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.
3.92 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
84.96 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
400 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.
5.93 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.
85.84 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 BudgetAction16.5 MB transferred, 155 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
DJS Execution CostAction2003ms total JS executionFIX
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| Unattributable | 705ms | 13ms | 0ms | 3rd |
| https://home.cern/core/misc/drupal.init.js?v=10.4.5 | 354ms | 172ms | 0ms | 1st |
| https://framework.web.cern.ch/framework/3.0/js/prism/prism.js | 322ms | 293ms | 20ms | 3rd |
| https://home.cern/ | 211ms | 7ms | 1ms | 1st |
| https://framework.web.cern.ch/framework/3.0/js/scroll-magic/text-effects.js | 175ms | 28ms | 1ms | 3rd |
| https://home.cern/core/assets/vendor/jquery/jquery.min.js?v=3.7.1 | 166ms | 90ms | 7ms | 1st |
| https://webanalytics.web.cern.ch/matomo.js | 70ms | 43ms | 6ms | 3rd |
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
CPage Weight InventoryAction155 resources · 16.5 MB · 0 KB savings availableREVIEW
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 155 resources | 16.5 MiB | ||||||
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
A+Third-Party Impact5% third-party, 0 ms blockingPASS
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://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://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 | — | ✓ | 1st |
| 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 | — | ✓ | 1st |
| https://home.cern/core/assets/vendor/once/once.min.js?v=1.0.1 | 1 KB | — | ✓ | 1st |
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
A+HTTP Cachingmax-age=60 (1 minute)PASS
max-age=60, public
| Directive | Value | Meaning |
|---|---|---|
| max-age | 60 | Cache for 1 minute |
| public | — | Any cache may store this response |
Network Waterfall155 requests over 1429msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
Unattributable Unattributable | Other | 705ms | 0 KB | — | CHF11/mo | Costly |
framework.web.cern.ch framework.web.cern.ch | Other | 322ms | 95 KB | — | CHF5/mo | Costly |
framework.web.cern.ch framework.web.cern.ch | Other | 175ms | 2 KB | — | CHF3/mo | Optional |
webanalytics.web.cern.ch webanalytics.web.cern.ch | Other | 70ms | 22 KB | — | CHF1/mo | Optional |
These scripts may cost more than they're worth
- Unattributable adds 705ms and costs ~CHF11/month
- framework.web.cern.ch adds 322ms and costs ~CHF5/month
64% of JavaScript execution time comes from third-party scripts.
Third-party scripts (analytics, ads, social, A/B testing) often dominate execution time — every one is a perf-and-privacy tax.
Learn more ▾ ▴
Each third-party script is a black box: you don't control when it loads, what it executes, or how much it grows. They often account for a major share of total blocking time on average sites (HTTP Archive's Web Almanac documents the trend). Audit which ones you actually need, defer the rest, and use facade patterns (lite-youtube, lite-vimeo) for embedded media.
Source: web.dev / HTTP Archive Web Almanac
Unattributable takes 705ms 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 322ms 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