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https://www.janestreet.com

Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
74
GRADE
C
FIX
3
REVIEW
4
PASS
7
INFO
2

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

Mobile Desktop
50
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
81
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.
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.

6.05 s

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

39.66 s

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

316 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.

8.65 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.

41.95 s

Page Load Progression

598 ms
1.2 s
1.8 s
2.4 s
3.0 s
3.6 s
4.2 s
4.8 s
Checks
16
7 PASS 4 REVIEW 3 FIX
F
Page Weight Budget
Action
20.4 MB transferred, 113 requests
FIX
20.4 MB transferred, 113 requests
Critical::
Page weighs 27.3 MB (20.4 MB transferred)
Warning::
Images are 12.1 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 12.1 MB
Warning::
JavaScript is 1.3 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.3 MB
Info::
Fonts are 688 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 688 KB
Warning::
113 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 4.3 g CO2 per page load
20.4 MB / 2.4 MB budget
20.4 MB transferred
113 requests
4.3 g CO2 per page load
Images 12.1 MiB 59%
Other 6.3 MiB 31%
JavaScript 1.3 MiB 6%
Fonts 687.7 KiB 3%
HTML 18.7 KiB 0%
CSS 16.5 KiB 0%
Other 11.4 KiB 0%
Other 1.7 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

Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.

Why this matters

High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.

Source: web.dev

D
JS Execution Cost
Action
3376ms total JS execution
FIX
3376ms total JS execution
Warning::
https://fast.wistia.net/assets/external/E-v1.js: 980ms CPU time
Warning::
Unattributable: 743ms CPU time
Warning::
https://www.janestreet.com/assets/main-6772b671989...: 430ms CPU time
Warning::
https://www.googletagmanager.com/gtag/js?id=G-1R7Q...: 323ms CPU time
Info::
https://fast.wistia.net/assets/external/iframeApi....: 218ms CPU time
Warning::
Third-party scripts: 2544ms (75% of total)

Main Thread Breakdown

Script Evaluation 50% Other 28% Script Parsing & Compilation 15% Style & Layout 3%
ScriptTotalScriptingParse/CompileParty
https://fast.wistia.net/assets/external/E-v1.js980ms646ms276ms3rd
Unattributable743ms40ms0ms3rd
https://www.janestreet.com/assets/main-6772b6719891e16e3ae77c74c5f08294832adfc669521670fc32f5df16e865a0.js430ms262ms41ms1st
https://www.googletagmanager.com/gtag/js?id=G-1R7QL7MQRB323ms257ms64ms3rd
https://fast.wistia.net/assets/external/iframeApi.js@49b80af9d2806884c566f240cb7a5b25caa013f7218ms131ms1ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-KCHZL5R185ms148ms36ms3rd
https://www.janestreet.com/assets/vendor/gsapScrollTrigger.min-64b12f49d4fad45cdb1787545de4120518327301825f3b8d7b335d125e4195a8.js143ms60ms3ms1st
https://www.janestreet.com/101ms24ms4ms1st
https://www.janestreet.com/assets/vendor/gsap.min-0f005b992d31aa7fea9ae6f3bc1188c6fb8a953eb4dbeae7f0a34c818c3386c5.js98ms40ms7ms1st
https://www.googletagmanager.com/gtag/js?id=G-1R7QL7MQRB&cx=c&gtm=4e646095ms32ms62ms3rd

Showing top 10 of 11 scripts

F
JS Bundles
Action
29 scripts, 687 KB unused
FIX
29 scripts, 687 KB unused
Warning::
https://fast.wistia.net/assets/external/E-v1.js: 120 KB unused (74%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://fast.wistia.net/assets/external/E-v1.js: 120 KB unused (74%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://fast.wistia.net/assets/external/E-v1.js: 120 KB unused (74%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=G-1R7Q...: 115 KB unused (65%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.janestreet.com/assets/main-6772b671989...: 78 KB unused (69%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 687 KB
687 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://fast.wistia.net/assets/external/E-v1.js162 KB120 KB (74%)✓3rd
https://fast.wistia.net/assets/external/E-v1.js0 KB120 KB (74%)✓3rd
https://fast.wistia.net/assets/external/E-v1.js162 KB120 KB (74%)✓3rd
https://www.googletagmanager.com/gtag/js?id=G-1R7QL7MQRB&cx=c&gtm=4e6460175 KB115 KB (65%)✓3rd
https://www.janestreet.com/assets/main-6772b6719891e16e3ae77c74c5f08294832adfc669521670fc32f5df16e865a0.js114 KB78 KB (69%)✓1st
https://www.googletagmanager.com/gtag/js?id=G-1R7QL7MQRB175 KB71 KB (40%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-KCHZL5R124 KB64 KB (52%)✓3rd
https://www.janestreet.com/assets/components/v4-carousel-030b2654000f6ac3a49b8e930cffb84a4fbb998d15261b98787a73d416b8fcff.js2 KB—✓1st
https://fast.wistia.net/assets/external/insideIframe.js@49b80af9d2806884c566f240cb7a5b25caa013f724 KB—✓3rd
https://www.janestreet.com/assets/pg/the-latest-7f5a2eeb938761aad9b2f815ad586714dddd32c7218f12957c04f0d30227cf1b.js4 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

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

B
Third-Party Impact
58% third-party, 0 ms blocking
REVIEW
58% third-party, 0 ms blocking
Warning::
Third-party code accounts for 58% of page weight (11.8 MiB of 20.4 MiB)
Info::
Third-party blocking time is low (0 ms)
42%
58%
First-party Third-party
C
Image Optimization
Action
37 images, 0 KB saveable
REVIEW
37 images, 0 KB saveable
Warning::
https://www.janestreet.com/assets/logo_horizontal-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.janestreet.com/assets/icon-menu-c17044... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
37 images 12.1 MB
0 oversized -0 KB
36 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

B
HTTP Caching
no-cache
REVIEW
no-cache
Info::
Cache-Control header is set
Got: no-cache
Info::
Last-Modified header present
Cache-Control

no-cache

DirectiveValueMeaning
no-cache—Cache but always revalidate first
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
5 fonts (688 KB)
PASS
5 fonts (688 KB)
Info::
5 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

5

688 KB total

Render-blocking

0

of 5

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 22.0 s 24.0 s 26.0 s 28.0 s 30.0 s 32.0 s 34.0 s 36.0 s 38.0 s 40.0 s FCP 6.0 s LCP 39.7 shttps://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Light-1v7.otfAlrightSansLT-Light-1v7... https://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Light-1v7.otf — 136.2 KiB — 0 ms — font-display: swaphttps://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Medium-1v7.otfAlrightSansLT-Medium-1v... https://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Medium-1v7.otf — 136.6 KiB — 0 ms — font-display: swaphttps://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Black-1v7.otfAlrightSansLT-Black-1v7... https://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Black-1v7.otf — 139.7 KiB — 0 ms — font-display: swaphttps://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Regular-1v7.otfAlrightSansLT-Regular-1... https://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-Regular-1v7.otf — 135.5 KiB — 0 ms — font-display: swaphttps://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-LightItalic-1v7.otfAlrightSansLT-LightItal... https://www.janestreet.com/static/fonts/Alright-Sans-LT/AlrightSansLT-LightItalic-1v7.otf — 139.8 KiB — 0 ms — font-display: swap
AlrightSansLT-Light-1v7... otf swap
Size 136 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
AlrightSansLT-Medium-1v... otf swap
Size 137 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
AlrightSansLT-Black-1v7... otf swap
Size 140 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
AlrightSansLT-Regular-1... otf swap
Size 135 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
AlrightSansLT-LightItal... otf swap
Size 140 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • 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 ~550 KB and ~1100 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
4 hints, 0 missing preconnects
PASS
4 hints, 0 missing preconnects
Info::
Page uses 4 resource hint(s)

Current Resource Hints

preconnect
—
preload
4
dns-prefetch
—
prefetch
—

4 resource hints configured

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
113 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
75% of JavaScript execution is third-party
First-party Third-party 2544ms · 504KB · €28/mo
fast.wistia.net
Other
Costly
Execution 980ms
Transfer 0 KB
Unused 74%
Monthly Cost €11/mo
Unattributable
Other
Costly
Execution 743ms
Transfer 0 KB
Monthly Cost €8/mo
Google Tag Manager
Tag Manager
Costly
Execution 323ms
Transfer 175 KB
Unused 40%
Monthly Cost €4/mo
fast.wistia.net
Other
Costly
Execution 218ms
Transfer 30 KB
Monthly Cost €2/mo
Google Tag Manager
Tag Manager
Optional
Execution 185ms
Transfer 124 KB
Unused 52%
Monthly Cost €2/mo
Google Tag Manager
Tag Manager
Optional
Execution 95ms
Transfer 175 KB
Unused 65%
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • fast.wistia.net adds 980ms and costs ~€11/month
  • Unattributable adds 743ms and costs ~€8/month
  • Google Tag Manager adds 323ms and costs ~€4/month
  • fast.wistia.net adds 218ms and costs ~€2/month

75% 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

fast.wistia.net takes 980ms 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

74% of fast.wistia.net'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

Unattributable takes 743ms 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 323ms 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

fast.wistia.net takes 218ms 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

52% of Google Tag Manager'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

65% of Google Tag Manager'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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