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Contrast Checker

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https://overheid.nl

Performance

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

SCORE

80

GRADE

B

FIX

3

REVIEW

3

PASS

9

INFO

2

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

52

Performance

97

Accessibility

100

Best Practices

92

SEO

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

2.07 s

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

7.06 s

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

775 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.

5.02 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.

7.06 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

17

9 PASS 3 REVIEW 3 FIX

D

Page Weight Budget

Action

2.2 MB transferred, 22 requests

FIX

2.2 MB transferred, 22 requests

Page weighs 4.5 MB (2.2 MB transferred)

Images are 1.2 MB — compress or use modern formats

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Got: 1.2 MB

JavaScript is 770 KB — consider code splitting or lazy loading

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

Got: 770 KB

22 HTTP requests

Estimated 0.47 g CO2 per page load

2.2 MB transferred

22 requests

0.47 g CO2 per page load

Images 1.2 MiB 56%

JavaScript 770.5 KiB 34%

Fonts 143.4 KiB 6%

CSS 88.2 KiB 4%

HTML 6.2 KiB 0%

Other 3.6 KiB 0%

Other 0 B 0%

0 2.4 MB 4.9 MB

Approaching limit

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

F

JS Bundles

Action

4 scripts, 572 KB unused

FIX

4 scripts, 572 KB unused

https://overheid.nl/sites/default/files/js/js_uOMZ...: 497 KB unused (82%)

Consider code splitting or tree shaking to reduce unused code.

https://overheid.nl/sites/default/files/js/js_RGZD...: 40 KB unused (66%)

Consider code splitting or tree shaking to reduce unused code.

https://koop.piwik.pro/containers/042a8a3e-7692-4e...: 36 KB unused (44%)

Consider code splitting or tree shaking to reduce unused code.

Total unused JavaScript: 572 KB

572 KB unused JavaScript

Downloaded but never executed on this page.

Script	Size	Unused	Minified	Party
https://overheid.nl/sites/default/files/js/js_uOMZ6Shqc42Sf1wo7NmMYjjwm2inS8gWpjvbFOSqHho.js?scope=header&delta=0&language=nl&theme=koopoverheid_theme&include=eJxtytEJwCAMBcCFBEcSU18T0ZKSxILbd4D2-26o3vrABL2VEFzIPJXqTOMrHnuCV28oh_vfCDElgiVfzPCA5ajcz_0CnGop0Q	603 KB	497 KB (82%)	✓	1st
https://overheid.nl/sites/default/files/js/js_RGZDxG-0U-PNstrwDRvFXIEZx7FI45u607ekWWKg7vk.js?scope=footer&delta=0&language=nl&theme=koopoverheid_theme&include=eJxtytEJwCAMBcCFBEcSU18T0ZKSxILbd4D2-26o3vrABL2VEFzIPJXqTOMrHnuCV28oh_vfCDElgiVfzPCA5ajcz_0CnGop0Q	61 KB	40 KB (66%)	✓	1st
https://koop.piwik.pro/containers/042a8a3e-7692-4e18-8abf-c3034df672d0.js?use_secure_cookies	81 KB	36 KB (44%)	✓	3rd
https://koop.piwik.pro/ppms.js	26 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

D

Page Weight Inventory

Action

22 resources · 2.2 MB · 572 KB savings available

FIX

22 resources · 2.2 MB · 572 KB savings available

Page weight 1.2 MB over 1MB target

Got: 2.2 MB Expected: ≤ 1 MB

~572 KB of savings available

4 third-party resources (5% of weight)

3 resources over 200KB

22 resources · 2.2 MiB · 4 third-party 1.2 MiB over 1MB target

Image 56% · 1.2 MiB

JavaScript 34% · 770.5 KiB

Font 6% · 143.4 KiB

CSS 4% · 88.2 KiB

Document 0% · 6.2 KiB

~572.4 KiB of savings available

Remove unused JavaScript: 572.4 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

22 resources			2.2 MiB

B

Image Optimization

9 images, 0 KB saveable

REVIEW

9 images, 0 KB saveable

https://overheid.nl/themes/contrib/koopoverheid_th... is missing width/height — may cause layout shift

Set explicit width and height to prevent CLS.

9 images 1.2 MB

0 oversized -0 KB

9 legacy format

1 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

C

JS Execution Cost

Action

1346ms total JS execution

REVIEW

1346ms total JS execution

https://overheid.nl/sites/default/files/js/js_uOMZ...: 723ms CPU time

Unattributable: 202ms CPU time

https://koop.piwik.pro/containers/042a8a3e-7692-4e...: 196ms CPU time

https://overheid.nl/sites/default/files/js/js_RGZD...: 153ms CPU time

https://overheid.nl/: 72ms CPU time

Third-party scripts: 398ms (30% of total)

Main Thread Breakdown

Script Evaluation 51% Script Parsing & Compilation 19% Other 15% Style & Layout 7% Garbage Collection 5% Parse HTML & CSS 3%

Script	Total	Scripting	Parse/Compile	Party
https://overheid.nl/sites/default/files/js/js_uOMZ6Shqc42Sf1wo7NmMYjjwm2inS8gWpjvbFOSqHho.js?scope=header&delta=0&language=nl&theme=koopoverheid_theme&include=eJxtytEJwCAMBcCFBEcSU18T0ZKSxILbd4D2-26o3vrABL2VEFzIPJXqTOMrHnuCV28oh_vfCDElgiVfzPCA5ajcz_0CnGop0Q	723ms	481ms	209ms	1st
Unattributable	202ms	6ms	0ms	3rd
https://koop.piwik.pro/containers/042a8a3e-7692-4e18-8abf-c3034df672d0.js?use_secure_cookies	196ms	143ms	32ms	3rd
https://overheid.nl/sites/default/files/js/js_RGZDxG-0U-PNstrwDRvFXIEZx7FI45u607ekWWKg7vk.js?scope=footer&delta=0&language=nl&theme=koopoverheid_theme&include=eJxtytEJwCAMBcCFBEcSU18T0ZKSxILbd4D2-26o3vrABL2VEFzIPJXqTOMrHnuCV28oh_vfCDElgiVfzPCA5ajcz_0CnGop0Q	153ms	56ms	22ms	1st
https://overheid.nl/	72ms	7ms	2ms	1st

C

Green Hosting

Action

Whether the site is served from green-energy infrastructure

REVIEW

Green Hosting

No green hosting detected

A+

Third-Party Impact

5% third-party, 0 ms blocking

PASS

5% third-party, 0 ms blocking

Third-party code accounts for 5% of page weight (106.7 KiB of 2.2 MiB)

Third-party blocking time is low (0 ms)

95%

First-party Third-party

A+

Text Compression

All text resources are compressed

PASS

All text resources are compressed

All text resources are compressed

All text resources are properly compressed.

A+

Font Loading

2 fonts (143 KB)

PASS

2 fonts (143 KB)

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

Web fonts

2

143 KB total

Render-blocking

0

of 2

Dominant font-display

swap

Most common across fonts

Font loading timeline

Transfer FOIT (block) FOUT (swap)

ROsanswebtextregular.woff woff swap

Size 75 KB

Load time 72 ms

Start 670 ms

Risk FOUT — text flashes from fallback to web font

Convert to woff2 for ~30% smaller file size

ROsanswebtextbold.woff woff swap

Size 68 KB

Load time 74 ms

Start 670 ms

Risk FOUT — text flashes from fallback to web font

Convert to woff2 for ~30% smaller file size

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 ~43 KB and ~86 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

A+

HTTP Caching

max-age=31536000 (52 weeks)

PASS

max-age=31536000 (52 weeks)

Cache-Control header is set

Got: max-age=31536000, public

Effective TTL: 52 weeks (max-age=31536000)

ETag present — enables conditional (304) responses

Last-Modified header present

Cache-Control

max-age=31536000, public

Directive	Value	Meaning
max-age	31536000	Cache for 52 weeks
public	—	Any cache may store this response

Effective TTL: 31536000 seconds

Network Waterfall

22 requests over 860ms

INFO

HTML JavaScript CSS Images Fonts XHR/Fetch Other

Third-Party Script Cost

Per-script blocking time, transfer cost, and cache headers

INFO

30% of JavaScript execution is third-party

First-party Third-party 398ms · 81KB · €4/mo

Script	Category	Execution	Transfer	Unused	Monthly Cost	Verdict
Unattributable Unattributable	Other	202ms	0 KB	—	€2/mo	Costly
koop.piwik.pro koop.piwik.pro	Other	196ms	81 KB	44%	€2/mo	Optional

Unattributable

Other

Costly

Execution 202ms

Transfer 0 KB

Monthly Cost €2/mo

koop.piwik.pro

Other

Optional

Execution 196ms

Transfer 81 KB

Unused 44%

Monthly Cost €2/mo

These scripts may cost more than they're worth

Unattributable adds 202ms and costs ~€2/month

Unattributable takes 202ms 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.

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