https://home.cern
Performance
· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.SCORE
82
GRADE
B
FIX
1
REVIEW
4
PASS
8
INFO
2
Performance-focused optimization plan with CWV assessment, top offenders, and time estimates
51
80
96
100
First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.
814 ms
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
14.82 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
51 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.
1.40 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.
14.88 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 sChecks
158 PASS 4 REVIEW 1 FIX
FPage Weight BudgetAction16.6 MB transferred, 160 requestsFIX
Page Weight Budget
Action16.6 MB transferred, 160 requests
16.6 MB transferred, 160 requests
Critical::
Page weighs 17.7 MB (16.6 MB transferred)
Warning::
Images are 16.0 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 16.0 MB
Warning::
160 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 3.5 g CO2 per page load
16.6 MB transferred
160 requests
3.5 g CO2 per page load
Images 16.0 MiB 97%
JavaScript 285.2 KiB 2%
Fonts 148.7 KiB 1%
CSS 116.5 KiB 1%
HTML 18.4 KiB 0%
Other 5.6 KiB 0%
Other 370 B 0%
0 2.4 MB 4.9 MB
Over budget
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Why this matters
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.
Why this matters
High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.
Source: web.dev
BImage Optimization32 images, 0 KB saveableREVIEW
Image Optimization
32 images, 0 KB saveable
32 images, 0 KB saveable
Warning::
https://home.cern/sites/default/files/logo/cern-lo... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
32 images 16.0 MB
0 oversized -0 KB
32 legacy format
1 missing dimensions CLS risk
Set explicit width and height to prevent CLS.
Why this matters
Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.
Source: web.dev / Core Web Vitals
BJS Execution Cost798ms total JS executionREVIEW
JS Execution Cost
798ms total JS execution
798ms total JS execution
Warning::
https://home.cern/: 347ms CPU time
Info::
Unattributable: 177ms CPU time
Info::
https://home.cern/core/misc/drupal.init.js?v=10.4....: 116ms CPU time
Info::
https://framework.web.cern.ch/framework/3.0/js/pri...: 99ms CPU time
Info::
https://home.cern/core/assets/vendor/jquery/jquery...: 60ms CPU time
Info::
Third-party scripts: 276ms (35% of total)
Main Thread Breakdown
Other 39% Script Evaluation 25% Style & Layout 20% Rendering 11%
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://home.cern/ | 347ms | 2ms | 0ms | 1st |
| Unattributable | 177ms | 3ms | 0ms | 3rd |
| https://home.cern/core/misc/drupal.init.js?v=10.4.5 | 116ms | 51ms | 0ms | 1st |
| https://framework.web.cern.ch/framework/3.0/js/prism/prism.js | 99ms | 91ms | 6ms | 3rd |
| https://home.cern/core/assets/vendor/jquery/jquery.min.js?v=3.7.1 | 60ms | 42ms | 2ms | 1st |
CPage Weight InventoryAction160 resources · 16.6 MB · 0 KB savings availableREVIEW
Page Weight Inventory
Action160 resources · 16.6 MB · 0 KB savings available
160 resources · 16.6 MB · 0 KB savings available
Warning::
Page weight 15.6 MB over 1MB target
Got: 16.6 MB Expected: ≤ 1 MB
Info::
19 third-party resources (5% of weight)
Info::
11 resources over 200KB
160 resources · 16.6 MiB · 19 third-party 15.6 MiB over 1MB target
Image 97% · 16.0 MiB
JavaScript 2% · 285.2 KiB
Font 1% · 148.7 KiB
CSS 1% · 116.5 KiB
Document 0% · 18.4 KiB
Other 0% · 370 B
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 160 resources | 16.6 MiB | ||||||
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
ActionWhether the site is served from green-energy infrastructure
Green Hosting
No green hosting detected
A+Third-Party Impact5% third-party, 0 ms blockingPASS
Third-Party Impact
5% third-party, 0 ms blocking
5% third-party, 0 ms blocking
Info::
Third-party code accounts for 5% of page weight (819.1 KiB of 16.6 MiB)
Info::
Third-party blocking time is low (0 ms)
95%
First-party Third-party
A+Text CompressionAll text resources are compressedPASS
Text Compression
All text resources are compressed
All text resources are compressed
Info::
All text resources are compressed
All text resources are properly compressed.
A+Font Loading6 fonts (149 KB)PASS
Font Loading
6 fonts (149 KB)
6 fonts (149 KB)
Info::
6 font(s) use font-display: swap (FOUT risk but functional)
Web fonts
6
149 KB total
Render-blocking
0
of 6
Dominant font-display
swap
Most common across fonts
Font loading timeline
Transfer FOIT (block) FOUT (swap)
regular.woff2 woff2 swap
Size 27 KB
Load time 141 ms
Start 655 ms
Risk FOUT — text flashes from fallback to web font
bold.woff2 woff2 swap
Size 19 KB
Load time 132 ms
Start 655 ms
Risk FOUT — text flashes from fallback to web font
cern.woff2 woff2 swap
Size 21 KB
Load time 132 ms
Start 655 ms
Risk FOUT — text flashes from fallback to web font
semibold.woff2 woff2 swap
Size 27 KB
Load time 135 ms
Start 656 ms
Risk FOUT — text flashes from fallback to web font
light.woff2 woff2 swap
Size 27 KB
Load time 142 ms
Start 656 ms
Risk FOUT — text flashes from fallback to web font
bold.woff2 woff2 swap
Size 27 KB
Load time 140 ms
Start 656 ms
Risk FOUT — text flashes from fallback to web font
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
JS Bundles
55 scripts, 0 KB unused
55 scripts, 0 KB unused
0 KB unused JavaScript
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
Resource Caching
All resources properly cached
All resources properly cached
Info::
No caching issues found
All static resources have appropriate caching headers.
A+Critical Rendering PathNo render-blocking resourcesPASS
Critical Rendering Path
No render-blocking resources
No render-blocking resources
Info::
No render-blocking resources detected
A+Resource HintsNo optimization neededPASS
Resource Hints
No optimization needed
No optimization needed
Info::
No resource hint issues
A+HTTP Cachingmax-age=60 (1 minute)PASS
HTTP Caching
max-age=60 (1 minute)
max-age=60 (1 minute)
Info::
Cache-Control header is set
Got: max-age=60, public
Info::
Effective TTL: 1 minute (max-age=60)
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present
Cache-Control
max-age=60, public
| Directive | Value | Meaning |
|---|---|---|
| max-age | 60 | Cache for 1 minute |
| public | — | Any cache may store this response |
Effective TTL: 60 seconds
Network Waterfall160 requests over 1548msINFO
Network Waterfall
160 requests over 1548ms
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
35% of JavaScript execution is third-party
First-party Third-party 276ms · 95KB · CHF4/mo
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
Unattributable Unattributable | Other | 177ms | 0 KB | — | CHF3/mo | Optional |
framework.web.cern.ch framework.web.cern.ch | Other | 99ms | 95 KB | — | CHF2/mo | Optional |
Unattributable
Other
Execution 177ms
Transfer 0 KB
Monthly Cost CHF3/mo
framework.web.cern.ch
Other
Execution 99ms
Transfer 95 KB
Monthly Cost CHF2/mo
All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.