation Rules, but they make the lapse exploitable in seconds).","rationale_body":null,"metadata":null,"links":{"outgoing":[{"slug":"2026-performance-budget-smb-site","title":"Reference: 2026 performance budget — SMB marketing site (Candid default targets)","kind":"reference","scope":"business","link_type":"relates-to"}],"incoming":[{"slug":"view-transitions-cross-doc-limited-no-firefox","title":"Cross-document View Transitions are Limited Availability — Chrome/Edge 126+, Safari 18.2+, Firefox not yet shipped","kind":"reference","scope":"business","link_type":"relates-to"}]},"created_at":"2026-05-22T21:24:18.310Z","updated_at":"2026-05-22T21:24:18.310Z"}