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https://www.youtube.com

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
79
GRADE
C
FIX
4
REVIEW
0
PASS
8
INFO
2

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

Mobile Desktop
45
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
96
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.

942 ms

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

3.70 s

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

804 ms

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

0.028

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

3.01 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.

4.54 s

Page Load Progression

537 ms
1.1 s
1.6 s
2.1 s
2.7 s
3.2 s
3.8 s
4.3 s
Checks
14
8 PASS 4 FIX
F
Page Weight Budget
Action
3.5 MB transferred, 151 requests
FIX
3.5 MB transferred, 151 requests
Warning::
Page weighs 16.6 MB (3.5 MB transferred)
Warning::
JavaScript is 2.6 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 2.6 MB
Info::
CSS is 352 KB — consider purging unused styles
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
Got: 352 KB
Warning::
151 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.73 g CO2 per page load
3.5 MB / 2.4 MB budget
3.5 MB transferred
151 requests
0.73 g CO2 per page load
JavaScript 2.6 MiB 73%
Other 387.2 KiB 11%
CSS 352.4 KiB 10%
HTML 77.2 KiB 2%
Fonts 68.1 KiB 2%
Other 36.4 KiB 1%
Other 25.8 KiB 1%
Other 1.9 KiB 0%
Other 288 B 0%
Images 76 B 0%
0 2.4 MB 4.9 MB
Over budget

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

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

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
3477ms total JS execution
FIX
3477ms total JS execution
Warning::
https://www.youtube.com/s/_/ytmainappweb/_/js/k=yt...: 1833ms CPU time
Warning::
Unattributable: 577ms CPU time
Warning::
https://www.youtube.com/s/desktop/0203efec/jsbin/w...: 535ms CPU time
Warning::
https://www.youtube.com/s/player/57fefa84/player_e...: 289ms CPU time
Info::
https://www.youtube.com/: 243ms CPU time
Info::
Third-party scripts: 577ms (17% of total)

Main Thread Breakdown

Script Evaluation 66% Other 13% Script Parsing & Compilation 9% Style & Layout 5% Parse HTML & CSS 4%
ScriptTotalScriptingParse/CompileParty
https://www.youtube.com/s/_/ytmainappweb/_/js/k=ytmainappweb.kevlar_base.en_US.zRTiNATFin8.es5.O/am=AAAAAgAAIAE/d=1/br=1/rs=AGKMywHgEkn2QsaXPRgwZ5kiaKEgDzy-mQ/m=kevlar_base_module,kevlar_main_module1833ms1383ms256ms1st
Unattributable577ms167ms0ms3rd
https://www.youtube.com/s/desktop/0203efec/jsbin/web-animations-next-lite.min.vflset/web-animations-next-lite.min.js535ms426ms1ms1st
https://www.youtube.com/s/player/57fefa84/player_es6.vflset/en_US/base.js289ms195ms73ms1st
https://www.youtube.com/243ms22ms24ms1st
F
JS Bundles
Action
19 scripts, 1.6 MB unused
FIX
19 scripts, 1.6 MB unused
Warning::
https://www.youtube.com/s/_/ytmainappweb/_/js/k=yt...: 1.1 MB unused (61%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.youtube.com/s/player/57fefa84/player_e...: 475 KB unused (74%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.youtube.com/s/player/57fefa84/player_e...: 27 KB unused (78%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 1.6 MB
1619 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.youtube.com/s/_/ytmainappweb/_/js/k=ytmainappweb.kevlar_base.en_US.zRTiNATFin8.es5.O/am=AAAAAgAAIAE/d=1/br=1/rs=AGKMywHgEkn2QsaXPRgwZ5kiaKEgDzy-mQ/m=kevlar_base_module,kevlar_main_module1832 KB1117 KB (61%)✓1st
https://www.youtube.com/s/player/57fefa84/player_es6.vflset/en_US/base.js638 KB475 KB (74%)✓1st
https://www.youtube.com/s/player/57fefa84/player_es6.vflset/en_US/remote.js34 KB27 KB (78%)✓1st
https://www.youtube.com/s/desktop/0203efec/jsbin/intersection-observer.min.vflset/intersection-observer.min.js2 KB—✓1st
https://www.youtube.com/s/desktop/0203efec/jsbin/custom-elements-es5-adapter.vflset/custom-elements-es5-adapter.js1 KB—✓1st
https://www.youtube.com/s/desktop/0203efec/jsbin/scheduler.vflset/scheduler.js3 KB—✓1st
https://www.youtube.com/s/desktop/0203efec/jsbin/www-i18n-constants-en_US.vflset/www-i18n-constants.js2 KB—✓1st
https://www.youtube.com/s/desktop/0203efec/jsbin/spf.vflset/spf.js12 KB—✓1st
https://www.youtube.com/s/desktop/0203efec/jsbin/network.vflset/network.js5 KB—✓1st
https://www.google.com/js/th/PF32M1WFt3Opj6X4HHxBvSVo4hj3YoJbcs9XKKWIAD0.js23 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

D
HTTP Caching
Action
no-store (uncacheable)
FIX
no-store (uncacheable)
Info::
Cache-Control: no-store prevents all caching
Intentional for dynamic content, but increases server load for every page view.
Got: no-cache, no-store, max-age=0, must-revalidate
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

no-cache, no-store, max-age=0, must-revalidate

DirectiveValueMeaning
no-cache—Cache but always revalidate first
no-store—Never cache this response
max-age0Cache for 0 seconds
must-revalidate—Must recheck with server after expiry
A+
Third-Party Impact
15% third-party, 0 ms blocking
PASS
15% third-party, 0 ms blocking
Info::
Third-party code accounts for 15% of page weight (542.4 KiB of 3.5 MiB)
Info::
Third-party blocking time is low (0 ms)
85%
15%
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
Image Optimization
2 images, 0 KB saveable
PASS
2 images, 0 KB saveable
Info::
All images are well-optimized
2 images 0 KB
0 oversized -0 KB
2 legacy format
0 missing dimensions CLS risk
A+
Font Loading
2 fonts (68 KB)
PASS
2 fonts (68 KB)
Info::
2 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

2

68 KB total

Render-blocking

0

of 2

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 1.0 s 2.0 s 3.0 s FCP 942 ms LCP 3.7 shttps://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 36.7 KiB — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/youtubesans/v32/Qw38ZQNGEDjaO2m6tqIqX5E-AVS5_rSejo46_PCTRspJ0OosolrBEJL3HO_T7fHoCVHx.woff2Qw38ZQNGEDjaO2m6tqIqX5E... https://fonts.gstatic.com/s/youtubesans/v32/Qw38ZQNGEDjaO2m6tqIqX5E-AVS5_rSejo46_PCTRspJ0OosolrBEJL3HO_T7fHoCVHx.woff2 — 31.5 KiB — 0 ms — font-display: swap
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 37 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
Qw38ZQNGEDjaO2m6tqIqX5E... woff2 swap
Size 31 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)
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+
Green Hosting
Whether the site is served from green-energy infrastructure
PASS

Green Hosting

This site is hosted on green energy infrastructure

Provider: Google Cloud

Network Waterfall
151 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
17% of JavaScript execution is third-party
First-party Third-party 577ms · 0KB · $8/mo
Unattributable
Other
Costly
Execution 577ms
Transfer 0 KB
Monthly Cost $8/mo

These scripts may cost more than they're worth

  • Unattributable adds 577ms and costs ~$8/month

Unattributable takes 577ms 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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