Third-Party Tags and INP: GTM, Chat and Consent, Measured
Third-party scripts are the usual cause of failing INP. How to measure what each tag costs on interaction, which hurt most, and how to load them for less.
Writing
Core Web Vitals: what we have had to fix
52 write-ups from production, newest first. Each one is a problem hit on a real project and how it was diagnosed and fixed.
Lighthouse Green, Search Console Red: Which CWV to Trust
Why PageSpeed says your site is fast while Search Console fails it on Core Web Vitals, which data Google uses, and how to audit against the numbers that count.
Twenty Audits Later: The Ten Fixes That Delivered Most
Across twenty Core Web Vitals engagements, ten fixes accounted for most of the improvement. What they were, how often each applied, and the order to try them.
Session Replay and Analytics SDKs: The INP Tax
Sentry Replay, Hotjar, FullStory and heavy analytics SDKs record every interaction, which costs every interaction. How to measure their share and defer them.
Real-User Monitoring That Survives Ad Blockers
Field Core Web Vitals data you own: the web-vitals library, a first-party endpoint blockers do not block, what to store, and p75 by page group.
A JavaScript Budget for a Marketing Site, Enforced in CI
How much JavaScript a marketing site should ship, how to set a budget per route, and how to fail the build when a dependency or a tag pushes it over.
INP in React Apps: Hydration, Third Parties, Measure First
Why React sites fail INP: hydration blocking early taps, wide re-renders, third-party scripts on the main thread. What to measure first and the fixes in order.
Fixing INP on Mobile When the Lab Shows Nothing
Desktop passes, Lighthouse is clean, Search Console says mobile INP is poor. Why the lab misses it, how to reproduce it.
Core Web Vitals: WordPress vs Next.js, What Differs
Same metrics, different failure modes. Where WordPress and Next.js sites typically fail LCP, INP and CLS, why, and what the platform does and does not decide.
CLS From Embeds: Trustpilot, Ads and Late Iframes
Review widgets, ad slots, maps and social embeds are the top cause of layout shift on business sites.
Cloudflare Rocket Loader, Polish and Mirage: When They Hurt
What Rocket Loader, Polish, Mirage, Auto Minify and Early Hints each do, when they help a legacy site, and when they break or slow a modern one.
TTFB on Managed Hosting and Edge Functions: Where Time Goes
Time to first byte sets the floor for every metric. Its components from DNS to origin, how to measure each, and what managed hosts and edge platforms get wrong.
Next.js Image Optimisation: sizes, priority, quality and LCP
Getting next/image right for LCP: the sizes attribute most sites get wrong, when to use priority, quality and format trade-offs, and the check that proves it.
LCP Images the Browser Cannot Discover, and the Preload Fix
Why some hero images start loading a second late: CSS backgrounds, JavaScript-inserted images, lazy loading on the wrong element. See the delay and fix it.
INP: Finding the Slow Interaction in Field Data
INP fails in Search Console and the lab shows nothing. How to instrument real users to find which element, event and script is slow, and report it usefully.
A Core Web Vitals Audit Report Engineers Act On: Our Format
Most performance audits are a Lighthouse export with commentary. The format we use instead: field data first, per-metric attribution, prioritised fixes, checks.
Cookie Consent Banners Without CLS or INP Cost
The consent banner is often the worst thing on a page for Core Web Vitals: it shifts layout, blocks the thread and fires every tag on Accept. Making one fast.
Bfcache: The Free Speed You Lose With One Header
The back/forward cache makes back navigation instant and lifts field metrics for free, unless something blocks it. Blockers from no-store to unload handlers.
Image Handling in WordPress: Sizes, WebP, Lazy Loading, LCP
How WordPress generates, serves and lazy-loads images, where the defaults hurt Core Web Vitals, and the configuration that gets the hero loading fast.
Mobile-First Performance Testing on a Mid-Range Android
Your laptop is lying about page speed. Why field data is dominated by mid-range phones, how to test on one or emulate it honestly, and what changes.
Critical CSS and Render-Blocking Resources, Explained
Why a page stays blank while stylesheets and scripts load, what the render-blocking audit means, and the fixes in order of return, from fewer files to inlining.
Explaining Web Performance to Clients Who Do Not Care
How to talk about page speed with a business owner without saying LCP: the metrics that mean money, the before-and-after that lands, and a one-page report.
Hunting Cumulative Layout Shift: Finding What Moves and Why
A method for tracking down layout shift: reproducing it, reading DevTools shift records, the usual suspects from fonts to widgets, and the fix for each.
FCP Regression After Enabling React Compiler in Next.js 16
First Contentful Paint regressed after turning on reactCompiler in Next.js 16? Here is why the runtime cache pushes paint and the boundary fix that recovers it.
INP Regression After Adding Cloudflare Turnstile Widget Fix
INP score tanked on mobile after adding the Cloudflare Turnstile widget? Here is why the embed script blocks interaction and the lazy-load fix that works.
iOS Safari CLS Spike From CSS aspect-ratio Fallback Fix
CLS spiking on iOS Safari only in CrUX? Here is why aspect-ratio falls back to auto on older Safari builds and the width/height pattern that holds layout.
React Compiler INP Regression in Production: Fix
React Compiler enabled on Next.js 16 and field INP regressed past 200ms? Here is why auto-memoisation pushes work post-commit and the scoped fix that lands.
CLS From Trustpilot Widget Late Load on Product Pages
Trustpilot widget pushing CLS over 0.1 on product pages? Here is the reserved-space pattern and lazy load fix that stops the layout shift on mobile devices.
LCP Regression After CSS Container Queries Migration
Migrated to CSS container queries and watched LCP jump 800ms in field data. Here is why the hero image stops being a priority paint and how to fix it.
INP Regression After React 19.2 useTransition Migration
INP field data spiking after wrapping filter handlers in useTransition? Here is why React 19.2 transitions can make INP worse and the pattern that fixes it.
INP Regression from React 19 Activity Component on Mobile
React 19 Activity component spiking INP past 300ms on mobile after a click? Here is the synchronous commit that triggers the long task and the fix that holds.
LCP CSS Background Image Not Discovered by Browser Fix
Your hero background image is the LCP but the browser only finds it after CSSOM parsing? Why fetchpriority does not help, and the preload that does.
Cloudflare Rocket Loader Breaking Next.js INP Scores Fix
Cloudflare Rocket Loader tanking INP on a Next.js site? Here is why it delays React hydration on mobile and the page rule that restores interactivity.
next/script afterInteractive Blocking INP on Mobile
next/script strategy='afterInteractive' still pushing INP past 500ms on mobile? Here is the lazyOnload, worker, and onLoad fix that drops it back under 200ms.
TTFB Spike from Vercel Middleware Geolocation Lookup
Vercel middleware doing geo redirects spiking TTFB to 800ms? Here is the runtime, header, and edge config fix that cuts it back under 100ms.
INP Regression From Sentry Session Replay 9 on Mobile
Sentry Session Replay 9 tanking INP on mobile after the upgrade? See what changed in the rrweb sampler and the config fix that pulls INP back under 200ms.
Next.js bfcache Not Restoring Page on Back Navigation Fix
Next.js page failing back/forward cache and re-rendering on browser back? Most causes are unload listeners, open WebSockets, or Cache-Control no-store.
Long Animation Frames API for Debugging INP in Production
Debugging INP regressions in 2026? Wire the Long Animation Frames API to capture the exact slow handler in real users with a working PerformanceObserver.
INP Field Data Worse Than Lighthouse Lab Score Fix
Lighthouse INP score is green but CrUX field data is failing pages in Search Console? Close the lab-vs-real-user INP gap with focused attribution fixes.
CLS From Skeleton Loaders in Suspense Fallback Fix
Cumulative Layout Shift spiking from Suspense skeleton loaders in Next.js 16? Match the skeleton dimensions to real content with a working CSS pattern.
PageSpeed LCP Different From Field Data Fix Guide
PageSpeed Insights LCP score different from CrUX field data? Fix the lab vs real-user gap with throttling, viewport, and resource priority hints.
next/image priority Not Preloading Hero: LCP Fix
next/image with priority not generating a preload link and tanking your hero LCP score? Fix the missing preload hint and PPR boundary issue with code.
Vercel Speed Insights No Data After Next.js 16: Fix
Vercel Speed Insights showing no data after Next.js 16 upgrade? Fix the missing beacon, CSP block, and the SpeedInsights component placement with code.
Cookie Consent Banner CLS Fix: Stop the Layout Shift
Cookie consent banner tanking your CLS score and Core Web Vitals on first paint? Fix the late-injected banner, reserved space, and animation timing in code.
Next.js 16 Image priority Deprecated: Real LCP Fix
Next.js 16 deprecated the priority prop on next/image. Migrate to preload, fix the LCP regression, and stop accidentally preloading every product hero image.
INP Mobile Regression from React Hydration Delay Fix
INP score worse on mobile than desktop after a React deploy? Hydration is blocking the main thread. Fix it with code splitting and Suspense streaming.
LCP Preload Hint Picking the Wrong Image: Real Fix
LCP regressed because the browser preloads the wrong image with next/image priority? Fix fetchpriority, srcset, and preload candidate selection with code.
next/font CLS Layout Shift in Next.js 16: Real Fix
next/font causing CLS layout shift in Next.js 16 after the upgrade? Fix font fallback metrics, size-adjust, and display swap settings with working code.
INP Regression from GTM Third-Party Tags in 2026
INP score regressing above 200ms after adding Google Tag Manager tags? Here is how to diagnose the blocking tag and fix it with working code.
CLS Spike from next/font Local Fallback in Next.js 16
CLS regression spiking from next/font fallback after upgrading to Next.js 16? Here is the root cause and adjustFontFallback fix with working code.
WordPress Performance: How I Cut Load Times by 60%
A step-by-step guide to optimizing WordPress performance. Caching, image optimization, CDN setup, and database cleanup that delivered 60% faster load times.
Core Web Vitals in 2026: The Complete Developer Guide
Everything developers need to know about Core Web Vitals in 2026. LCP, INP, CLS explained with real-world fixes and measurement strategies.
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