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https://fourmilab.ch

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
97
GRADE
A+
FIX
1
REVIEW
2
PASS
10
INFO
2

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

Mobile Desktop
0
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
71
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
96
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
91
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.

0 ms

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

0 ms

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.

0 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.

0 ms

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
10 PASS 2 REVIEW 1 FIX
D
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.
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present

No Cache-Control header

Adding a Cache-Control header can significantly improve repeat-visit performance.

B
Image Optimization
8 images, 0 KB saveable
REVIEW
8 images, 0 KB saveable
Info::
All images are well-optimized
8 images 14 KB
0 oversized -0 KB
8 legacy format
0 missing dimensions CLS risk
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
22 KB transferred, 17 requests
PASS
22 KB transferred, 17 requests
Info::
Page weighs 40 KB (22 KB transferred)
Info::
17 HTTP requests
Info::
Estimated 0.00 g CO2 per page load
22 KB / 2.4 MB budget
22 KB transferred
17 requests
0.00 g CO2 per page load
Images 14.1 KiB 64%
HTML 6.1 KiB 28%
CSS 978 B 4%
Other 865 B 4%
0 2.4 MB 4.9 MB
Under budget
A+
Third-Party Impact
No third-party resources
PASS
No third-party resources
Info::
No third-party resources detected
No third-party resources detected — all resources are first-party.
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
66ms total JS execution
PASS
66ms total JS execution
Info::
Unattributable: 66ms CPU time
Warning::
Third-party scripts: 66ms (100% of total)

Main Thread Breakdown

Other 54% Style & Layout 30% Parse HTML & CSS 8% Rendering 4% Script Evaluation 4%
ScriptTotalScriptingParse/CompileParty
Unattributable66ms1ms0ms3rd
A+
Font Loading
No web fonts (system fonts)
PASS
No web fonts (system fonts)
Info::
No web fonts loaded — system fonts are fastest
No web fonts loaded — system fonts are optimal.
A+
JS Bundles
No JavaScript
PASS
No JavaScript
Info::
No JavaScript bundles
No JavaScript files loaded.
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
17 resources · 22 KB · 0 KB savings available
PASS
17 resources · 22 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 22 KB
17 resources · 22.1 KiB · 0 third-party Within 1MB page-weight target
Image 68% · 15.0 KiB
Document 28% · 6.1 KiB
CSS 4% · 978 B
Network Waterfall
17 requests over 328ms
INFO
0 ms 200 mshttps://fourmilab.ch// https://fourmilab.ch/ — 200 — 917 B — 96 ms — h2https://fourmilab.ch/nav/topics/nav.css/nav/topics/nav.css https://fourmilab.ch/nav/topics/nav.css — 200 — 978 B — 33 ms — h2https://fourmilab.ch/nav/titre.html/nav/titre.html https://fourmilab.ch/nav/titre.html — 200 — 767 B — 34 ms — h2https://fourmilab.ch/nav/browser.html/nav/browser.html https://fourmilab.ch/nav/browser.html — 200 — 428 B — 33 ms — h2https://fourmilab.ch/images/logo/swlogo.png/images/logo/swlogo.png https://fourmilab.ch/images/logo/swlogo.png — 200 — 2.5 KiB — 33 ms — h2https://fourmilab.ch/images/buttons/chrome_home.gif/images/buttons/chrome_home.gif https://fourmilab.ch/images/buttons/chrome_home.gif — 200 — 1.6 KiB — 34 ms — h2https://fourmilab.ch/images/buttons/chrome_find.gif/images/buttons/chrome_find.gif https://fourmilab.ch/images/buttons/chrome_find.gif — 200 — 1.5 KiB — 35 ms — h2https://fourmilab.ch/images/buttons/chrome_new.gif/images/buttons/chrome_new.gif https://fourmilab.ch/images/buttons/chrome_new.gif — 200 — 1.5 KiB — 39 ms — h2https://fourmilab.ch/images/buttons/chrome_about.gif/images/buttons/chrome_about.gif https://fourmilab.ch/images/buttons/chrome_about.gif — 200 — 1.6 KiB — 39 ms — h2https://fourmilab.ch/nav/topics.html/nav/topics.html https://fourmilab.ch/nav/topics.html — 200 — 1.1 KiB — 33 ms — h2https://fourmilab.ch/nav/topics/welcome_ch.html/nav/topics/welcome_ch.html https://fourmilab.ch/nav/topics/welcome_ch.html — 200 — 3.0 KiB — 40 ms — h2https://fourmilab.ch/nav/topics/nav.css/nav/topics/nav.css https://fourmilab.ch/nav/topics/nav.css — 200 — 0 B — 0 ms — h2https://fourmilab.ch/nav/topics/nav.css/nav/topics/nav.css https://fourmilab.ch/nav/topics/nav.css — 200 — 0 B — 0 ms — h2https://fourmilab.ch/images/icons/brave_search_64.png/images/icons/brave_search_64.png https://fourmilab.ch/images/icons/brave_search_64.png — 200 — 3.8 KiB — 34 ms — h2https://fourmilab.ch/images/bullets/ball_orange_white.gif/images/bullets/ball_orange_white.g... https://fourmilab.ch/images/bullets/ball_orange_white.gif — 200 — 863 B — 33 ms — h2https://fourmilab.ch/images/bullets/ball_blue_white.gif/images/bullets/ball_blue_white.gif https://fourmilab.ch/images/bullets/ball_blue_white.gif — 200 — 868 B — 34 ms — h2https://fourmilab.ch/favicon.ico/favicon.ico https://fourmilab.ch/favicon.ico — 200 — 865 B — 33 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 66ms · 0KB · CHF1/mo
Unattributable
Other
Optional
Execution 66ms
Transfer 0 KB
Monthly Cost CHF1/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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