Performance
· 17 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.
6.18 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
92.77 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
457 ms
Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.
0.013
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
6.59 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.
93.60 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 BudgetAction17.8 MB transferred, 156 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
DJS Execution CostAction2141ms total JS executionFIX
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| Unattributable | 776ms | 13ms | 0ms | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/prism/prism.js | 385ms | 357ms | 22ms | 3rd |
| https://home.cern/core/misc/drupal.init.js?v=10.4.5 | 338ms | 171ms | 1ms | 3rd |
| https://home.cern/ | 227ms | 9ms | 1ms | 3rd |
| https://framework.web.cern.ch/framework/3.0/js/scroll-magic/text-effects.js | 193ms | 28ms | 1ms | 3rd |
| https://home.cern/core/assets/vendor/jquery/jquery.min.js?v=3.7.1 | 151ms | 86ms | 6ms | 3rd |
| https://webanalytics.web.cern.ch/matomo.js | 73ms | 41ms | 6ms | 3rd |
DPage Weight InventoryAction156 resources · 17.8 MB · 0 KB savings availableFIX
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 156 resources | 17.8 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
BImage Optimization27 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
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 Hints1 hints, 0 missing preconnectsPASS
Current Resource Hints
1 resource hints configured
A+Render-Blocking ResourcesNo render-blocking resources detectedPASS
A+Third-Party ResourcesNo third-party resources detectedPASS
Network Waterfall156 requests over 1607msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
Unattributable Unattributable | Other | 776ms | 0 KB | — | CHF12/mo | Costly |
framework.web.cern.ch framework.web.cern.ch | Other | 385ms | 95 KB | — | CHF6/mo | Costly |
home.cern home.cern | Other | 338ms | 1 KB | — | CHF5/mo | Costly |
home.cern home.cern | Other | 227ms | 18 KB | — | CHF4/mo | Costly |
framework.web.cern.ch framework.web.cern.ch | Other | 193ms | 2 KB | — | CHF3/mo | Optional |
home.cern home.cern | Other | 151ms | 30 KB | — | CHF2/mo | Optional |
webanalytics.web.cern.ch webanalytics.web.cern.ch | Other | 73ms | 22 KB | — | CHF1/mo | Optional |
These scripts may cost more than they're worth
- Unattributable adds 776ms and costs ~CHF12/month
- framework.web.cern.ch adds 385ms and costs ~CHF6/month
- home.cern adds 338ms and costs ~CHF5/month
- home.cern adds 227ms and costs ~CHF4/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
Unattributable takes 776ms 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
framework.web.cern.ch takes 385ms 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
home.cern takes 338ms 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
home.cern takes 227ms 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