Performance
· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.Performance-focused optimization plan with CWV assessment, top offenders, and time estimates
First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.
1.48 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
6.88 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
29 ms
Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.
0.547
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
1.89 s
Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.
6.95 s
Page Load Progression
375 ms 750 ms
1.1 s
1.5 s
1.9 s 2.2 s 2.6 s 3.0 sFPage Weight BudgetAction17.9 MB transferred, 161 requestsFIX
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Image bandwidth is high — modern formats (WebP/AVIF) and resizing typically cut it 50%+.
Source: web.dev
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.
Source: web.dev
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
DPage Weight InventoryAction161 resources · 17.9 MB · 0 KB savings availableFIX
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 161 resources | 17.9 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
BImage Optimization32 images, 0 KB saveableREVIEW
Set explicit width and height to prevent CLS.
Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.
Source: web.dev / Core Web Vitals
BJS Execution Cost743ms total JS executionREVIEW
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://home.cern/ | 341ms | 2ms | 0ms | 3rd |
| Unattributable | 171ms | 3ms | 0ms | 3rd |
| https://home.cern/core/misc/drupal.init.js?v=10.4.5 | 89ms | 40ms | 0ms | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/prism/prism.js | 79ms | 73ms | 5ms | 3rd |
| https://home.cern/core/assets/vendor/jquery/jquery.min.js?v=3.7.1 | 63ms | 33ms | 4ms | 3rd |
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
A+Text CompressionAll text resources are compressedPASS
A+Font Loading6 fonts (149 KB)PASS
Web fonts
6
149 KB total
Render-blocking
0
of 6
Dominant font-display
swap
Most common across fonts
Font loading timeline
Optimization checklist
- Preload critical fonts (priority=high)
- Use woff2 format for all fonts
- Set font-display to swap, optional, or fallback
- Subset large fonts (≤100 KB each)
A+JS Bundles55 scripts, 0 KB unusedPASS
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://webanalytics.web.cern.ch/matomo.js | 22 KB | — | ✓ | 3rd |
| https://home.cern/core/assets/vendor/jquery/jquery.min.js?v=3.7.1 | 30 KB | — | ✓ | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/prism/prism.js | 95 KB | — | ✓ | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/colorbox/jquery.colorbox-min.js | 5 KB | — | ✓ | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/scroll-magic/ScrollMagic.min.js | 6 KB | — | ✓ | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/scroll-magic/text-effects.js | 2 KB | — | ✓ | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/owlcarousel/js/owl.carousel.js | 19 KB | — | ✗ | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/owlcarousel/js/owl.carousel2.thumbs.js | 2 KB | — | ✓ | 3rd |
| https://home.cern/core/assets/vendor/underscore/underscore-min.js?v=1.13.7 | 8 KB | — | ✓ | 3rd |
| https://home.cern/core/assets/vendor/once/once.min.js?v=1.0.1 | 1 KB | — | ✓ | 3rd |
A+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
Network Waterfall161 requests over 1640msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
home.cern home.cern | Other | 341ms | 18 KB | — | CHF5/mo | Costly |
Unattributable Unattributable | Other | 171ms | 0 KB | — | CHF3/mo | Optional |
home.cern home.cern | Other | 89ms | 1 KB | — | CHF1/mo | Optional |
framework.web.cern.ch framework.web.cern.ch | Other | 79ms | 95 KB | — | CHF1/mo | Optional |
home.cern home.cern | Other | 63ms | 30 KB | — | CHF1/mo | Optional |
These scripts may cost more than they're worth
- home.cern adds 341ms and costs ~CHF5/month
100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.
When third-party JS execution time exceeds your own, performance gains from frontend work are capped by code you don't own.
Learn more ▾ ▴
Every millisecond of third-party JS competes with your own for main-thread time. If their share is bigger than yours, optimization on your code base barely moves the needle. Audit, defer, or remove third-parties before further frontend optimization. Use Lighthouse's third-party audit to identify the worst offenders.
Source: web.dev
home.cern takes 341ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev