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Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
74
GRADE
C
FIX
4
REVIEW
3
PASS
5
INFO
2

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

Mobile Desktop
78
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
100
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.

1.52 s

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

2.37 s

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

120 ms

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

0.010

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

1.81 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.

2.43 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
14
5 PASS 3 REVIEW 4 FIX
F
Page Weight Budget
Action
3.2 MB transferred, 122 requests
FIX
3.2 MB transferred, 122 requests
Warning::
Page weighs 5.8 MB (3.2 MB transferred)
Warning::
Images are 1.8 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 1.8 MB
Warning::
JavaScript is 1.1 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.1 MB
Warning::
122 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.67 g CO2 per page load
3.2 MB / 2.4 MB budget
3.2 MB transferred
122 requests
0.67 g CO2 per page load
Images 1.8 MiB 56%
JavaScript 1.1 MiB 33%
Fonts 163.5 KiB 5%
Other 102.7 KiB 3%
HTML 59.4 KiB 2%
CSS 10.3 KiB 0%
Other 1.6 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

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
Third-Party Impact
Action
96% third-party, 0 ms blocking
FIX
96% third-party, 0 ms blocking
Warning::
Third-party code accounts for 96% of page weight (3.1 MiB of 3.2 MiB)
Info::
Third-party blocking time is low (0 ms)
96%
First-party Third-party
F
JS Bundles
Action
29 scripts, 508 KB unused
FIX
29 scripts, 508 KB unused
Warning::
https://cdn.kastatic.org/khanacademy/khanacademy.d...: 396 KB unused (56%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-WSX...: 87 KB unused (58%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://cdn.kastatic.org/khanacademy/36639.dbefd49...: 25 KB unused (75%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 508 KB
508 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://cdn.kastatic.org/khanacademy/khanacademy.d010d00049edb0e5.js716 KB396 KB (56%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-WSX5PBP151 KB87 KB (58%)✓3rd
https://cdn.kastatic.org/khanacademy/36639.dbefd49b0f07f21d.js34 KB25 KB (75%)✓3rd
https://cdn.kastatic.org/khanacademy/31495.0eef11fe1527dfee.js3 KB—✓3rd
https://cdn.kastatic.org/khanacademy/71178.288b55000ec490ce.js5 KB—✓3rd
https://cdn.kastatic.org/khanacademy/68372.c7bc1a7eb023bfa4.js2 KB—✓3rd
https://cdn.kastatic.org/khanacademy/70737.3a6c14f50b43236a.js3 KB—✓3rd
https://cdn.kastatic.org/khanacademy/62312.8c8cbea21f270da4.js2 KB—✓3rd
https://cdn.kastatic.org/khanacademy/73950.aabeead257a16f5d.js5 KB—✓3rd
https://cdn.kastatic.org/khanacademy/47596.f92b1d759e13891b.js24 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: private, no-store
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

private, no-store

DirectiveValueMeaning
private—Only browser cache, not CDN/proxy
no-store—Never cache this response
C
Image Optimization
Action
56 images, 0 KB saveable
REVIEW
56 images, 0 KB saveable
Warning::
https://cdn.kastatic.org/images/lohp/laptop_collag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/store-badges/googl... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/lohp/boost-scores.... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/lohp/faces_collage... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/lohp/math-unicorn-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/lohp/anjali-3.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/lohp/personalized_... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/lohp/empower_teach... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://tools.applemediaservices.com/api/badges/do... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cdn.kastatic.org/images/lohp/trusted_conte... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
56 images 1.8 MB
0 oversized -0 KB
54 legacy format
10 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

C
JS Execution Cost
Action
1258ms total JS execution
REVIEW
1258ms total JS execution
Warning::
https://cdn.kastatic.org/khanacademy/khanacademy.d...: 655ms CPU time
Info::
Unattributable: 206ms CPU time
Info::
https://www.khanacademy.org/: 191ms CPU time
Info::
https://cdn.kastatic.org/khanacademy/62538.dff4252...: 152ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-WSX...: 54ms CPU time
Warning::
Third-party scripts: 1067ms (85% of total)

Main Thread Breakdown

Script Evaluation 55% Other 20% Style & Layout 12% Script Parsing & Compilation 9% Rendering 3%
ScriptTotalScriptingParse/CompileParty
https://cdn.kastatic.org/khanacademy/khanacademy.d010d00049edb0e5.js655ms495ms65ms3rd
Unattributable206ms20ms0ms3rd
https://www.khanacademy.org/191ms10ms21ms1st
https://cdn.kastatic.org/khanacademy/62538.dff4252417408d47.js152ms124ms2ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-WSX5PBP54ms40ms14ms3rd
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
5 fonts (163 KB)
PASS
5 fonts (163 KB)
Info::
5 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

5

163 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 500 ms 1.0 s 1.5 s 2.0 s FCP 1.5 s LCP 2.4 shttps://cdn.kastatic.org/khanacademy/fonts/d45d409d2fa42169-LatoLatin-Regular.woff2d45d409d2fa42169-LatoLa... https://cdn.kastatic.org/khanacademy/fonts/d45d409d2fa42169-LatoLatin-Regular.woff2 — 43.4 KiB — 0 ms — font-display: swaphttps://cdn.kastatic.org/khanacademy/fonts/1cf13853095a62e2-LatoLatin-Bold.woff21cf13853095a62e2-LatoLa... https://cdn.kastatic.org/khanacademy/fonts/1cf13853095a62e2-LatoLatin-Bold.woff2 — 43.8 KiB — 0 ms — font-display: swaphttps://cdn.kastatic.org/khanacademy/fonts/b430c69579ae2887-SourceSerifPro-Semibold.woff2b430c69579ae2887-Source... https://cdn.kastatic.org/khanacademy/fonts/b430c69579ae2887-SourceSerifPro-Semibold.woff2 — 16.0 KiB — 0 ms — font-display: swaphttps://cdn.kastatic.org/khanacademy/fonts/03ac24f73354c182-SourceSerifPro-Regular.woff203ac24f73354c182-Source... https://cdn.kastatic.org/khanacademy/fonts/03ac24f73354c182-SourceSerifPro-Regular.woff2 — 15.5 KiB — 0 ms — font-display: swaphttps://cdn.kastatic.org/khanacademy/fonts/71fc01820777da89-LatoLatin-Italic.woff271fc01820777da89-LatoLa... https://cdn.kastatic.org/khanacademy/fonts/71fc01820777da89-LatoLatin-Italic.woff2 — 44.7 KiB — 0 ms — font-display: swap
d45d409d2fa42169-LatoLa... woff2 swap
Size 43 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
1cf13853095a62e2-LatoLa... woff2 swap
Size 44 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
b430c69579ae2887-Source... woff2 swap
Size 16 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
03ac24f73354c182-Source... woff2 swap
Size 16 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
71fc01820777da89-LatoLa... woff2 swap
Size 45 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
Network Waterfall
122 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
85% of JavaScript execution is third-party
First-party Third-party 1067ms · 903KB · $14/mo
cdn.kastatic.org
Other
Costly
Execution 655ms
Transfer 716 KB
Unused 56%
Monthly Cost $9/mo
Unattributable
Other
Costly
Execution 206ms
Transfer 0 KB
Monthly Cost $3/mo
cdn.kastatic.org
Other
Optional
Execution 152ms
Transfer 37 KB
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 54ms
Transfer 151 KB
Unused 58%
Monthly Cost $1/mo

These scripts may cost more than they're worth

  • cdn.kastatic.org adds 655ms and costs ~$9/month
  • Unattributable adds 206ms and costs ~$3/month

85% 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

cdn.kastatic.org takes 655ms 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

56% of cdn.kastatic.org'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 206ms 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

58% 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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