Performance

· 15 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

SEO

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

633 ms

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

1.71 s

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

27 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.

676 ms

Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.

2.00 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

6 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

40 resources · 1.5 MB · 199 KB savings available

FIX

40 resources · 1.5 MB · 199 KB savings available

Page weight 501 KB over 1MB target

Got: 1.5 MB Expected: ≤ 1 MB

~199 KB of savings available

39 third-party resources (100% of weight)

1 resources over 200KB

40 resources · 1.5 MiB · 39 third-party 501.1 KiB over 1MB target

Image 50% · 762.7 KiB

JavaScript 36% · 556.1 KiB

Font 7% · 111.4 KiB

CSS 6% · 84.2 KiB

Document 1% · 9.2 KiB

Other 0% · 1.5 KiB

~199.0 KiB of savings available

Remove unused JavaScript: 199.0 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

40 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, 40 requests

REVIEW

1.5 MB transferred, 40 requests

Page weighs 3.1 MB (1.5 MB transferred)

JavaScript is 556 KB — consider code splitting or lazy loading

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

Got: 556 KB

40 HTTP requests

Estimated 0.31 g CO2 per page load

1.5 MB transferred

40 requests

0.31 g CO2 per page load

Images 757.8 KiB 50%

JavaScript 556.1 KiB 36%

Fonts 111.4 KiB 7%

CSS 84.2 KiB 6%

HTML 7.2 KiB 0%

Other 5.0 KiB 0%

Other 1.9 KiB 0%

Other 1.3 KiB 0%

0 2.4 MB 4.9 MB

Approaching limit

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

Image Optimization

Action

10 images, 0 KB saveable

REVIEW

10 images, 0 KB saveable

https://www.universiteitleiden.nl/binaries/content... is missing width/height — may cause layout shift

Set explicit width and height to prevent CLS.

https://www.universiteitleiden.nl/binaries/content... is missing width/height — may cause layout shift

Set explicit width and height to prevent CLS.

10 images 758 KB

0 oversized -0 KB

8 legacy format

2 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

JS Bundles

Action

16 scripts, 199 KB unused

REVIEW

16 scripts, 199 KB unused

https://www.googletagmanager.com/gtm.js?id=GTM-P7S...: 70 KB unused (40%)