Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.

SCORE

GRADE

FIX

REVIEW

PASS

INFO

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

Mobile Desktop

Performance

Accessibility

Best Practices

100

SEO

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

4.57 s

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

9.63 s

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

350 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.

6.34 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.

9.73 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

8 PASS 4 REVIEW 3 FIX

Third-Party Impact

Action

100% third-party, 0 ms blocking

FIX

100% third-party, 0 ms blocking

Third-party code accounts for 100% of page weight (1.5 MiB of 1.5 MiB)

Third-party blocking time is low (0 ms)

100%

First-party Third-party

Page Weight Inventory

Action

57 resources · 1.5 MB · 77 KB savings available

FIX

57 resources · 1.5 MB · 77 KB savings available

Page weight 530 KB over 1MB target

Got: 1.5 MB Expected: ≤ 1 MB

~77 KB of savings available

56 third-party resources (100% of weight)

57 resources · 1.5 MiB · 56 third-party 529.7 KiB over 1MB target

Image 55% · 857.4 KiB

JavaScript 24% · 369.2 KiB

Font 14% · 221.0 KiB

CSS 4% · 69.2 KiB

Document 2% · 34.1 KiB

Other 0% · 2.8 KiB

~76.6 KiB of savings available

Remove unused JavaScript: 76.6 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

57 resources			1.5 MiB

HTTP Caching

Action

No cache headers

FIX

No cache headers

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.

Page Weight Budget

1.5 MB transferred, 57 requests

REVIEW

1.5 MB transferred, 57 requests

Page weighs 3.1 MB (1.5 MB transferred)

Fonts are 221 KB — consider subsetting or using system fonts

Subset fonts to include only used characters, or switch to system font stacks.

Got: 221 KB

57 HTTP requests

Estimated 0.32 g CO2 per page load

1.5 MB transferred

57 requests

0.32 g CO2 per page load

Images 841.5 KiB 54%

JavaScript 368.1 KiB 24%

Fonts 221.0 KiB 14%

CSS 69.2 KiB 4%

HTML 34.1 KiB 2%

Other 16.0 KiB 1%

Other 3.2 KiB 0%

Other 724 B 0%

Other 0 B 0%

0 2.4 MB 4.9 MB

Approaching limit

Subset fonts to include only used characters, or switch to system font stacks.

Why this matters

Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).

Source: web.dev font loading

JS Execution Cost

Action

1844ms total JS execution

REVIEW

1844ms total JS execution

https://consent.cookiebot.eu/376e78a0-37fc-48a7-9d...: 621ms CPU time

https://www.tudelft.nl/_assets/f6b877d73456607fbfa...: 432ms CPU time

https://www.tudelft.nl/: 311ms CPU time

Unattributable: 278ms CPU time

https://consent.cookiebot.eu/uc.js: 119ms CPU time

Third-party scripts: 1844ms (100% of total)

Main Thread Breakdown

Script Evaluation 36% Style & Layout 20% Other 18% Parse HTML & CSS 18% Script Parsing & Compilation 6%

Script	Total	Scripting	Parse/Compile	Party
https://consent.cookiebot.eu/376e78a0-37fc-48a7-9d73-a58eb8a9c2af/cc.js?renew=false&referer=www.tudelft.nl&dnt=false&init=false&culture=nl	621ms	239ms	33ms	3rd
https://www.tudelft.nl/_assets/f6b877d73456607fbfa2de3e3c5fd420/JavaScript/dist.javascripts.350f3e01aa.min.js?1776230288	432ms	223ms	35ms	3rd
https://www.tudelft.nl/	311ms	24ms	11ms	3rd
Unattributable	278ms	14ms	0ms	3rd
https://consent.cookiebot.eu/uc.js	119ms	98ms	11ms	3rd
https://siteimproveanalytics.com/js/siteanalyze_6005654.js	83ms	55ms	21ms	3rd

JS Bundles

12 scripts, 77 KB unused

REVIEW

12 scripts, 77 KB unused

https://www.tudelft.nl/_assets/f6b877d73456607fbfa...: 77 KB unused (66%)

Consider code splitting or tree shaking to reduce unused code.

Total unused JavaScript: 77 KB

77 KB unused JavaScript

Downloaded but never executed on this page.

Script	Size	Unused	Minified	Party
https://www.tudelft.nl/_assets/f6b877d73456607fbfa2de3e3c5fd420/JavaScript/dist.javascripts.350f3e01aa.min.js?1776230288	116 KB	77 KB (66%)	✓	3rd
https://www.tudelft.nl/typo3temp/assets/js/222a0289ea16d2c543939f3cf084853a.js?1776230457	1 KB	—	✓	3rd
https://siteimproveanalytics.com/js/siteanalyze_6005654.js	40 KB	—	✓	3rd
https://consent.cookiebot.eu/uc.js	30 KB	—	✓	3rd
https://consent.cookiebot.eu/376e78a0-37fc-48a7-9d73-a58eb8a9c2af/cc.js?renew=false&referer=www.tudelft.nl&dnt=false&init=false&culture=nl	94 KB	—	✓	3rd
https://www.browsealoud.com/plus/scripts/3.1.0/ba.js	2 KB	—	✓	3rd
https://plus.browsealoud.com/js/urlinfo/www.tudelft.nl.js	1 KB	—	✓	3rd
https://www.browsealoud.com/modules/3.11.0/browsealoud.js	41 KB	—	✓	3rd
https://plus.browsealoud.com/js/urlinfo/www.tudelft.nl.js	0 KB	—	✓	3rd
https://www.browsealoud.com/modules/3.11.0/4916.dd13ed0cd26117b33f9d.js	30 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

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

All text resources are properly compressed.

Image Optimization

30 images, 0 KB saveable

PASS

30 images, 0 KB saveable

All images are well-optimized

30 images 841 KB

0 oversized -0 KB

3 legacy format

0 missing dimensions CLS risk

A+

Font Loading

4 fonts (221 KB)

PASS

4 fonts (221 KB)

4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

221 KB total

Render-blocking

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline

Transfer FOIT (block) FOUT (swap)

RobotoSlab-Regular.woff2 woff2 swap

Size 70 KB

Load time 113 ms

Start 829 ms

Risk FOUT — text flashes from fallback to web font

icons.1768915092.woff woff swap

Size 9 KB

Load time 204 ms

Start 829 ms

Risk FOUT — text flashes from fallback to web font

Convert to woff2 for ~30% smaller file size

RobotoSlab-Medium.woff2 woff2 swap

Size 72 KB

Load time 181 ms

Start 830 ms

Risk FOUT — text flashes from fallback to web font

RobotoSlab-Light.woff2 woff2 swap

Size 70 KB

Load time 184 ms

Start 830 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 ~3 KB and ~6 ms

A+

Resource Caching

All resources properly cached

PASS

All resources properly cached

No caching issues found

All static resources have appropriate caching headers.

A+

Critical Rendering Path

No render-blocking resources

PASS

No render-blocking resources

No render-blocking resources detected

A+

Resource Hints

No optimization needed

PASS

No optimization needed

No resource hint issues

A+

Render-Blocking Resources

No render-blocking resources detected

PASS

No render-blocking resources detected

No render-blocking resources detected in <head>

A+

Third-Party Resources

No third-party resources detected

PASS

No third-party resources detected

Network Waterfall

57 requests over 1558ms

INFO

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 1844ms · 313KB · €20/mo

Script	Category	Execution	Transfer	Unused	Monthly Cost	Verdict
consent.cookiebot.eu consent.cookiebot.eu	Other	621ms	94 KB	—	€7/mo	Costly
www.tudelft.nl www.tudelft.nl	Other	432ms	116 KB	66%	€5/mo	Costly
www.tudelft.nl www.tudelft.nl	Other	311ms	33 KB	—	€3/mo	Costly
Unattributable Unattributable	Other	278ms	0 KB	—	€3/mo	Costly
consent.cookiebot.eu consent.cookiebot.eu	Other	119ms	30 KB	—	€1/mo	Optional
siteimproveanalytics.com siteimproveanalytics.com	Other	83ms	40 KB	—	€1/mo	Optional

consent.cookiebot.eu

Other

Costly

Execution 621ms

Transfer 94 KB

Monthly Cost €7/mo

www.tudelft.nl

Other

Costly

Execution 432ms

Transfer 116 KB

Unused 66%

Monthly Cost €5/mo

www.tudelft.nl

Other

Costly

Execution 311ms

Transfer 33 KB

Monthly Cost €3/mo

Unattributable

Other

Costly

Execution 278ms

Transfer 0 KB

Monthly Cost €3/mo

consent.cookiebot.eu

Other

Optional

Execution 119ms

Transfer 30 KB

Monthly Cost €1/mo

siteimproveanalytics.com

Other

Optional

Execution 83ms

Transfer 40 KB

Monthly Cost €1/mo

These scripts may cost more than they're worth

consent.cookiebot.eu adds 621ms and costs ~€7/month
www.tudelft.nl adds 432ms and costs ~€5/month
www.tudelft.nl adds 311ms and costs ~€3/month
Unattributable adds 278ms 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

consent.cookiebot.eu takes 621ms 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

www.tudelft.nl takes 432ms 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.tudelft.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.tudelft.nl takes 311ms 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 278ms 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

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.