Browser & Rendering Speed Intelligence
How Fast Does Your Device Render?
Live Core Web Vitals plus JS, DOM, canvas, and memory benchmarks — measured the moment this page loads.
Understanding Every Signal
What each Web Vital and benchmark score actually measures.
Core Web Vitals
Largest Contentful Paint (LCP) & Rating
LCP measures how long until the largest visible element — typically a hero image or the main heading — finishes rendering. Under 2.5s is Good; 2.5–4s Needs Improvement; above 4s Poor. It's Google's primary measure of perceived loading speed and is used as a search ranking signal.
First Contentful Paint (FCP) & Rating
FCP is when the browser first renders any content at all — text, an image, or a background. It's the moment the page stops feeling blank. Under 1.8s is Good. FCP can be significantly faster than LCP if small text renders before a large image finishes loading.
Cumulative Layout Shift (CLS) & Rating
CLS measures unexpected visual movement — elements shifting position after they've appeared, causing accidental taps and disorienting reads. Under 0.1 is Good; above 0.25 is Poor. Common causes include images without declared dimensions and content injected above existing content after the initial render.
Interaction to Next Paint (INP) & Rating
INP replaced First Input Delay as a Core Web Vital in March 2024. Where FID only measured the first interaction, INP measures the worst-case responsiveness across all interactions during a session. Under 200ms is Good. High INP usually indicates heavy JavaScript blocking the main thread.
TTFB Rating & First Input Delay (FID)
TTFB and FID ratings contextualise the raw values from the Performance panel. FID is the legacy predecessor to INP — still useful for understanding first-interaction responsiveness on devices where INP hasn't yet been observed.
Device Benchmarks
JS Execution Score & Time
A fixed computational workload — sorting, arithmetic, string manipulation — timed in milliseconds. The score normalises this against expected performance for this device class. It reflects raw CPU and JS engine speed, entirely independent of network conditions.
DOM Manipulation Score & Time
Times a fixed sequence of DOM operations — creating nodes, modifying attributes, measuring layout. Slow DOM manipulation is often what makes pages feel sluggish in interaction even when they load quickly.
Canvas Render Score & Time
Times a series of 2D canvas drawing operations. This benchmark reflects the combined speed of your CPU and GPU for 2D graphics — relevant for canvas-heavy applications, data visualisation, and image editing tools.
Memory Access Score & Time
Times large array allocation and traversal to measure memory bandwidth and cache efficiency. Low scores here often indicate constrained memory on low-end devices where even well-written code hits performance ceilings.
CSS Animation Score & FPS
Measures frames per second during a CSS animation workload. 60 FPS is the target for smooth animation on most displays; 90+ FPS is ideal on high-refresh-rate screens. Values below 30 FPS produce visibly janky animation.
Event Loop Score & Average, Overall Benchmark & Percentile Rankings
Event loop average measures how long tasks wait before executing — high values indicate a blocked main thread. The overall benchmark combines all scores into a single number. Percentile rankings contextualise that number against typical values for average mobile and desktop devices, and against top-tier devices, giving a relative position rather than just an absolute score.
Why Core Web Vitals Are Now a Search Ranking Signal
Google made user experience measurable and consequential
Before Core Web Vitals, page speed was measured by technical metrics that didn't always correlate with actual user experience. LCP, CLS, and INP were chosen specifically because field data showed they predict whether users bounce from pages. Google's 2021 Page Experience update made them ranking signals, which created a direct financial incentive for site owners to optimise for real user experience rather than synthetic test scores.