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https://www.ethz.ch

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
71
GRADE
C
FIX
4
REVIEW
3
PASS
5
INFO
2

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

Mobile Desktop
41
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
95
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.
83
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.

1.86 s

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

2.65 s

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

225 ms

Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.

0.702

Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.

2.73 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.

2.65 s

Page Load Progression

463 ms
927 ms
1.4 s
1.9 s
2.3 s
2.8 s
3.2 s
3.7 s
Checks
14
5 PASS 3 REVIEW 4 FIX
F
Page Weight Budget
Action
4.6 MB transferred, 50 requests
FIX
4.6 MB transferred, 50 requests
Critical::
Page weighs 10.2 MB (4.6 MB transferred)
Warning::
Images are 2.9 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 2.9 MB
Warning::
JavaScript is 1.2 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.2 MB
Info::
Fonts are 219 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 219 KB
Info::
50 HTTP requests
Info::
Estimated 0.96 g CO2 per page load
4.6 MB / 2.4 MB budget
4.6 MB transferred
50 requests
0.96 g CO2 per page load
Images 2.9 MiB 63%
JavaScript 1.2 MiB 27%
Fonts 219.4 KiB 5%
CSS 81.7 KiB 2%
Other 75.6 KiB 2%
Other 67.0 KiB 1%
HTML 15.6 KiB 0%
Other 3.3 KiB 0%
0 2.4 MB 4.9 MB
Over budget

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

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

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 (4.6 MiB of 4.6 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Bundles
Action
4 scripts, 541 KB unused
FIX
4 scripts, 541 KB unused
Warning::
https://ethz.ch/etc/designs/ethz/js/default.js: 406 KB unused (42%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-5KC...: 69 KB unused (39%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://cdn.cookielaw.org/scripttemplates/202511.1...: 66 KB unused (53%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 541 KB
541 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://ethz.ch/etc/designs/ethz/js/default.js960 KB406 KB (42%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-5KC3PX6176 KB69 KB (39%)✓3rd
https://cdn.cookielaw.org/scripttemplates/202511.1.0/otBannerSdk.js124 KB66 KB (53%)✓3rd
https://cdn.cookielaw.org/scripttemplates/otSDKStub.js?did=d4b64b56-c565-41a3-9aef-2523cd72f471&data-document-language=true9 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

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
26 images, 0 KB saveable
REVIEW
26 images, 0 KB saveable
Warning::
https://ethz.ch/de/news-und-veranstaltungen/eth-ne... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://ethz.ch/de/news-und-veranstaltungen/eth-ne... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://ethz.ch/etc/designs/ethz/img/icons/svg/lin... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://ethz.ch/etc/designs/ethz/img/icons/svg/you... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://ethz.ch/etc/designs/ethz/img/icons/svg/rss... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://ethz.ch/etc/designs/ethz/img/icons/svg/ins... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://ethz.ch/etc/designs/ethz/img/icons/svg/tik... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://ethz.ch/etc/designs/ethz/img/icons/svg/fac... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
26 images 2.9 MB
0 oversized -0 KB
23 legacy format
9 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

Set explicit width and height to prevent CLS.

Why this matters

Performance issues directly impact user engagement and conversion rates.

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

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

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
JS Execution Cost
Action
1354ms total JS execution
REVIEW
1354ms total JS execution
Warning::
https://ethz.ch/etc/designs/ethz/js/default.js: 732ms CPU time
Warning::
https://ethz.ch/de.html: 254ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-5KC...: 149ms CPU time
Info::
Unattributable: 127ms CPU time
Info::
https://cdn.cookielaw.org/scripttemplates/202511.1...: 91ms CPU time
Warning::
Third-party scripts: 1354ms (100% of total)

Main Thread Breakdown

Script Evaluation 44% Other 21% Script Parsing & Compilation 13% Style & Layout 12% Parse HTML & CSS 7%
ScriptTotalScriptingParse/CompileParty
https://ethz.ch/etc/designs/ethz/js/default.js732ms415ms136ms3rd
https://ethz.ch/de.html254ms14ms1ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-5KC3PX6149ms125ms20ms3rd
Unattributable127ms3ms0ms3rd
https://cdn.cookielaw.org/scripttemplates/202511.1.0/otBannerSdk.js91ms49ms15ms3rd
C
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
Info::
All text resources are compressed
All text resources are properly compressed.
A+
Font Loading
4 fonts (219 KB)
PASS
4 fonts (219 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

219 KB total

Render-blocking

0

of 4

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 2.5 s FCP 1.9 s LCP 2.7 shttps://ethz.ch/bin/ethz/fonts/regular.woff2regular.woff2 https://ethz.ch/bin/ethz/fonts/regular.woff2 — 32.9 KiB — 0 ms — font-display: swaphttps://ethz.ch/bin/ethz/fonts/bold.woff2bold.woff2 https://ethz.ch/bin/ethz/fonts/bold.woff2 — 26.2 KiB — 0 ms — font-display: swaphttps://ethz.ch/bin/ethz/fonts/medium.woff2medium.woff2 https://ethz.ch/bin/ethz/fonts/medium.woff2 — 32.8 KiB — 0 ms — font-display: swaphttps://ethz.ch/etc/designs/ethz/fonts/MaterialIcons-Outlined.woff2MaterialIcons-Outlined.... https://ethz.ch/etc/designs/ethz/fonts/MaterialIcons-Outlined.woff2 — 127.5 KiB — 0 ms — font-display: swap
regular.woff2 woff2 swap
Size 33 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
bold.woff2 woff2 swap
Size 26 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
medium.woff2 woff2 swap
Size 33 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
MaterialIcons-Outlined.... woff2 swap
Size 127 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
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 ~64 KB and ~128 ms

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
Network Waterfall
50 requests over 0ms
INFO

Performance analysis not available for this result.

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 1354ms · 1276KB · CHF21/mo
ethz.ch
Other
Costly
Execution 732ms
Transfer 960 KB
Unused 42%
Monthly Cost CHF12/mo
ethz.ch
Other
Costly
Execution 254ms
Transfer 16 KB
Monthly Cost CHF4/mo
Google Tag Manager
Tag Manager
Optional
Execution 149ms
Transfer 176 KB
Unused 39%
Monthly Cost CHF2/mo
Unattributable
Other
Optional
Execution 127ms
Transfer 0 KB
Monthly Cost CHF2/mo
OneTrust
Consent
Essential
Execution 91ms
Transfer 124 KB
Unused 53%
Monthly Cost CHF1/mo

These scripts may cost more than they're worth

  • ethz.ch adds 732ms and costs ~CHF12/month
  • ethz.ch adds 254ms and costs ~CHF4/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

ethz.ch takes 732ms 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

ethz.ch takes 254ms 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

53% of OneTrust'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

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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