Documentation for PerfReviews Insights and Simple mode tests.
This section explains how the product works and what each automated test is trying to tell you. It follows the same spirit as WebPerf Snippets documentation, but translated into the user-facing workflow of PerfReviews Insights.
PerfReviews Insights is actively evolving.
We publish a simplified roadmap here to show what is already live, what we are actively moving toward next, and which deeper diagnostics are planned for later. It is intended as a product signal, not as a fixed release schedule.
- •CLS to catch unstable layouts during load
- •Render-blocking resources to explain blank-screen delays
- •Above-the-fold lazy image detection for LCP-heavy pages
- •Expanded Simple mode catalog with visible loading and media checks
- •FCP to complete the early-loading picture alongside TTFB and LCP
- •Priority Hints Audit for critical-image and critical-resource ordering
- •Resource Hints Validation to surface preload, preconnect, and prefetch gaps
- •INP and interaction debugging for responsiveness issues
- •Long tasks and long animation frames for main-thread bottlenecks
- •Advanced diagnostics such as critical CSS, hydration payloads, and bfcache readiness
Simple mode test catalog
Simple mode currently runs nine automated checks. Each page below explains what the test measures, why it matters, what you learn from the result, and which fixes are commonly relevant.
A page that jumps around feels broken even when it loads quickly. CLS is a Core Web Vital and is often harmed by images without dimensions, injected UI, unstable embeds, or late-loading fonts.
Read test guideTTFB, FCP, and LCP form a sequential chain — each one cannot be faster than the previous. Measuring them together in one load makes the numbers comparable and reveals where in that chain the slowdown actually sits.
Read test guideEven when the server responds quickly, render-blocking files can delay the moment users see anything useful. This directly hurts FCP and often LCP too.
Read test guideLazy loading is useful below the fold, but it is harmful when applied to hero images or other visible content. This usually delays LCP and makes the page feel slower than it should.
Read test guideImages are often the heaviest resource type on a page and they frequently decide whether the page feels fast or sluggish. A badly loaded hero image can hurt LCP, while missing dimensions can trigger layout shifts.
Read test guideVideo is one of the easiest ways to accidentally overload a page. Poor preload behavior, missing posters, or heavy media files can delay visible content and waste bandwidth before the user interacts.
Read test guideHeavy pages are slower to download, parse, and render, especially on mobile networks. Page weight often reveals whether JavaScript bundles, images, fonts, or third-party requests are dominating the experience.
Read test guideThird-party scripts are code you do not control, but they still compete for bandwidth, execution time, and CPU. A single badly loaded script can delay rendering or interaction for the entire page.
Read test guide