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Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
79
GRADE
C
FIX
2
REVIEW
3
PASS
9
INFO
2

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

Mobile Desktop
51
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
84
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.
100
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.

12.96 s

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

19.98 s

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

148 ms

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

0.094

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

12.96 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.

20.37 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
16
9 PASS 3 REVIEW 2 FIX
F
Page Weight Budget
Action
5.0 MB transferred, 64 requests
FIX
5.0 MB transferred, 64 requests
Critical::
Page weighs 5.2 MB (5.0 MB transferred)
Warning::
Images are 2.7 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 2.7 MB
Info::
Fonts are 761 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 761 KB
Info::
CSS is 719 KB — consider purging unused styles
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
Got: 719 KB
Warning::
JavaScript is 625 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 625 KB
Info::
64 HTTP requests
Info::
Estimated 1.1 g CO2 per page load
5.0 MB / 2.4 MB budget
5.0 MB transferred
64 requests
1.1 g CO2 per page load
Images 2.7 MiB 54%
Fonts 760.7 KiB 15%
CSS 719.1 KiB 14%
JavaScript 624.7 KiB 12%
HTML 239.0 KiB 5%
Other 15.4 KiB 0%
Other 266 B 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

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

Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.

Why this matters

CSS bundle is large — purge unused styles (PurgeCSS, Tailwind JIT) to reduce CSS payload.

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
10 scripts, 328 KB unused
FIX
10 scripts, 328 KB unused
Warning::
https://www.polytechnique.edu/modules/custom/nc_pr...: 192 KB unused (74%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.polytechnique.edu/modules/custom/nc_pr...: unminified — 70 KB could be saved
Warning::
https://www.polytechnique.edu/sites/default/files/...: 99 KB unused (43%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://stats-web.polytechnique.fr/piwik.js: 37 KB unused (56%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 328 KB
328 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.polytechnique.edu/modules/custom/nc_project/libraries/tarteaucitron/tarteaucitron.services.js261 KB192 KB (74%)✗1st
https://www.polytechnique.edu/sites/default/files/js/js_OZmef4KJtRVchQD0OTwkGGzdxF9Xs9VJaRG-GXcWnf4.js?scope=footer&delta=0&language=fr&theme=project&include=eJzLS45PTcksyS_Sz4Ox9NKK8vNKdAqK8rNSk0v003PykxJzdItLKnMy89IBzsIS7w230 KB99 KB (43%)✓1st
https://stats-web.polytechnique.fr/piwik.js67 KB37 KB (56%)✓3rd
https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js7 KB—✓3rd
https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js16 KB—✓3rd
https://cdn.jsdelivr.net/npm/select2@4.1.0-rc.0/dist/js/select2.min.js18 KB—✓3rd
https://cdn.jsdelivr.net/npm/slick-carousel@1.8.1/slick/slick.min.js11 KB—✓3rd
https://cdnjs.cloudflare.com/ajax/libs/slick-lightbox/0.2.12/slick-lightbox.min.js2 KB—✓3rd
https://www.polytechnique.edu/sites/default/files/js/js_9QyOVXYMijwNRJKi_86pNrLU97XFO4x7LzDQVN_sE-U.js?scope=footer&delta=6&language=fr&theme=project&include=eJzLS45PTcksyS_Sz4Ox9NKK8vNKdAqK8rNSk0v003PykxJzdItLKnMy89IBzsIS7w8 KB—✓1st
https://www.polytechnique.edu/modules/custom/nc_project/libraries/tarteaucitron/lang/tarteaucitron.fr.js5 KB—✓1st

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

C
Image Optimization
Action
29 images, 0 KB saveable
REVIEW
29 images, 0 KB saveable
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.polytechnique.edu/sites/default/files/... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
29 images 2.7 MB
0 oversized -0 KB
26 legacy format
11 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

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

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
1406ms total JS execution
REVIEW
1406ms total JS execution
Warning::
https://www.polytechnique.edu/sites/default/files/...: 546ms CPU time
Warning::
https://www.polytechnique.edu/: 544ms CPU time
Warning::
Unattributable: 315ms CPU time
Info::
Third-party scripts: 315ms (22% of total)

Main Thread Breakdown

Other 38% Style & Layout 25% Script Evaluation 24% Parse HTML & CSS 7% Script Parsing & Compilation 5%
ScriptTotalScriptingParse/CompileParty
https://www.polytechnique.edu/sites/default/files/js/js_OZmef4KJtRVchQD0OTwkGGzdxF9Xs9VJaRG-GXcWnf4.js?scope=footer&delta=0&language=fr&theme=project&include=eJzLS45PTcksyS_Sz4Ox9NKK8vNKdAqK8rNSk0v003PykxJzdItLKnMy89IBzsIS7w546ms291ms20ms1st
https://www.polytechnique.edu/544ms19ms2ms1st
Unattributable315ms10ms0ms3rd
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Third-Party Impact
6% third-party, 0 ms blocking
PASS
6% third-party, 0 ms blocking
Info::
Third-party code accounts for 6% of page weight (319.5 KiB of 5.0 MiB)
Info::
Third-party blocking time is low (0 ms)
94%
First-party Third-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+
Font Loading
10 fonts (761 KB)
PASS
10 fonts (761 KB)
Info::
10 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

10

761 KB total

Render-blocking

0

of 10

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 14.0 s 16.0 s 18.0 s 20.0 s FCP 13.0 s LCP 20.0 shttps://fonts.gstatic.com/s/barlow/v13/7cHpv4kjgoGqM7E_DMs5ynghnQ.woff27cHpv4kjgoGqM7E_DMs5yng... https://fonts.gstatic.com/s/barlow/v13/7cHpv4kjgoGqM7E_DMs5ynghnQ.woff2 — 15.3 KiB — 0 ms — font-display: swaphttps://www.polytechnique.edu/themes/project/css/webfonts/fa-light-300.woff2fa-light-300.woff2 https://www.polytechnique.edu/themes/project/css/webfonts/fa-light-300.woff2 — 455.2 KiB — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3q-0s51ostz0rdg.woff27cHqv4kjgoGqM7E3q-0s51o... https://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3q-0s51ostz0rdg.woff2 — 15.3 KiB — 0 ms — font-display: swaphttps://use.typekit.net/af/af619f/00000000000000003b9b00c5/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3l https://use.typekit.net/af/af619f/00000000000000003b9b00c5/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3 — 36.4 KiB — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3t-4s51ostz0rdg.woff27cHqv4kjgoGqM7E3t-4s51o... https://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3t-4s51ostz0rdg.woff2 — 15.4 KiB — 0 ms — font-display: swaphttps://use.typekit.net/af/2011b6/00000000000000003b9b00c1/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/2011b6/00000000000000003b9b00c1/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 59.8 KiB — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3_-gs51ostz0rdg.woff27cHqv4kjgoGqM7E3_-gs51o... https://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3_-gs51ostz0rdg.woff2 — 15.3 KiB — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E30-8s51ostz0rdg.woff27cHqv4kjgoGqM7E30-8s51o... https://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E30-8s51ostz0rdg.woff2 — 15.5 KiB — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3p-ks51ostz0rdg.woff27cHqv4kjgoGqM7E3p-ks51o... https://fonts.gstatic.com/s/barlow/v13/7cHqv4kjgoGqM7E3p-ks51ostz0rdg.woff2 — 15.2 KiB — 0 ms — font-display: swaphttps://www.polytechnique.edu/themes/project/css/webfonts/fa-brands-400.woff2fa-brands-400.woff2 https://www.polytechnique.edu/themes/project/css/webfonts/fa-brands-400.woff2 — 117.2 KiB — 0 ms — font-display: swap
7cHpv4kjgoGqM7E_DMs5yng... woff2 swap
Size 15 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
fa-light-300.woff2 woff2 swap
Size 455 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
7cHqv4kjgoGqM7E3q-0s51o... woff2 swap
Size 15 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 36 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
7cHqv4kjgoGqM7E3t-4s51o... woff2 swap
Size 15 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 60 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
7cHqv4kjgoGqM7E3_-gs51o... woff2 swap
Size 15 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
7cHqv4kjgoGqM7E30-8s51o... woff2 swap
Size 15 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
7cHqv4kjgoGqM7E3p-ks51o... woff2 swap
Size 15 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
fa-brands-400.woff2 woff2 swap
Size 117 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 ~286 KB and ~572 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
A+
HTTP Caching
max-age=86400 (1 day)
PASS
max-age=86400 (1 day)
Info::
Cache-Control header is set
Got: max-age=86400, public
Info::
Effective TTL: 1 day (max-age=86400)
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present
Cache-Control

max-age=86400, public

DirectiveValueMeaning
max-age86400Cache for 1 day
public—Any cache may store this response
Effective TTL: 86400 seconds
Network Waterfall
64 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
22% of JavaScript execution is third-party
First-party Third-party 315ms · 0KB · €3/mo
Unattributable
Other
Costly
Execution 315ms
Transfer 0 KB
Monthly Cost €3/mo

These scripts may cost more than they're worth

  • Unattributable adds 315ms and costs ~€3/month

Unattributable takes 315ms 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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