Skip to content
https://www.ethz.ch

Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
71
GRADE
C
FIX
5
REVIEW
2
PASS
7
INFO
2

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

Mobile Desktop
20
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.
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.

8.79 s

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

12.38 s

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

2.05 s

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

0.192

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

8.79 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.

13.90 s

Page Load Progression

441 ms
881 ms
1.3 s
1.8 s
2.2 s
2.6 s
3.1 s
3.5 s
Checks
16
7 PASS 2 REVIEW 5 FIX
F
Page Weight Budget
Action
3.6 MB transferred, 43 requests
FIX
3.6 MB transferred, 43 requests
Warning::
Page weighs 9.3 MB (3.6 MB transferred)
Warning::
Images are 2.0 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 2.0 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::
43 HTTP requests
Info::
Estimated 0.77 g CO2 per page load
3.6 MB / 2.4 MB budget
3.6 MB transferred
43 requests
0.77 g CO2 per page load
Images 2.0 MiB 54%
JavaScript 1.2 MiB 34%
Fonts 219.4 KiB 6%
CSS 81.7 KiB 2%
Other 75.6 KiB 2%
Other 67.0 KiB 2%
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 (3.6 MiB of 3.6 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Execution Cost
Action
4408ms total JS execution
FIX
4408ms total JS execution
Warning::
https://ethz.ch/etc/designs/ethz/js/default.js: 2218ms CPU time
Warning::
https://ethz.ch/de.html: 863ms CPU time
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-5KC...: 593ms CPU time
Warning::
Unattributable: 377ms CPU time
Warning::
https://cdn.cookielaw.org/scripttemplates/202511.1...: 293ms CPU time
Warning::
Third-party scripts: 4408ms (100% of total)

Main Thread Breakdown

Script Evaluation 49% Other 17% Script Parsing & Compilation 16% Style & Layout 12% Parse HTML & CSS 3%
ScriptTotalScriptingParse/CompileParty
https://ethz.ch/etc/designs/ethz/js/default.js2218ms1421ms546ms3rd
https://ethz.ch/de.html863ms52ms5ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-5KC3PX6593ms497ms82ms3rd
Unattributable377ms11ms0ms3rd
https://cdn.cookielaw.org/scripttemplates/202511.1.0/otBannerSdk.js293ms178ms60ms3rd
https://ethz.ch/etc/designs/ethz/css.css64ms0ms0ms3rd
F
JS Bundles
Action
4 scripts, 540 KB unused
FIX
4 scripts, 540 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: 540 KB
540 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
19 images, 0 KB saveable
REVIEW
19 images, 0 KB saveable
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/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/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/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/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.
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.
19 images 2.0 MB
0 oversized -0 KB
17 legacy format
8 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

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 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s FCP 8.8 s LCP 12.4 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/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: 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: swap
regular.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
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
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
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
43 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 4408ms · 1357KB · CHF70/mo
ethz.ch
Other
Costly
Execution 2218ms
Transfer 960 KB
Unused 42%
Monthly Cost CHF35/mo
ethz.ch
Other
Costly
Execution 863ms
Transfer 16 KB
Monthly Cost CHF14/mo
Google Tag Manager
Tag Manager
Costly
Execution 593ms
Transfer 176 KB
Unused 39%
Monthly Cost CHF9/mo
Unattributable
Other
Costly
Execution 377ms
Transfer 0 KB
Monthly Cost CHF6/mo
OneTrust
Consent
Essential
Execution 293ms
Transfer 124 KB
Unused 53%
Monthly Cost CHF5/mo
ethz.ch
Other
Optional
Execution 64ms
Transfer 82 KB
Monthly Cost CHF1/mo

These scripts may cost more than they're worth

  • ethz.ch adds 2218ms and costs ~CHF35/month
  • ethz.ch adds 863ms and costs ~CHF14/month
  • Google Tag Manager adds 593ms and costs ~CHF9/month
  • Unattributable adds 377ms and costs ~CHF6/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 2218ms 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 863ms 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

Google Tag Manager takes 593ms 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

Unattributable takes 377ms 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.

Send Feedback