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Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
74
GRADE
C
FIX
5
REVIEW
2
PASS
7
INFO
2

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

Mobile Desktop
43
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.

6.43 s

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

10.12 s

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

658 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.

6.43 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.

10.47 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
7 PASS 2 REVIEW 5 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 163.8 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
D
JS Execution Cost
Action
2730ms total JS execution
FIX
2730ms total JS execution
Warning::
https://cdn.kastatic.org/khanacademy/khanacademy.d...: 1638ms CPU time
Warning::
Unattributable: 436ms CPU time
Warning::
https://www.khanacademy.org/: 319ms CPU time
Info::
https://cdn.kastatic.org/khanacademy/82289.7eff447...: 201ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-WSX...: 136ms CPU time
Warning::
Third-party scripts: 2411ms (88% of total)

Main Thread Breakdown

Script Evaluation 57% Other 18% Script Parsing & Compilation 11% Style & Layout 11%
ScriptTotalScriptingParse/CompileParty
https://cdn.kastatic.org/khanacademy/khanacademy.d010d00049edb0e5.js1638ms1253ms193ms3rd
Unattributable436ms40ms0ms3rd
https://www.khanacademy.org/319ms33ms29ms1st
https://cdn.kastatic.org/khanacademy/82289.7eff447bec28ae13.js201ms167ms2ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-WSX5PBP136ms92ms43ms3rd
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.js4 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/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://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://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/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/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
9 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

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 (164 KB)
PASS
5 fonts (164 KB)
Info::
5 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

5

164 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 FCP 6.4 s LCP 10.1 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 — 44.1 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 — 15.6 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
1 hints, 0 missing preconnects
PASS
1 hints, 0 missing preconnects
Info::
Page uses 1 resource hint(s)

Current Resource Hints

preconnect
—
preload
1
dns-prefetch
—
prefetch
—

1 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
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
88% of JavaScript execution is third-party
First-party Third-party 2411ms · 878KB · $32/mo
cdn.kastatic.org
Other
Costly
Execution 1638ms
Transfer 716 KB
Unused 56%
Monthly Cost $22/mo
Unattributable
Other
Costly
Execution 436ms
Transfer 0 KB
Monthly Cost $6/mo
cdn.kastatic.org
Other
Costly
Execution 201ms
Transfer 12 KB
Monthly Cost $3/mo
Google Tag Manager
Tag Manager
Optional
Execution 136ms
Transfer 151 KB
Unused 58%
Monthly Cost $2/mo

These scripts may cost more than they're worth

  • cdn.kastatic.org adds 1638ms and costs ~$22/month
  • Unattributable adds 436ms and costs ~$6/month
  • cdn.kastatic.org adds 201ms and costs ~$3/month

88% 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 1638ms 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 436ms 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

cdn.kastatic.org takes 201ms 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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