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Speculation Rules: from hover to an instant pageThe browser prefetches or prerenders the next page -- on click it is already thereApproachuser moves towardthe linkPrerendernext page loadsin the backgroundActivationclick reveals thefinished pageInstantly visibleLCP near zeromillisecondsEagerness: when the browser speculatesFrom cautious to instant -- more speed also means more risk of wasted prerendersconservativeonly on clickWaste: nonemoderateafter 200 ms hoverWaste: loweagerafter ~10 ms hoverWaste: mediumimmediateas soon as the ruleWaste: higher25%of mobile top-10M sitesnow use Speculation Rules(Web Almanac 2025)200 mshover before the moderatelevel speculates(Chrome for Developers)Chrome 144prerender-until-script as anew level (January 2026)(Chrome for Developers)
Frontend-Performance Jul 6, 2026

Speculation Rules: Instant Navigation via Prerendering

How the Speculation Rules API prefetches or prerenders next pages, tunes eagerness correctly, and avoids wasted prerenders and analytics side effects.

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Three Views on Speed DataLab (Lighthouse)one simulated testfixed device, fixed networkno ranking impactCrUX (field data)real Chrome users28-day window, p75Google's ranking sourceYour own RUMall browsers, liveelement and script detailshows the whyPerformance budget at the 75th percentilegoodneeds improvementpoor75th percentileLCP lab: 1.9 sLCP field p75: 3.1 slab value clean, field data breaks the budget
Performance Jul 3, 2026

RUM vs. CrUX: Using Field Data Right for Speed

Lighthouse lab scores do not affect ranking. Google rates Core Web Vitals via CrUX field data at the 75th percentile. How to use RUM, CrUX and budgets.

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fetchpriority="high": load the LCP image soonerBrowser load order without and with the priority hint on the hero imageWITHOUT fetchpriorityHTML + CSSscripts (high priority)LCP image waits (low)LCP image loads lateLCP 4.2 sWITH fetchpriority="high"HTML + CSSLCP image loads at onceLCP 1.9 s-2.3secondsLCP in test(DebugBear)4.2 s to 1.9 sThree rules for the priority hint1Exactly one elementOnly the LCP image getshigh - nothing below it.More high = nothing prioritized2Never lazy-load itloading="lazy" on the LCPimage slows it down.Load the hero image eagerly3Pair it with preloadPreload finds the image,high raises its priority.srcset stays on the img tagImages start at low priority in the browser (web.dev) - the LCP image is treated like a minor one.Use of fetchpriority for the LCP image rose to 15 percent of mobile pages (Web Almanac 2024).A declarative attribute, no new infrastructure - a quick win of frontend optimization.
Frontend-Performance Jul 1, 2026

fetchpriority: Speed Up LCP with Priority Hints

How fetchpriority='high' loads the LCP image sooner: correct use, interplay with preload and srcset, the most common mistakes and the LCP quick win.

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CLS vs. Visual Stability Index - what gets measuredCLS - the load phase onlyPage render0 to ~5 sscroll, interaction and late loading stay unaccounted forblind spot after loadVisual Stability Index - the whole visitLoadingimages, fontsScrollinglazy contentInteractionclick, filterDwell timebanners, adsintentional movements are recognised - unexpected jumps count across the whole visitintent-aware scoring instead of load phase onlyField data May 2026 (CrUX)81.3%good CLSof origins55.9%pass all threeCore Web VitalsWhat VSI captures on topshifts during scroll and lazy loadinglate-injected banners and sticky elementsmovement during interaction
Performance Jun 29, 2026

Visual Stability Index 2026: The Next CLS Step

Visual Stability Index (VSI): in 2026 Google measures layout stability across the whole visit, not just page load. How to make your website future-proof.

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Progressive Image Display: Perception vs. BytesFrom the tiny placeholder to the sharp image along the timeline0 msHTML parsed~50 msLQIP visibleloadingBlur-up fadedonesharp imageEmpty / CLS riskLQIP ~400 bytesBuilding / fadeFully resolved83.3%LCP is an image (desktop)~400 Btypical LQIP size11-15%faster perceived with feedbackReserved space via width/height + aspect-ratio = no layout shiftThe placeholder fills the box from the first millisecond, the real image fades in on top
Performance Jun 26, 2026

Progressive Image Display: LQIP and Blur-up for Speed

LQIP, blur-up and responsive images for faster image build-up: better perceived and measured performance, fewer layout shifts, strong Core Web Vitals.

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Hydration Cost: Full Hydration vs. Islands ArchitectureServer-Side Rendering (HTML generated on the server)0s1s2s3sFull HydrationJS download (entire bundle)Hydration of the whole pageMain thread blockedinteractiveIslands / partial hydrationisland JS onlyselectiveinteractiveinteractive soonerinteractive earlierTime to Interactive80%less JS possible200msTBT target mobile8.4%more conversions per 0.1sServer renderHTML firstCritical islandshydrate by priorityLazy/on demandon interactionResumabilityno re-run
Performance Jun 24, 2026

Server-Side Rendering and Hydration Done Right

SSR delivers HTML fast, but hydration costs performance. Islands, partial hydration and resumability for fast shops and strong Core Web Vitals.

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Cumulative Layout Shift - unstable vs. stable shop layoutUnstable - CLS 0.28HeaderImage without width/heightloads in lateProduct title and priceCookie banner injected lateButton shifts downwardWeb font swap shifts textAd without reserved spaceStable - CLS 0.02HeaderImage reserved via aspect-ratiospace reserved upfrontProduct title and priceButton stays in placeFont fallback metrically matchedAd slot with fixed heightOverlay as position fixedCLS thresholdsGoodMidPoor0.10.250.25+Top causesUnsized images, fontsAds, late injectionsBanners without placeholdersSession windowlargest shift burstmax 5s window1s gap per window
Performance Jun 22, 2026

Avoid Cumulative Layout Shift: Stable Shops

Avoid CLS: fix layout shifts from images, fonts, ads and injections precisely. The result is measurably more stable shop layouts with a good CLS score.

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Request timeline: with and without resource hintsConnection setup and load start for the LCP image and a fontWITHOUT hintsDNSTCPTLSLCP image loadslate startfont loadsWITH hintsDNSTCPTLSpreconnect: warm connectionLCP image loads earlyfont loads early100-500ms savedResource hint adoption (Web Almanac 2024)33%dns-prefetchof pages28%preconnectof pages19%preloadof pages6%prefetchof pages15%fetchpriorityfor LCP imagemobilepreconnect shortens connection setup by roughly 100 to 500 ms (web.dev) --use of fetchpriority for the LCP image rose from 0.03 to 15 percent of mobile pages (Web Almanac 2024).
Frontend-Performance Jun 19, 2026

Resource Hints: Using preload, prefetch and preconnect

How preload, prefetch, preconnect, dns-prefetch and priority hints shorten connection setup, speed up the LCP image and fonts -- and where over-loading hurts.

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Core Web Vitals: Same Device, Two WorldsShare of origins passing all three vitals (CrUX)MobileLCP62%largest paint slowINP77%touch responseCLS81%layout stabilityDesktopLCPOKINP97%CLSOKAll three vitals passing48%mobile56%desktopvsMobile audit simulatedCPU 4x slowerNetwork Slow 4G57%of e-commerce revenue mobile53%abandon after 3 s load48 percent of origins pass all Core Web Vitals on mobile, 56 percent on desktop (Web Almanac 2025) --around 57 percent of worldwide e-commerce revenue happens on mobile (Statista 2024).
Mobile-Performance Jun 17, 2026

Mobile Performance: Speeding Up Shops on Phones

How throttled CPU, slow networks, viewport and touch shift mobile Core Web Vitals and which levers speed up your shop on the phone where revenue happens.

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