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https://uva.nl

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
74
GRADE
C
FIX
6
REVIEW
1
PASS
8
INFO
2

Performance-focused optimization plan with CWV assessment, top offenders, and time estimates

Mobile Desktop
46
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
96
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
100
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
100
SEO Measures basic SEO optimizations: meta tags, crawlability, link text, and mobile friendliness.

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

9.24 s

Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.

13.76 s

Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.

429 ms

Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.

0.000

Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.

9.24 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.

13.80 s

Page Load Progression

382 ms
765 ms
1.1 s
1.5 s
1.9 s
2.3 s
2.7 s
3.1 s
Checks
17
8 PASS 1 REVIEW 6 FIX
D
Page Weight Budget
Action
2.5 MB transferred, 40 requests
FIX
2.5 MB transferred, 40 requests
Warning::
Page weighs 3.8 MB (2.5 MB transferred)
Warning::
JavaScript is 1.0 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.0 MB
Info::
CSS is 372 KB — consider purging unused styles
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
Got: 372 KB
Info::
40 HTTP requests
Info::
Estimated 0.51 g CO2 per page load
2.5 MB / 2.4 MB budget
2.5 MB transferred
40 requests
0.51 g CO2 per page load
JavaScript 1.0 MiB 42%
Images 674.4 KiB 27%
CSS 372.4 KiB 15%
HTML 164.5 KiB 7%
Fonts 162.4 KiB 6%
Other 78.2 KiB 3%
Other 1.4 KiB 0%
Other 546 B 0%
Other 281 B 0%
0 2.4 MB 4.9 MB
Over budget

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Why this matters

JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.

Source: web.dev

Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.

Why this matters

CSS bundle is large — purge unused styles (PurgeCSS, Tailwind JIT) to reduce CSS payload.

Source: web.dev

D
Third-Party Impact
Action
100% third-party, 0 ms blocking
FIX
100% third-party, 0 ms blocking
Warning::
Third-party code accounts for 100% of page weight (2.5 MiB of 2.5 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Execution Cost
Action
2947ms total JS execution
FIX
2947ms total JS execution
Warning::
https://www.uva.nl/webfiles/1765960941537/js/app.j...: 1120ms CPU time
Warning::
https://www.uva.nl/: 375ms CPU time
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-HX9...: 368ms CPU time
Warning::
https://www.googletagmanager.com/gtag/js?id=G-44XG...: 345ms CPU time
Info::
Unattributable: 239ms CPU time
Warning::
Third-party scripts: 2947ms (100% of total)

Main Thread Breakdown

Script Evaluation 37% Style & Layout 21% Other 21% Rendering 10% Script Parsing & Compilation 7%
ScriptTotalScriptingParse/CompileParty
https://www.uva.nl/webfiles/1765960941537/js/app.js1120ms251ms30ms3rd
https://www.uva.nl/375ms16ms5ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-HX98368ms300ms63ms3rd
https://www.googletagmanager.com/gtag/js?id=G-44XGTNSN28&cx=c&gtm=4e64h1345ms254ms48ms3rd
Unattributable239ms13ms0ms3rd
https://siteimproveanalytics.com/js/siteanalyze_6004849.js179ms74ms35ms3rd
https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.4/config/TeX-AMS_HTML.js?V=2.7.4125ms96ms19ms3rd
https://www.uva.nl/webfiles/1765960941537/js/699.js124ms62ms10ms3rd
https://www.uva.nl/webfiles/1765960941537/js/365.js72ms13ms1ms3rd
F
JS Bundles
Action
12 scripts, 564 KB unused
FIX
12 scripts, 564 KB unused
Warning::
https://www.uva.nl/webfiles/1765960941537/js/app.j...: 194 KB unused (66%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.uva.nl/webfiles/1765960941537/js/699.j...: 102 KB unused (75%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://siteimproveanalytics.com/js/siteanalyze_60...: 69 KB unused (67%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=G-44XG...: 66 KB unused (39%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-HX9...: 66 KB unused (33%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 564 KB
564 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.uva.nl/webfiles/1765960941537/js/app.js295 KB194 KB (66%)✓3rd
https://www.uva.nl/webfiles/1765960941537/js/699.js137 KB102 KB (75%)✓3rd
https://siteimproveanalytics.com/js/siteanalyze_6004849.js104 KB69 KB (67%)✓3rd
https://www.googletagmanager.com/gtag/js?id=G-44XGTNSN28&cx=c&gtm=4e64h1170 KB66 KB (39%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-HX98198 KB66 KB (33%)✓3rd
https://analytics.ic.uva.nl/matomo.js67 KB38 KB (57%)✓3rd
https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.4/config/TeX-AMS_HTML.js?V=2.7.454 KB30 KB (57%)✓3rd
https://www.uva.nl/webfiles/1765960941537/js/uvacookiebar.js3 KB—✓3rd
https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.4/MathJax.js?config=TeX-AMS_HTML17 KB—✓3rd
https://www.uva.nl/webfiles/1765960941537/js/4.js7 KB—✓3rd

Consider code splitting or tree shaking to reduce unused code.

Why this matters

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.

Why this matters

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.

Why this matters

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.

Why this matters

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.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

F
Page Weight Inventory
Action
40 resources · 2.5 MB · 564 KB savings available
FIX
40 resources · 2.5 MB · 564 KB savings available
Warning::
Page weight 1.5 MB over 1MB target
Got: 2.5 MB Expected: ≤ 1 MB
Info::
~564 KB of savings available
Warning::
39 third-party resources (100% of weight)
Info::
3 resources over 200KB
40 resources · 2.5 MiB · 39 third-party 1.5 MiB over 1MB target
JavaScript 42% · 1.0 MiB
Image 30% · 751.9 KiB
CSS 15% · 372.4 KiB
Document 7% · 164.7 KiB
Font 6% · 162.4 KiB
Other 0% · 2.6 KiB

~564.4 KiB of savings available

Remove unused JavaScript: 564.4 KiB
F
HTTP Caching
Action
No cache headers
FIX
No cache headers
Warning::
No Cache-Control header found
Browsers will use heuristic caching, which can be unpredictable. Set explicit cache headers.

No Cache-Control header

Adding a Cache-Control header can significantly improve repeat-visit performance.

C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Text Compression
All text resources are compressed
PASS
All text resources are compressed
Info::
All text resources are compressed
All text resources are properly compressed.
A
Image Optimization
11 images, 0 KB saveable
PASS
11 images, 0 KB saveable
Info::
All images are well-optimized
11 images 674 KB
0 oversized -0 KB
3 legacy format
0 missing dimensions CLS risk
A+
Font Loading
4 fonts (162 KB)
PASS
4 fonts (162 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

162 KB total

Render-blocking

0

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s FCP 9.2 s LCP 13.8 shttps://use.typekit.net/af/4db8bf/00000000000000007735d61c/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/4db8bf/00000000000000007735d61c/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 43.1 KiB — 17 ms — font-display: swaphttps://use.typekit.net/af/14f0be/000000000000000077586386/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/14f0be/000000000000000077586386/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 37.7 KiB — 22 ms — font-display: swaphttps://use.typekit.net/af/642cd4/000000000000000077587094/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3l https://use.typekit.net/af/642cd4/000000000000000077587094/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3 — 38.0 KiB — 17 ms — font-display: swaphttps://use.typekit.net/af/4f35a4/00000000000000007735d633/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3l https://use.typekit.net/af/4f35a4/00000000000000007735d633/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3 — 43.7 KiB — 18 ms — font-display: swap
l woff2 swap
Size 43 KB
Load time 17 ms
Start 704 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 38 KB
Load time 22 ms
Start 705 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 38 KB
Load time 17 ms
Start 705 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 44 KB
Load time 18 ms
Start 705 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+
Resource Caching
All resources properly cached
PASS
All resources properly cached
Info::
No caching issues found
All static resources have appropriate caching headers.
A+
Critical Rendering Path
No render-blocking resources
PASS
No render-blocking resources
Info::
No render-blocking resources detected
A+
Resource Hints
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
A+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
Network Waterfall
40 requests over 1531ms
INFO
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s FCP 9.2 s LCP 13.8 shttps://uva.nl// https://uva.nl/ — 301 — 647 B — 115 ms — h2https://www.uva.nl/www.uva.nl/ https://www.uva.nl/ — 200 — 164.5 KiB — 264 ms — h2https://www.uva.nl/webfiles/1765960941537/css/app.min.csswww.uva.nl/webfiles/1765960941537/c... https://www.uva.nl/webfiles/1765960941537/css/app.min.css — 200 — 359.2 KiB — 124 ms — h2https://www.uva.nl/webfiles/1765960941537/js/uvacookiebar.jswww.uva.nl/webfiles/1765960941537/j... https://www.uva.nl/webfiles/1765960941537/js/uvacookiebar.js — 200 — 3.2 KiB — 95 ms — h2https://www.uva.nl/webfiles/1765960941537/includes/home-research-nl/home-research-nl.csswww.uva.nl/webfiles/1765960941537/i... https://www.uva.nl/webfiles/1765960941537/includes/home-research-nl/home-research-nl.css — 200 — 3.3 KiB — 95 ms — h2https://www.uva.nl/webfiles/1765960941537/includes/home-overdeuva-nl/home-overdeuva-nl.csswww.uva.nl/webfiles/1765960941537/i... https://www.uva.nl/webfiles/1765960941537/includes/home-overdeuva-nl/home-overdeuva-nl.css — 200 — 2.9 KiB — 94 ms — h2https://www.uva.nl/webfiles/1765960941537/_favicon/manifest.jsonwww.uva.nl/webfiles/1765960941537/_... https://www.uva.nl/webfiles/1765960941537/_favicon/manifest.json — 200 — 1.4 KiB — 119 ms — h2https://www.uva.nl/webfiles/1765960941537/js/app.jswww.uva.nl/webfiles/1765960941537/j... https://www.uva.nl/webfiles/1765960941537/js/app.js — 200 — 294.9 KiB — 74 ms — h2https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.4/MathJax.js?config=TeX-AMS_HTMLcdnjs.cloudflare.com/ajax/libs/math... https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.4/MathJax.js?config=TeX-AMS_HTML — 200 — 17.3 KiB — 103 ms — h3https://use.typekit.net/emf5eij.cssuse.typekit.net/emf5eij.css https://use.typekit.net/emf5eij.css — 200 — 1.2 KiB — 56 ms — h2https://www.googletagmanager.com/gtm.js?id=GTM-HX98www.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-HX98 — 200 — 197.7 KiB — 194 ms — h2https://www.uva.nl/webfiles/1765960941537/css/print.min.csswww.uva.nl/webfiles/1765960941537/c... https://www.uva.nl/webfiles/1765960941537/css/print.min.css — 200 — 5.8 KiB — 40 ms — h2https://p.typekit.net/p.css?s=1&k=emf5eij&ht=tk&f=13378.13379.13380.13381.13382.13383.17265.17270.17272&a=13802896&app=typekit&e=cssp.typekit.net/p.css?s=1&k=emf5eij&h... https://p.typekit.net/p.css?s=1&k=emf5eij&ht=tk&f=13378.13379.13380.13381.13382.13383.17265.17270.17272&a=13802896&app=typekit&e=css — 200 — 172 B — 68 ms — h2https://analytics.ic.uva.nl/matomo.jsanalytics.ic.uva.nl/matomo.js https://analytics.ic.uva.nl/matomo.js — 200 — 66.7 KiB — 303 ms — http/1.1https://www.uva.nl/webfiles/1765960941537/icons/svg-logos.svgwww.uva.nl/webfiles/1765960941537/i... https://www.uva.nl/webfiles/1765960941537/icons/svg-logos.svg — 200 — 69.6 KiB — 40 ms — h2data:image/svg+xml;charset=utf8, %3Csvg height='20' viewBox='0 0 20 20' width='20' xmlns='http://ww…ww… data:image/svg+xml;charset=utf8, %3Csvg height='20' viewBox='0 0 20 20' width='20' xmlns='http://ww… — 200 — 0 B — 0 ms — datadata:image/svg+xml;charset=utf8, %3Csvg xmlns='http://www.w3.org/2000/svg' height='100' viewBox='0 …www.w3.org/2000/svg' height='100' v... data:image/svg+xml;charset=utf8, %3Csvg xmlns='http://www.w3.org/2000/svg' height='100' viewBox='0 … — 200 — 0 B — 0 ms — datahttps://www.uva.nl/webfiles/1765960941537/js/4.jswww.uva.nl/webfiles/1765960941537/j... https://www.uva.nl/webfiles/1765960941537/js/4.js — 200 — 7.2 KiB — 40 ms — h2https://www.uva.nl/webfiles/1765960941537/js/365.jswww.uva.nl/webfiles/1765960941537/j... https://www.uva.nl/webfiles/1765960941537/js/365.js — 200 — 3.8 KiB — 40 ms — h2https://www.uva.nl/webfiles/1765960941537/js/812.jswww.uva.nl/webfiles/1765960941537/j... https://www.uva.nl/webfiles/1765960941537/js/812.js — 200 — 2.4 KiB — 40 ms — h2https://use.typekit.net/af/4db8bf/00000000000000007735d61c/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3use.typekit.net/af/4db8bf/000000000... https://use.typekit.net/af/4db8bf/00000000000000007735d61c/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 200 — 43.1 KiB — 17 ms — h2https://use.typekit.net/af/14f0be/000000000000000077586386/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3use.typekit.net/af/14f0be/000000000... https://use.typekit.net/af/14f0be/000000000000000077586386/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 200 — 37.7 KiB — 22 ms — h2https://use.typekit.net/af/642cd4/000000000000000077587094/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3use.typekit.net/af/642cd4/000000000... https://use.typekit.net/af/642cd4/000000000000000077587094/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3 — 200 — 38.0 KiB — 17 ms — h2https://use.typekit.net/af/4f35a4/00000000000000007735d633/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3use.typekit.net/af/4f35a4/000000000... https://use.typekit.net/af/4f35a4/00000000000000007735d633/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3 — 200 — 43.7 KiB — 18 ms — h2https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.4/config/TeX-AMS_HTML.js?V=2.7.4cdnjs.cloudflare.com/ajax/libs/math... https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.4/config/TeX-AMS_HTML.js?V=2.7.4 — 200 — 53.7 KiB — 48 ms — h3https://www.googletagmanager.com/gtag/js?id=G-44XGTNSN28&cx=c&gtm=4e64h1www.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-44XGTNSN28&cx=c&gtm=4e64h1 — 200 — 169.8 KiB — 42 ms — h2https://siteimproveanalytics.com/js/siteanalyze_6004849.jssiteimproveanalytics.com/js/siteana... https://siteimproveanalytics.com/js/siteanalyze_6004849.js — 200 — 103.9 KiB — 144 ms — h3https://www.uva.nl/webfiles/1765960941537/js/699.jswww.uva.nl/webfiles/1765960941537/j... https://www.uva.nl/webfiles/1765960941537/js/699.js — 200 — 136.9 KiB — 41 ms — h2https://www.uva.nl/binaries/_ht_1744634291896/480x700-webp/content/gallery/evenementen/2025/minorweek/202504-kies-je-minor.pngwww.uva.nl/binaries/_ht_17446342918... https://www.uva.nl/binaries/_ht_1744634291896/480x700-webp/content/gallery/evenementen/2025/minorweek/202504-kies-je-minor.png — 200 — 20.7 KiB — 38 ms — h2https://www.uva.nl/binaries/_ht_1775637956190/480x700-webp/content/gallery/faculteiten-en-diensten/uva-bureau-communicatie/persvoorlichting/2026/pexels-gabby-k-5841764.jpgwww.uva.nl/binaries/_ht_17756379561... 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0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s FCP 9.2 s LCP 13.8 shttps://uva.nl// https://uva.nl/ — 301 — 647 B — 115 ms — h2https://www.uva.nl/www.uva.nl/ https://www.uva.nl/ — 200 — 164.5 KiB — 264 ms — h2https://www.uva.nl/webfiles/1765960941537/css/app.min.csswww.uva.nl/webfiles/1765960941537/c... https://www.uva.nl/webfiles/1765960941537/css/app.min.css — 200 — 359.2 KiB — 124 ms — h2https://www.uva.nl/webfiles/1765960941537/js/uvacookiebar.jswww.uva.nl/webfiles/1765960941537/j... https://www.uva.nl/webfiles/1765960941537/js/uvacookiebar.js — 200 — 3.2 KiB — 95 ms — h2https://www.uva.nl/webfiles/1765960941537/includes/home-research-nl/home-research-nl.csswww.uva.nl/webfiles/1765960941537/i... https://www.uva.nl/webfiles/1765960941537/includes/home-research-nl/home-research-nl.css — 200 — 3.3 KiB — 95 ms — h2https://www.uva.nl/webfiles/1765960941537/includes/home-overdeuva-nl/home-overdeuva-nl.csswww.uva.nl/webfiles/1765960941537/i... 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HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
100% of JavaScript execution is third-party
First-party Third-party 2947ms · 1125KB · €32/mo
www.uva.nl
Other
Costly
Execution 1120ms
Transfer 295 KB
Unused 66%
Monthly Cost €12/mo
www.uva.nl
Other
Costly
Execution 375ms
Transfer 164 KB
Monthly Cost €4/mo
Google Tag Manager
Tag Manager
Costly
Execution 368ms
Transfer 198 KB
Unused 33%
Monthly Cost €4/mo
Google Tag Manager
Tag Manager
Costly
Execution 345ms
Transfer 170 KB
Unused 39%
Monthly Cost €4/mo
Unattributable
Other
Costly
Execution 239ms
Transfer 0 KB
Monthly Cost €3/mo
siteimproveanalytics.com
Other
Optional
Execution 179ms
Transfer 104 KB
Unused 67%
Monthly Cost €2/mo
cdnjs
CDN
Optional
Execution 125ms
Transfer 54 KB
Unused 57%
Monthly Cost €1/mo
www.uva.nl
Other
Optional
Execution 124ms
Transfer 137 KB
Unused 75%
Monthly Cost €1/mo
www.uva.nl
Other
Optional
Execution 72ms
Transfer 4 KB
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • www.uva.nl adds 1120ms and costs ~€12/month
  • www.uva.nl adds 375ms and costs ~€4/month
  • Google Tag Manager adds 368ms and costs ~€4/month
  • Google Tag Manager adds 345ms and costs ~€4/month
  • Unattributable adds 239ms and costs ~€3/month

100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.

Why this matters

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

www.uva.nl takes 1120ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

66% of www.uva.nl's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

Source: web.dev

www.uva.nl takes 375ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

Google Tag Manager takes 368ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

Google Tag Manager takes 345ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

Unattributable takes 239ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

67% of siteimproveanalytics.com's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

Source: web.dev

57% of cdnjs's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

Source: web.dev

75% of www.uva.nl's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

Source: web.dev

How third-party costs are calculated

All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.

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