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.
1.12 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
2.97 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
83 ms
Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.
0.002
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
2.01 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.
2.98 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 sDThird-Party ImpactAction100% third-party, 0 ms blockingFIX
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
BPage Weight Budget1.2 MB transferred, 35 requestsREVIEW
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.
Source: web.dev
Subset fonts to include only used characters, or switch to system font stacks.
Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).
Source: web.dev font loading
BImage Optimization10 images, 0 KB saveableREVIEW
CJS BundlesAction9 scripts, 224 KB unusedREVIEW
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.googletagmanager.com/gtag/js?id=G-WJ30DT8NHH&cx=c>m=4e64h1h1 | 174 KB | 67 KB (38%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-KLP5L3 | 140 KB | 60 KB (43%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-1011997553&cx=c>m=4e64h1h1 | 137 KB | 55 KB (40%) | ✓ | 3rd |
| https://www.uu.nl/sites/default/files/js/js_fIuyj-NbX6po2XB1dHXpIZBmMzDPeGSiLEGshDOy22w.js?scope=footer&delta=0&language=nl&theme=corp&include=eJwtzUEOwjAMRNELYXIk5CQmtXDt4DhI5fRUpMs3fzHojI8y3Ukj4Qm4AIofbhhsCsL6GoBqeuw2x62YU6o-O8q9mAj2QWvcrZIrf30xMGfM8o890XuiwEbctoCCXuFpFuRj5SaWzz7iOP_aD_JqO1M | 48 KB | 22 KB (46%) | ✓ | 3rd |
| https://code.jquery.com/jquery-3.7.0.min.js | 30 KB | 20 KB (69%) | ✓ | 3rd |
| https://www.uu.nl/core/assets/vendor/modernizr/modernizr.min.js?v=3.11.7 | 3 KB | — | ✓ | 3rd |
| https://analytics.ahrefs.com/analytics.js | 3 KB | — | ✓ | 3rd |
| https://googleads.g.doubleclick.net/pagead/viewthroughconversion/1011997553/?random=1776803480399&cv=11&fst=1776803480399&bg=ffffff&guid=ON&async=1&en=gtag.config>m=45be64h1h1v9186583567z871462251za20gzb71462251zd71462251xec&gcd=13l3l3l3l1l1&dma=0&tag_exp=0~115938466~115938468~117266401~117384405&u_w=800&u_h=600&url=https%3A%2F%2Fwww.uu.nl%2F&rcb=3&frm=0&tiba=Universiteit%20Utrecht%20%7C%20Sharing%20science%2C%20shaping%20tomorrow&hn=www.googleadservices.com&npa=0&pscdl=noapi&auid=1895819764.1776803480&uaa=x86&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uamb=0&uam=&uap=macOS&uapv=10.15.7&uaw=0&data=event%3Dgtag.config&rfmt=3&fmt=4 | 2 KB | — | ✓ | 3rd |
| https://googleads.g.doubleclick.net/pagead/viewthroughconversion/1010142274/?random=1776803480431&cv=11&fst=1776803480431&bg=ffffff&guid=ON&async=1&en=gtag.config>m=45be64h1h1v9186583567z871462251za20gzb71462251zd71462251xec&gcd=13l3l3l3l1l1&dma=0&tag_exp=0~115938466~115938468~117266401~117384405&u_w=800&u_h=600&url=https%3A%2F%2Fwww.uu.nl%2F&rcb=3&frm=0&tiba=Universiteit%20Utrecht%20%7C%20Sharing%20science%2C%20shaping%20tomorrow&hn=www.googleadservices.com&npa=0&pscdl=noapi&auid=1895819764.1776803480&uaa=x86&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uamb=0&uam=&uap=macOS&uapv=10.15.7&uaw=0&data=event%3Dgtag.config&rfmt=3&fmt=4 | 2 KB | — | ✓ | 3rd |
Consider code splitting or tree shaking to reduce unused code.
This bundle has high unused code — code-split or tree-shake to ship only what executes.
Source: web.dev / Lighthouse coverage
Consider code splitting or tree shaking to reduce unused code.
This bundle has high unused code — code-split or tree-shake to ship only what executes.
Source: web.dev / Lighthouse coverage
Consider code splitting or tree shaking to reduce unused code.
This bundle has high unused code — code-split or tree-shake to ship only what executes.
Source: web.dev / Lighthouse coverage
Consider code splitting or tree shaking to reduce unused code.
This bundle has high unused code — code-split or tree-shake to ship only what executes.
Source: web.dev / Lighthouse coverage
Consider code splitting or tree shaking to reduce unused code.
This bundle has high unused code — code-split or tree-shake to ship only what executes.
Source: web.dev / Lighthouse coverage
CPage Weight InventoryAction35 resources · 1.2 MB · 224 KB savings availableREVIEW
~223.7 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 35 resources | 1.2 MiB | ||||||
A+Text CompressionAll text resources are compressedPASS
A+JS Execution Cost473ms total JS executionPASS
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.googletagmanager.com/gtm.js?id=GTM-KLP5L3 | 134ms | 113ms | 16ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=G-WJ30DT8NHH&cx=c>m=4e64h1h1 | 99ms | 79ms | 19ms | 3rd |
| https://www.uu.nl/ | 92ms | 5ms | 1ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-1011997553&cx=c>m=4e64h1h1 | 89ms | 74ms | 13ms | 3rd |
| Unattributable | 59ms | 3ms | 0ms | 3rd |
A+Font Loading5 fonts (299 KB)PASS
Web fonts
5
299 KB total
Render-blocking
0
of 5
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+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
A+Green HostingWhether the site is served from green-energy infrastructurePASS
Green Hosting
This site is hosted on green energy infrastructure
Provider: Combell
Network Waterfall35 requests over 2144msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
Google Tag Manager www.googletagmanager.com | Tag Manager | 134ms | 140 KB | 43% | €1/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 99ms | 174 KB | 38% | €1/mo | Optional |
www.uu.nl www.uu.nl | Other | 92ms | 8 KB | — | €1/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 89ms | 137 KB | 40% | €1/mo | Optional |
Unattributable Unattributable | Other | 59ms | 0 KB | — | €1/mo | Optional |
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