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https://xs4all.nl

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
92
GRADE
A
FIX
2
REVIEW
2
PASS
11
INFO
2

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

Mobile Desktop
98
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
92
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.
92
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.

1.85 s

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

2.00 s

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

0 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.

1.85 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.

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
17
11 PASS 2 REVIEW 2 FIX
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 (111.9 KiB of 112.0 KiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
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
8 images, 0 KB saveable
REVIEW
8 images, 0 KB saveable
Warning::
https://www.xs4all.nl/assets/images/header-willemi... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.xs4all.nl/assets/images/xs4all-kpn.svg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
8 images 33 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

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

Green Hosting

No green hosting detected

A+
Page Weight Budget
112 KB transferred, 18 requests
PASS
112 KB transferred, 18 requests
Info::
Page weighs 148 KB (112 KB transferred)
Info::
18 HTTP requests
Info::
Estimated 0.02 g CO2 per page load
112 KB / 2.4 MB budget
112 KB transferred
18 requests
0.02 g CO2 per page load
Fonts 47.0 KiB 42%
Images 32.6 KiB 29%
Other 15.5 KiB 14%
CSS 9.5 KiB 9%
HTML 4.7 KiB 4%
JavaScript 2.6 KiB 2%
0 2.4 MB 4.9 MB
Under budget
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
268ms total JS execution
PASS
268ms total JS execution
Info::
Unattributable: 144ms CPU time
Info::
https://www.xs4all.nl/: 124ms CPU time
Warning::
Third-party scripts: 268ms (100% of total)

Main Thread Breakdown

Other 53% Style & Layout 29% Rendering 8% Script Evaluation 5% Parse HTML & CSS 5%
ScriptTotalScriptingParse/CompileParty
Unattributable144ms5ms0ms3rd
https://www.xs4all.nl/124ms4ms0ms3rd
A+
Font Loading
1 fonts (47 KB)
PASS
1 fonts (47 KB)
Info::
1 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

1

47 KB total

Render-blocking

0

of 1

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 FCP 1.8 s LCP 2.0 shttps://www.xs4all.nl/assets/fonts/TiemposHeadlineWeb-Light.woff2TiemposHeadlineWeb-Ligh... https://www.xs4all.nl/assets/fonts/TiemposHeadlineWeb-Light.woff2 — 47.0 KiB — 6 ms — font-display: swap
TiemposHeadlineWeb-Ligh... woff2 swap
Size 47 KB
Load time 6 ms
Start 241 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+
JS Bundles
2 scripts, 0 KB unused
PASS
2 scripts, 0 KB unused
0 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.xs4all.nl/main-footer.js1 KB—✓3rd
https://www.xs4all.nl/main-header.js2 KB—✓3rd
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
Page Weight Inventory
18 resources · 112 KB · 0 KB savings available
PASS
18 resources · 112 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 112 KB
Warning::
17 third-party resources (100% of weight)
18 resources · 112.0 KiB · 17 third-party Within 1MB page-weight target
Image 43% · 48.0 KiB
Font 42% · 47.0 KiB
CSS 9% · 9.5 KiB
Document 4% · 4.8 KiB
JavaScript 2% · 2.6 KiB
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
18 requests over 332ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s FCP 1.8 s LCP 2.0 shttps://xs4all.nl// https://xs4all.nl/ — 301 — 84 B — 162 ms — h2https://www.xs4all.nl/www.xs4all.nl/ https://www.xs4all.nl/ — 200 — 4.7 KiB — 18 ms — h2https://www.xs4all.nl/app.csswww.xs4all.nl/app.css https://www.xs4all.nl/app.css — 200 — 2.5 KiB — 12 ms — h2https://www.xs4all.nl/content.csswww.xs4all.nl/content.css https://www.xs4all.nl/content.css — 200 — 2.5 KiB — 15 ms — h2https://www.xs4all.nl/main-header.csswww.xs4all.nl/main-header.css https://www.xs4all.nl/main-header.css — 200 — 2.1 KiB — 12 ms — h2https://www.xs4all.nl/main-footer.csswww.xs4all.nl/main-footer.css https://www.xs4all.nl/main-footer.css — 200 — 2.4 KiB — 13 ms — h2https://www.xs4all.nl/assets/images/xs4all-emblem-yellow.svgwww.xs4all.nl/assets/images/xs4all-... https://www.xs4all.nl/assets/images/xs4all-emblem-yellow.svg — 200 — 1.5 KiB — 16 ms — h2https://www.xs4all.nl/assets/images/header-karima-992px.webpwww.xs4all.nl/assets/images/header-... https://www.xs4all.nl/assets/images/header-karima-992px.webp — 200 — 7.2 KiB — 124 ms — h2https://www.xs4all.nl/assets/images/header-willemijn-992px.webpwww.xs4all.nl/assets/images/header-... https://www.xs4all.nl/assets/images/header-willemijn-992px.webp — 200 — 17.0 KiB — 39 ms — h2https://www.xs4all.nl/assets/images/xs4all-kpn.svgwww.xs4all.nl/assets/images/xs4all-... https://www.xs4all.nl/assets/images/xs4all-kpn.svg — 200 — 1.2 KiB — 16 ms — h2https://www.xs4all.nl/main-footer.jswww.xs4all.nl/main-footer.js https://www.xs4all.nl/main-footer.js — 200 — 750 B — 14 ms — h2https://www.xs4all.nl/assets/images/facebook_gray-700_60.svgwww.xs4all.nl/assets/images/faceboo... https://www.xs4all.nl/assets/images/facebook_gray-700_60.svg — 200 — 1.6 KiB — 7 ms — h2https://www.xs4all.nl/assets/images/twitter_gray-700_60.svgwww.xs4all.nl/assets/images/twitter... https://www.xs4all.nl/assets/images/twitter_gray-700_60.svg — 200 — 1.3 KiB — 10 ms — h2https://www.xs4all.nl/assets/images/youtube_gray-700_60.svgwww.xs4all.nl/assets/images/youtube... https://www.xs4all.nl/assets/images/youtube_gray-700_60.svg — 200 — 1.3 KiB — 8 ms — h2https://www.xs4all.nl/assets/images/news-rss_gray-700_60.svgwww.xs4all.nl/assets/images/news-rs... https://www.xs4all.nl/assets/images/news-rss_gray-700_60.svg — 200 — 1.6 KiB — 9 ms — h2https://www.xs4all.nl/assets/fonts/TiemposHeadlineWeb-Light.woff2www.xs4all.nl/assets/fonts/TiemposH... https://www.xs4all.nl/assets/fonts/TiemposHeadlineWeb-Light.woff2 — 200 — 47.0 KiB — 6 ms — h2https://www.xs4all.nl/main-header.jswww.xs4all.nl/main-header.js https://www.xs4all.nl/main-header.js — 200 — 1.9 KiB — 9 ms — h2https://www.xs4all.nl/favicon.icowww.xs4all.nl/favicon.ico https://www.xs4all.nl/favicon.ico — 200 — 15.4 KiB — 8 ms — h2
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 268ms · 5KB · €3/mo
Unattributable
Other
Optional
Execution 144ms
Transfer 0 KB
Monthly Cost €2/mo
www.xs4all.nl
Other
Optional
Execution 124ms
Transfer 5 KB
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.

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