Skip to content
https://rug.nl

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
73
GRADE
C
FIX
5
REVIEW
2
PASS
6
INFO
2

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

Mobile Desktop
68
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
94
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.

997 ms

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

2.53 s

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

15 ms

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

0.331

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

1.16 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.

3.46 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 s
Checks
15
6 PASS 2 REVIEW 5 FIX
F
Page Weight Budget
Action
5.2 MB transferred, 51 requests
FIX
5.2 MB transferred, 51 requests
Critical::
Page weighs 6.9 MB (5.2 MB transferred)
Warning::
Images are 4.3 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 4.3 MB
Warning::
JavaScript is 656 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 656 KB
Info::
51 HTTP requests
Info::
Estimated 1.1 g CO2 per page load
5.2 MB / 2.4 MB budget
5.2 MB transferred
51 requests
1.1 g CO2 per page load
Images 4.3 MiB 83%
JavaScript 656.3 KiB 12%
Fonts 197.1 KiB 4%
CSS 48.5 KiB 1%
HTML 9.3 KiB 0%
Other 7.4 KiB 0%
Other 567 B 0%
Other 449 B 0%
Other 0 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

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

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 (5.2 MiB of 5.2 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Bundles
Action
20 scripts, 281 KB unused
FIX
20 scripts, 281 KB unused
Warning::
https://www.googletagmanager.com/gtag/js?id=G-0JTJ...: 68 KB unused (38%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-WLH...: 67 KB unused (42%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.rug.nl/_definition/shared/js/jquery-ui...: 57 KB unused (90%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://rug.containers.piwik.pro/d759d682-1760-4f6...: 39 KB unused (55%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.rug.nl/_definition/shared/js/interface...: 27 KB unused (70%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.rug.nl/_definition/shared/js/interface...: unminified — 10 KB could be saved
Info::
Total unused JavaScript: 281 KB
281 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtag/js?id=G-0JTJS4VF7S&cx=c&gtm=4e64k0h2179 KB68 KB (38%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-WLHD85V159 KB67 KB (42%)✓3rd
https://www.rug.nl/_definition/shared/js/jquery-ui.js?version=2026-03-1265 KB57 KB (90%)✓3rd
https://rug.containers.piwik.pro/d759d682-1760-4f61-8228-ee5bb7baedc3.js71 KB39 KB (55%)✓3rd
https://www.rug.nl/_definition/shared/js/interface.bundle.js?version=2026-03-1239 KB27 KB (70%)✗3rd
https://www.rug.nl/_definition/shared/js/fotorama.js?version=2026-03-1228 KB23 KB (84%)✗3rd
https://www.rug.nl/_definition/shared/js/cross-frame.js?version=2026-03-121 KB—✓3rd
https://www.rug.nl/_definition/shared/js/ucms.js?version=2026-03-1214 KB—✓3rd
https://www.rug.nl/_definition/shared/js/imagesloaded.js?version=2026-03-122 KB—✓3rd
https://www.rug.nl/_definition/shared/js/jquery.mobile.custom.min.js?version=2026-03-124 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

D
Page Weight Inventory
Action
51 resources · 5.2 MB · 281 KB savings available
FIX
51 resources · 5.2 MB · 281 KB savings available
Warning::
Page weight 4.2 MB over 1MB target
Got: 5.2 MB Expected: ≤ 1 MB
Info::
~281 KB of savings available
Warning::
50 third-party resources (100% of weight)
Info::
7 resources over 200KB
51 resources · 5.2 MiB · 50 third-party 4.2 MiB over 1MB target
Image 83% · 4.3 MiB
JavaScript 12% · 656.3 KiB
Font 4% · 197.1 KiB
CSS 1% · 48.5 KiB
Document 0% · 9.3 KiB
Other 0% · 1.2 KiB

~281.3 KiB of savings available

Remove unused JavaScript: 281.3 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
Image Optimization
Action
17 images, 0 KB saveable
REVIEW
17 images, 0 KB saveable
Warning::
https://www.rug.nl/about-ug/latest-news/news/archi... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/infonet/medewerkers/actueel/new... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/fse/news/technology/1024-opensc... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/magazine/0421-lehmannhome1mediu... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/images/homepage/cards/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/images/homepage/cards/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/policy-and-strategy/re... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/images/homepage/cards/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/latest-news/news/dossi... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/latest-news/news/archi... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/images/homepage/items/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/about-ug/latest-news/news/archi... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.rug.nl/_definition/shared/images/logo-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
17 images 4.3 MB
0 oversized -0 KB
17 legacy format
13 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

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

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

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

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

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

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

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

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

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

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

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

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

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+
JS Execution Cost
347ms total JS execution
PASS
347ms total JS execution
Info::
https://www.rug.nl/: 101ms CPU time
Info::
Unattributable: 97ms CPU time
Info::
https://www.googletagmanager.com/gtag/js?id=G-0JTJ...: 83ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-WLH...: 66ms CPU time
Warning::
Third-party scripts: 347ms (100% of total)

Main Thread Breakdown

Script Evaluation 46% Other 22% Style & Layout 14% Script Parsing & Compilation 10% Rendering 5%
ScriptTotalScriptingParse/CompileParty
https://www.rug.nl/101ms1ms0ms3rd
Unattributable97ms1ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=G-0JTJS4VF7S&cx=c&gtm=4e64k0h283ms71ms12ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-WLHD85V66ms54ms12ms3rd
A+
Font Loading
4 fonts (197 KB)
PASS
4 fonts (197 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

197 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 500 ms 1.0 s 1.5 s 2.0 s 2.5 s FCP 997 ms LCP 2.5 shttps://www.rug.nl/_definition/shared/fonts/opensans-regular.woff2opensans-regular.woff2 https://www.rug.nl/_definition/shared/fonts/opensans-regular.woff2 — 58.7 KiB — 74 ms — font-display: swaphttps://www.rug.nl/_definition/shared/fonts/icomoon.wofficomoon.woff https://www.rug.nl/_definition/shared/fonts/icomoon.woff — 23.0 KiB — 90 ms — font-display: swaphttps://www.rug.nl/_definition/shared/fonts/opensans-semibold.woff2opensans-semibold.woff2 https://www.rug.nl/_definition/shared/fonts/opensans-semibold.woff2 — 58.7 KiB — 113 ms — font-display: swaphttps://www.rug.nl/_definition/shared/fonts/opensans-bold.woff2opensans-bold.woff2 https://www.rug.nl/_definition/shared/fonts/opensans-bold.woff2 — 56.8 KiB — 104 ms — font-display: swap
opensans-regular.woff2 woff2 swap
Size 59 KB
Load time 74 ms
Start 555 ms
Risk FOUT — text flashes from fallback to web font
icomoon.woff woff swap
Size 23 KB
Load time 90 ms
Start 555 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
opensans-semibold.woff2 woff2 swap
Size 59 KB
Load time 113 ms
Start 555 ms
Risk FOUT — text flashes from fallback to web font
opensans-bold.woff2 woff2 swap
Size 57 KB
Load time 104 ms
Start 582 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)

Fixing the unchecked items could save ~7 KB and ~14 ms

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
Network Waterfall
51 requests over 2713ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s 2.5 s FCP 997 ms LCP 2.5 shttps://rug.nl// https://rug.nl/ — 301 — 163 B — 106 ms — http/1.0https://www.rug.nl/www.rug.nl/ https://www.rug.nl/ — 200 — 9.3 KiB — 162 ms — http/1.1https://www.rug.nl/_definition/shared/css/jquery-smoothness/jquery-ui.min.css?version=2026-03-12www.rug.nl/_definition/shared/css/j... https://www.rug.nl/_definition/shared/css/jquery-smoothness/jquery-ui.min.css?version=2026-03-12 — 200 — 7.9 KiB — 44 ms — http/1.1https://www.rug.nl/_definition/shared/css/styles_v2.css?version=2026-03-12www.rug.nl/_definition/shared/css/s... https://www.rug.nl/_definition/shared/css/styles_v2.css?version=2026-03-12 — 200 — 37.0 KiB — 120 ms — http/1.1https://www.rug.nl/_definition/shared/css/fotorama.css?version=2026-03-12www.rug.nl/_definition/shared/css/f... https://www.rug.nl/_definition/shared/css/fotorama.css?version=2026-03-12 — 200 — 3.5 KiB — 114 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.js?version=2026-03-12 — 200 — 30.3 KiB — 146 ms — http/1.1https://www.rug.nl/_definition/shared/js/ucms.js?version=2026-03-12www.rug.nl/_definition/shared/js/uc... https://www.rug.nl/_definition/shared/js/ucms.js?version=2026-03-12 — 200 — 13.5 KiB — 114 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery-ui.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery-ui.js?version=2026-03-12 — 200 — 64.6 KiB — 183 ms — http/1.1https://www.rug.nl/_definition/shared/js/js-cookie.js?version=2026-03-12www.rug.nl/_definition/shared/js/js... https://www.rug.nl/_definition/shared/js/js-cookie.js?version=2026-03-12 — 200 — 2.1 KiB — 112 ms — http/1.1https://www.rug.nl/_definition/shared/js/md5.js?version=2026-03-12www.rug.nl/_definition/shared/js/md... https://www.rug.nl/_definition/shared/js/md5.js?version=2026-03-12 — 200 — 4.4 KiB — 154 ms — http/1.1https://www.rug.nl/_definition/shared/js/rug-shared.js?version=2026-03-12www.rug.nl/_definition/shared/js/ru... https://www.rug.nl/_definition/shared/js/rug-shared.js?version=2026-03-12 — 200 — 4.1 KiB — 153 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.dialogoptions.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.dialogoptions.js?version=2026-03-12 — 200 — 2.8 KiB — 152 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.dialogoptions-rug.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.dialogoptions-rug.js?version=2026-03-12 — 200 — 1.5 KiB — 154 ms — http/1.1https://www.rug.nl/_definition/shared/js/imagesloaded.js?version=2026-03-12www.rug.nl/_definition/shared/js/im... https://www.rug.nl/_definition/shared/js/imagesloaded.js?version=2026-03-12 — 200 — 2.5 KiB — 181 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.mobile.custom.min.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.mobile.custom.min.js?version=2026-03-12 — 200 — 3.6 KiB — 192 ms — http/1.1https://www.rug.nl/_definition/shared/js/fotorama.js?version=2026-03-12www.rug.nl/_definition/shared/js/fo... https://www.rug.nl/_definition/shared/js/fotorama.js?version=2026-03-12 — 200 — 28.5 KiB — 231 ms — http/1.1https://www.rug.nl/_definition/shared/js/interface.bundle.js?version=2026-03-12www.rug.nl/_definition/shared/js/in... https://www.rug.nl/_definition/shared/js/interface.bundle.js?version=2026-03-12 — 200 — 39.2 KiB — 233 ms — http/1.1https://www.rug.nl/_definition/shared/js/cross-frame.js?version=2026-03-12www.rug.nl/_definition/shared/js/cr... https://www.rug.nl/_definition/shared/js/cross-frame.js?version=2026-03-12 — 200 — 1.4 KiB — 191 ms — http/1.1https://www.rug.nl/_definition/shared/js/contrastmode.jswww.rug.nl/_definition/shared/js/co... https://www.rug.nl/_definition/shared/js/contrastmode.js — 200 — 807 B — 217 ms — http/1.1https://www.rug.nl/_definition/shared/images/logo--en.svgwww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/logo--en.svg — 200 — 17.0 KiB — 47 ms — http/1.1https://www.rug.nl/_definition/shared/js/init-cookies.js?version=2026-03-12www.rug.nl/_definition/shared/js/in... https://www.rug.nl/_definition/shared/js/init-cookies.js?version=2026-03-12 — 200 — 1.0 KiB — 37 ms — http/1.1https://www.rug.nl/medicallibrary/images/verwerken.jpgwww.rug.nl/medicallibrary/images/ve... https://www.rug.nl/medicallibrary/images/verwerken.jpg — 200 — 11.9 KiB — 48 ms — http/1.1https://www.rug.nl/about-ug/policy-and-strategy/recognition-rewards/banner-techniek6.jpgwww.rug.nl/about-ug/policy-and-stra... https://www.rug.nl/about-ug/policy-and-strategy/recognition-rewards/banner-techniek6.jpg — 200 — 614.8 KiB — 382 ms — http/1.1https://www.rug.nl/fse/news/technology/1024-openscience.jpgwww.rug.nl/fse/news/technology/1024... https://www.rug.nl/fse/news/technology/1024-openscience.jpg — 200 — 61.0 KiB — 80 ms — http/1.1https://www.rug.nl/about-ug/images/homepage/cards/0421-instellingsplan-home.jpgwww.rug.nl/about-ug/images/homepage... https://www.rug.nl/about-ug/images/homepage/cards/0421-instellingsplan-home.jpg — 200 — 179.6 KiB — 116 ms — http/1.1https://www.rug.nl/about-ug/latest-news/news/archief2026/nieuwsberichten/0420-wetenschap-werkt-benjaminse2.jpgwww.rug.nl/about-ug/latest-news/new... https://www.rug.nl/about-ug/latest-news/news/archief2026/nieuwsberichten/0420-wetenschap-werkt-benjaminse2.jpg — 200 — 138.5 KiB — 115 ms — http/1.1https://www.rug.nl/magazine/0421-lehmannhome1medium-hv-12407.jpgwww.rug.nl/magazine/0421-lehmannhom... https://www.rug.nl/magazine/0421-lehmannhome1medium-hv-12407.jpg — 200 — 219.5 KiB — 177 ms — http/1.1https://www.googletagmanager.com/gtm.js?id=GTM-WLHD85Vwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-WLHD85V — 200 — 159.0 KiB — 1.8 s — h2https://www.rug.nl/_definition/shared/images/flags/nl.svgwww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/flags/nl.svg — 200 — 867 B — 131 ms — http/1.1https://www.rug.nl/_definition/shared/images/flags/gb.svgwww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/flags/gb.svg — 200 — 1.0 KiB — 131 ms — http/1.1
0 ms 500 ms 1.0 s 1.5 s 2.0 s 2.5 s FCP 997 ms LCP 2.5 shttps://rug.nl// https://rug.nl/ — 301 — 163 B — 106 ms — http/1.0https://www.rug.nl/www.rug.nl/ https://www.rug.nl/ — 200 — 9.3 KiB — 162 ms — http/1.1https://www.rug.nl/_definition/shared/css/jquery-smoothness/jquery-ui.min.css?version=2026-03-12www.rug.nl/_definition/shared/css/j... https://www.rug.nl/_definition/shared/css/jquery-smoothness/jquery-ui.min.css?version=2026-03-12 — 200 — 7.9 KiB — 44 ms — http/1.1https://www.rug.nl/_definition/shared/css/styles_v2.css?version=2026-03-12www.rug.nl/_definition/shared/css/s... https://www.rug.nl/_definition/shared/css/styles_v2.css?version=2026-03-12 — 200 — 37.0 KiB — 120 ms — http/1.1https://www.rug.nl/_definition/shared/css/fotorama.css?version=2026-03-12www.rug.nl/_definition/shared/css/f... https://www.rug.nl/_definition/shared/css/fotorama.css?version=2026-03-12 — 200 — 3.5 KiB — 114 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.js?version=2026-03-12 — 200 — 30.3 KiB — 146 ms — http/1.1https://www.rug.nl/_definition/shared/js/ucms.js?version=2026-03-12www.rug.nl/_definition/shared/js/uc... https://www.rug.nl/_definition/shared/js/ucms.js?version=2026-03-12 — 200 — 13.5 KiB — 114 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery-ui.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery-ui.js?version=2026-03-12 — 200 — 64.6 KiB — 183 ms — http/1.1https://www.rug.nl/_definition/shared/js/js-cookie.js?version=2026-03-12www.rug.nl/_definition/shared/js/js... https://www.rug.nl/_definition/shared/js/js-cookie.js?version=2026-03-12 — 200 — 2.1 KiB — 112 ms — http/1.1https://www.rug.nl/_definition/shared/js/md5.js?version=2026-03-12www.rug.nl/_definition/shared/js/md... https://www.rug.nl/_definition/shared/js/md5.js?version=2026-03-12 — 200 — 4.4 KiB — 154 ms — http/1.1https://www.rug.nl/_definition/shared/js/rug-shared.js?version=2026-03-12www.rug.nl/_definition/shared/js/ru... https://www.rug.nl/_definition/shared/js/rug-shared.js?version=2026-03-12 — 200 — 4.1 KiB — 153 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.dialogoptions.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.dialogoptions.js?version=2026-03-12 — 200 — 2.8 KiB — 152 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.dialogoptions-rug.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.dialogoptions-rug.js?version=2026-03-12 — 200 — 1.5 KiB — 154 ms — http/1.1https://www.rug.nl/_definition/shared/js/imagesloaded.js?version=2026-03-12www.rug.nl/_definition/shared/js/im... https://www.rug.nl/_definition/shared/js/imagesloaded.js?version=2026-03-12 — 200 — 2.5 KiB — 181 ms — http/1.1https://www.rug.nl/_definition/shared/js/jquery.mobile.custom.min.js?version=2026-03-12www.rug.nl/_definition/shared/js/jq... https://www.rug.nl/_definition/shared/js/jquery.mobile.custom.min.js?version=2026-03-12 — 200 — 3.6 KiB — 192 ms — http/1.1https://www.rug.nl/_definition/shared/js/fotorama.js?version=2026-03-12www.rug.nl/_definition/shared/js/fo... https://www.rug.nl/_definition/shared/js/fotorama.js?version=2026-03-12 — 200 — 28.5 KiB — 231 ms — http/1.1https://www.rug.nl/_definition/shared/js/interface.bundle.js?version=2026-03-12www.rug.nl/_definition/shared/js/in... https://www.rug.nl/_definition/shared/js/interface.bundle.js?version=2026-03-12 — 200 — 39.2 KiB — 233 ms — http/1.1https://www.rug.nl/_definition/shared/js/cross-frame.js?version=2026-03-12www.rug.nl/_definition/shared/js/cr... https://www.rug.nl/_definition/shared/js/cross-frame.js?version=2026-03-12 — 200 — 1.4 KiB — 191 ms — http/1.1https://www.rug.nl/_definition/shared/js/contrastmode.jswww.rug.nl/_definition/shared/js/co... https://www.rug.nl/_definition/shared/js/contrastmode.js — 200 — 807 B — 217 ms — http/1.1https://www.rug.nl/_definition/shared/images/logo--en.svgwww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/logo--en.svg — 200 — 17.0 KiB — 47 ms — http/1.1https://www.rug.nl/_definition/shared/js/init-cookies.js?version=2026-03-12www.rug.nl/_definition/shared/js/in... https://www.rug.nl/_definition/shared/js/init-cookies.js?version=2026-03-12 — 200 — 1.0 KiB — 37 ms — http/1.1https://www.rug.nl/medicallibrary/images/verwerken.jpgwww.rug.nl/medicallibrary/images/ve... https://www.rug.nl/medicallibrary/images/verwerken.jpg — 200 — 11.9 KiB — 48 ms — http/1.1https://www.rug.nl/about-ug/policy-and-strategy/recognition-rewards/banner-techniek6.jpgwww.rug.nl/about-ug/policy-and-stra... https://www.rug.nl/about-ug/policy-and-strategy/recognition-rewards/banner-techniek6.jpg — 200 — 614.8 KiB — 382 ms — http/1.1https://www.rug.nl/fse/news/technology/1024-openscience.jpgwww.rug.nl/fse/news/technology/1024... https://www.rug.nl/fse/news/technology/1024-openscience.jpg — 200 — 61.0 KiB — 80 ms — http/1.1https://www.rug.nl/about-ug/images/homepage/cards/0421-instellingsplan-home.jpgwww.rug.nl/about-ug/images/homepage... https://www.rug.nl/about-ug/images/homepage/cards/0421-instellingsplan-home.jpg — 200 — 179.6 KiB — 116 ms — http/1.1https://www.rug.nl/about-ug/latest-news/news/archief2026/nieuwsberichten/0420-wetenschap-werkt-benjaminse2.jpgwww.rug.nl/about-ug/latest-news/new... https://www.rug.nl/about-ug/latest-news/news/archief2026/nieuwsberichten/0420-wetenschap-werkt-benjaminse2.jpg — 200 — 138.5 KiB — 115 ms — http/1.1https://www.rug.nl/magazine/0421-lehmannhome1medium-hv-12407.jpgwww.rug.nl/magazine/0421-lehmannhom... https://www.rug.nl/magazine/0421-lehmannhome1medium-hv-12407.jpg — 200 — 219.5 KiB — 177 ms — http/1.1https://www.googletagmanager.com/gtm.js?id=GTM-WLHD85Vwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-WLHD85V — 200 — 159.0 KiB — 1.8 s — h2https://www.rug.nl/_definition/shared/images/flags/nl.svgwww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/flags/nl.svg — 200 — 867 B — 131 ms — http/1.1https://www.rug.nl/_definition/shared/images/flags/gb.svgwww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/flags/gb.svg — 200 — 1.0 KiB — 131 ms — http/1.1https://www.rug.nl/_definition/shared/fonts/opensans-regular.woff2www.rug.nl/_definition/shared/fonts... https://www.rug.nl/_definition/shared/fonts/opensans-regular.woff2 — 200 — 58.7 KiB — 74 ms — http/1.1https://www.rug.nl/_definition/shared/fonts/icomoon.woffwww.rug.nl/_definition/shared/fonts... https://www.rug.nl/_definition/shared/fonts/icomoon.woff — 200 — 23.0 KiB — 90 ms — http/1.1https://www.rug.nl/_definition/shared/fonts/opensans-semibold.woff2www.rug.nl/_definition/shared/fonts... https://www.rug.nl/_definition/shared/fonts/opensans-semibold.woff2 — 200 — 58.7 KiB — 113 ms — http/1.1https://www.rug.nl/_definition/shared/images/why-groningen-academy-building.jpgwww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/why-groningen-academy-building.jpg — 200 — 177.1 KiB — 195 ms — http/1.1https://www.rug.nl/_definition/shared/fonts/opensans-bold.woff2www.rug.nl/_definition/shared/fonts... https://www.rug.nl/_definition/shared/fonts/opensans-bold.woff2 — 200 — 56.8 KiB — 104 ms — http/1.1https://www.rug.nl/about-ug/latest-news/news/dossiers/circulariteit-collage-web2.pngwww.rug.nl/about-ug/latest-news/new... https://www.rug.nl/about-ug/latest-news/news/dossiers/circulariteit-collage-web2.png — 200 — 633.5 KiB — 379 ms — http/1.1https://www.rug.nl/about-ug/latest-news/news/archief2026/0414-bothhome-fotohermanengbers-de-beeldunie.jpgwww.rug.nl/about-ug/latest-news/new... https://www.rug.nl/about-ug/latest-news/news/archief2026/0414-bothhome-fotohermanengbers-de-beeldunie.jpg — 200 — 379.8 KiB — 248 ms — http/1.1https://www.rug.nl/about-ug/images/homepage/cards/werken-bij-de-rug-klein.jpgwww.rug.nl/about-ug/images/homepage... https://www.rug.nl/about-ug/images/homepage/cards/werken-bij-de-rug-klein.jpg — 200 — 68.2 KiB — 78 ms — http/1.1https://www.rug.nl/about-ug/images/homepage/items/research-support.pngwww.rug.nl/about-ug/images/homepage... https://www.rug.nl/about-ug/images/homepage/items/research-support.png — 200 — 103.5 KiB — 76 ms — http/1.1https://www.rug.nl/about-ug/images/homepage/cards/learning-space-library.jpgwww.rug.nl/about-ug/images/homepage... https://www.rug.nl/about-ug/images/homepage/cards/learning-space-library.jpg — 200 — 463.4 KiB — 283 ms — http/1.1https://www.rug.nl/infonet/medewerkers/actueel/news/6-roossien-3-verkleind.jpgwww.rug.nl/infonet/medewerkers/actu... https://www.rug.nl/infonet/medewerkers/actueel/news/6-roossien-3-verkleind.jpg — 200 — 920.7 KiB — 510 ms — http/1.1https://www.rug.nl/about-ug/latest-news/news/archief2024/nieuwsberichten/agenda-foto-rs12002.jpgwww.rug.nl/about-ug/latest-news/new... https://www.rug.nl/about-ug/latest-news/news/archief2024/nieuwsberichten/agenda-foto-rs12002.jpg — 200 — 444.0 KiB — 279 ms — http/1.1https://www.googletagmanager.com/gtag/js?id=G-0JTJS4VF7S&cx=c&gtm=4e64k0h2www.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-0JTJS4VF7S&cx=c&gtm=4e64k0h2 — 200 — 178.6 KiB — 69 ms — h2https://www.google-analytics.com/analytics.jswww.google-analytics.com/analytics.... https://www.google-analytics.com/analytics.js — 200 — 20.9 KiB — 118 ms — h2https://rug.containers.piwik.pro/d759d682-1760-4f61-8228-ee5bb7baedc3.jsrug.containers.piwik.pro/d759d682-1... https://rug.containers.piwik.pro/d759d682-1760-4f61-8228-ee5bb7baedc3.js — 200 — 71.4 KiB — 159 ms — h2https://pagead2.googlesyndication.com/ccm/collect?rcb=9&frm=0&ae=g&en=page_view&dl=https%3A%2F%2Fwww.rug.nl%2F&scrsrc=www.googletagmanager.com&rnd=750668082.1776807546&navt=n&npa=1&ep.ads_data_redaction=0&gtm=45He64k0h2v840329442za200zd840329442xea&gcs=G101&gcd=13p3t3p2p5l1&dma_cps=-&dma=1&tag_exp=0~115938466~115938468~117266400&apve=1&apvf=f&apvc=1&tft=1776807545886&tfd=2359pagead2.googlesyndication.com/ccm/c... https://pagead2.googlesyndication.com/ccm/collect?rcb=9&frm=0&ae=g&en=page_view&dl=https%3A%2F%2Fwww.rug.nl%2F&scrsrc=www.googletagmanager.com&rnd=750668082.1776807546&navt=n&npa=1&ep.ads_data_redaction=0&gtm=45He64k0h2v840329442za200zd840329442xea&gcs=G101&gcd=13p3t3p2p5l1&dma_cps=-&dma=1&tag_exp=0~115938466~115938468~117266400&apve=1&apvf=f&apvc=1&tft=1776807545886&tfd=2359 — 200 — 21 B — 154 ms — h3https://region1.google-analytics.com/g/collect?v=2&tid=G-0JTJS4VF7S&gtm=45je64k0h2v9103444992z8840329442za20gzb840329442zd840329442&_p=1776807543971&gcs=G101&gcd=13p3t3p2p5l1&npa=1&dma_cps=-&dma=1&are=1&cid=2018941288.1776807546&frm=0&pscdl=denied&rcb=1&sr=800x600&uaa=x86&uab=64&uafvl=Chromium%3B147.0.7727.101%7CNot.A%252FBrand%3B8.0.0.0&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115938466~115938468~117266401&dl=https%3A%2F%2Fwww.rug.nl%2F&dp=%2F&sid=1776807546&sct=1&seg=0&dt=Top%20100%20University%20%7C%20University%20of%20Groningen&en=page_view&_fv=1&_nsi=1&_ss=1&tfd=2508region1.google-analytics.com/g/coll... https://region1.google-analytics.com/g/collect?v=2&tid=G-0JTJS4VF7S&gtm=45je64k0h2v9103444992z8840329442za20gzb840329442zd840329442&_p=1776807543971&gcs=G101&gcd=13p3t3p2p5l1&npa=1&dma_cps=-&dma=1&are=1&cid=2018941288.1776807546&frm=0&pscdl=denied&rcb=1&sr=800x600&uaa=x86&uab=64&uafvl=Chromium%3B147.0.7727.101%7CNot.A%252FBrand%3B8.0.0.0&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115938466~115938468~117266401&dl=https%3A%2F%2Fwww.rug.nl%2F&dp=%2F&sid=1776807546&sct=1&seg=0&dt=Top%20100%20University%20%7C%20University%20of%20Groningen&en=page_view&_fv=1&_nsi=1&_ss=1&tfd=2508 — 204 — 546 B — 69 ms — h2https://www.google-analytics.com/j/collect?v=1&_v=j102&aip=1&a=1744194297&t=pageview&_s=1&dl=https%3A%2F%2Fwww.rug.nl%2F&ul=en-us&dt=Top%20100%20University%20%7C%20University%20of%20Groningen&sr=800x600&vp=1350x940&_u=YADAAEABAAAAICAAIg~&cid=2018941288.1776807546&tid=UA-773007-1&_gid=1809429322.1776807546&_slc=1&gtm=45He64k0h2n81WLHD85Vv840329442za200zd840329442&gcs=G101&gcd=13p3t3p2p5l1&dma_cps=-&dma=1&tag_exp=0~115938466~115938468~117266400&npa=1&z=1379236178www.google-analytics.com/j/collect?... https://www.google-analytics.com/j/collect?v=1&_v=j102&aip=1&a=1744194297&t=pageview&_s=1&dl=https%3A%2F%2Fwww.rug.nl%2F&ul=en-us&dt=Top%20100%20University%20%7C%20University%20of%20Groningen&sr=800x600&vp=1350x940&_u=YADAAEABAAAAICAAIg~&cid=2018941288.1776807546&tid=UA-773007-1&_gid=1809429322.1776807546&_slc=1&gtm=45He64k0h2n81WLHD85Vv840329442za200zd840329442&gcs=G101&gcd=13p3t3p2p5l1&dma_cps=-&dma=1&tag_exp=0~115938466~115938468~117266400&npa=1&z=1379236178 — 200 — 449 B — 25 ms — h2https://rug.containers.piwik.pro/ppms.jsrug.containers.piwik.pro/ppms.js https://rug.containers.piwik.pro/ppms.js — 200 — 26.0 KiB — 45 ms — h2https://rug.piwik.pro/ppms.phprug.piwik.pro/ppms.php https://rug.piwik.pro/ppms.php — 202 — 0 B — 101 ms — h2https://www.rug.nl/_definition/shared/images/favicons/icon.icowww.rug.nl/_definition/shared/image... https://www.rug.nl/_definition/shared/images/favicons/icon.ico — 200 — 7.3 KiB — 41 ms — http/1.1
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 347ms · 347KB · €4/mo
www.rug.nl
Other
Optional
Execution 101ms
Transfer 9 KB
Monthly Cost €1/mo
Unattributable
Other
Optional
Execution 97ms
Transfer 0 KB
Monthly Cost €1/mo
Google Tag Manager
Tag Manager
Optional
Execution 83ms
Transfer 179 KB
Unused 38%
Monthly Cost €1/mo
Google Tag Manager
Tag Manager
Optional
Execution 66ms
Transfer 159 KB
Unused 42%
Monthly Cost €1/mo

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

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.

Send Feedback