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https://codesandbox.io

Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
78
GRADE
C
FIX
3
REVIEW
2
PASS
9
INFO
2

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

Mobile Desktop
54
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
95
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
77
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.

1.21 s

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

20.85 s

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

731 ms

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

0.074

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

3.83 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.

21.77 s

Page Load Progression

461 ms
921 ms
1.4 s
1.8 s
2.3 s
2.8 s
3.2 s
3.7 s
Checks
16
9 PASS 2 REVIEW 3 FIX
F
Page Weight Budget
Action
3.8 MB transferred, 58 requests
FIX
3.8 MB transferred, 58 requests
Warning::
Page weighs 5.5 MB (3.8 MB transferred)
Info::
Fonts are 3.0 MB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 3.0 MB
Warning::
JavaScript is 637 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 637 KB
Info::
58 HTTP requests
Info::
Estimated 0.79 g CO2 per page load
3.8 MB / 2.4 MB budget
3.8 MB transferred
58 requests
0.79 g CO2 per page load
Fonts 3.0 MiB 80%
JavaScript 637.0 KiB 17%
Images 55.2 KiB 1%
HTML 37.9 KiB 1%
Other 15.8 KiB 0%
CSS 12.4 KiB 0%
Other 1.2 KiB 0%
Other 975 B 0%
0 2.4 MB 4.9 MB
Over budget

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

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 Execution Cost
Action
5658ms total JS execution
FIX
5658ms total JS execution
Warning::
https://codesandbox.io/: 2715ms CPU time
Warning::
https://codesandbox.io/_next/static/chunks/7157-f1...: 837ms CPU time
Warning::
https://codesandbox.io/cdn-cgi/challenge-platform/...: 501ms CPU time
Warning::
https://codesandbox.io/_next/static/chunks/3a1fbd1...: 469ms CPU time
Warning::
Unattributable: 414ms CPU time
Info::
Third-party scripts: 621ms (11% of total)

Main Thread Breakdown

Script Evaluation 34% Other 28% Style & Layout 22% Rendering 9% Script Parsing & Compilation 5%
ScriptTotalScriptingParse/CompileParty
https://codesandbox.io/2715ms70ms5ms1st
https://codesandbox.io/_next/static/chunks/7157-f1dd02184197292d.js837ms766ms18ms1st
https://codesandbox.io/cdn-cgi/challenge-platform/scripts/jsd/main.js501ms481ms3ms1st
https://codesandbox.io/_next/static/chunks/3a1fbd1c-9a309fde5120dbc5.js469ms153ms21ms1st
Unattributable414ms14ms0ms3rd
https://codesandbox.io/_next/static/chunks/app/page-e4cb27a7a3b23bcf.js207ms197ms5ms1st
https://static.cloudflareinsights.com/beacon.min.js/v8c78df7c7c0f484497ecbca7046644da1771523124516207ms36ms8ms3rd
https://codesandbox.io/_next/static/chunks/9331-ab608ee9ae01eddb.js157ms124ms32ms1st
https://codesandbox.io/_next/static/chunks/1261-d0847cd35a4e9b63.js100ms86ms4ms1st
https://codesandbox.io/_next/static/chunks/ef9c525d-794586603a2cf360.js52ms30ms21ms1st
D
JS Bundles
Action
26 scripts, 317 KB unused
FIX
26 scripts, 317 KB unused
Warning::
https://codesandbox.io/_next/static/chunks/9230-85...: 85 KB unused (96%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://codesandbox.io/_next/static/chunks/9331-ab...: 69 KB unused (55%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://codesandbox.io/_next/static/chunks/ec0da94...: 45 KB unused (90%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://codesandbox.io/_next/static/chunks/2409-a2...: 36 KB unused (73%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://codesandbox.io/_next/static/chunks/ef9c525...: 34 KB unused (77%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 317 KB
317 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://codesandbox.io/_next/static/chunks/9230-85da48510973f4ae.js89 KB85 KB (96%)✓1st
https://codesandbox.io/_next/static/chunks/9331-ab608ee9ae01eddb.js126 KB69 KB (55%)✓1st
https://codesandbox.io/_next/static/chunks/ec0da940-7fe13e19c1ef37bc.js51 KB45 KB (90%)✓1st
https://codesandbox.io/_next/static/chunks/2409-a2745fd5e5a7ed70.js50 KB36 KB (73%)✓1st
https://codesandbox.io/_next/static/chunks/ef9c525d-794586603a2cf360.js45 KB34 KB (77%)✓1st
https://codesandbox.io/_next/static/chunks/3037-34ebfe82f03e16ac.js33 KB24 KB (75%)✓1st
https://codesandbox.io/_next/static/chunks/e332d428-607a0fc2b0f712b1.js34 KB22 KB (67%)✓1st
https://codesandbox.io/_next/static/chunks/9348-4ca373a6936773be.js3 KB—✓1st
https://codesandbox.io/_next/static/chunks/1261-d0847cd35a4e9b63.js10 KB—✓1st
https://codesandbox.io/_next/static/chunks/f923c8e2-e4529f531e4e04c4.js1 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
Image Optimization
18 images, 0 KB saveable
REVIEW
18 images, 0 KB saveable
Info::
All images are well-optimized
18 images 55 KB
0 oversized -0 KB
8 legacy format
0 missing dimensions CLS risk
B
HTTP Caching
s-maxage=31536000, stale-while-revalidate
REVIEW
s-maxage=31536000, stale-while-revalidate
Info::
Cache-Control header is set
Got: s-maxage=31536000, stale-while-revalidate
Info::
CDN TTL: 52 weeks (s-maxage=31536000)
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

s-maxage=31536000, stale-while-revalidate

DirectiveValueMeaning
s-maxage31536000CDN caches for 52 weeks
stale-while-revalidate—Serve stale while revalidating
A+
Third-Party Impact
2% third-party, 0 ms blocking
PASS
2% third-party, 0 ms blocking
Info::
Third-party code accounts for 2% of page weight (58.8 KiB of 3.8 MiB)
Info::
Third-party blocking time is low (0 ms)
98%
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
3 fonts (3089 KB)
PASS
3 fonts (3089 KB)
Info::
3 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

3

3089 KB total

Render-blocking

0

of 3

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 1.2 s LCP 20.9 shttps://codesandbox.io/_next/static/media/e4af272ccee01ff0-s.p.woff2e4af272ccee01ff0-s.p.woff2 https://codesandbox.io/_next/static/media/e4af272ccee01ff0-s.p.woff2 — 47.4 KiB — 0 ms — font-display: swaphttps://codesandbox.io/_next/static/media/material-symbols-outlined.43ee5b2a.woff2material-symbols-outlin... https://codesandbox.io/_next/static/media/material-symbols-outlined.43ee5b2a.woff2 — 2.9 MiB — 0 ms — font-display: swaphttps://codesandbox.io/new/fonts/TWKEverett-Medium-web.woff2TWKEverett-Medium-web.w... https://codesandbox.io/new/fonts/TWKEverett-Medium-web.woff2 — 59.9 KiB — 0 ms — font-display: swap
e4af272ccee01ff0-s.p.woff2 woff2 swap
Size 47 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
material-symbols-outlin... woff2 swap
Size 2982 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
TWKEverett-Medium-web.w... woff2 swap
Size 60 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)

Fixing the unchecked items could save ~1491 KB and ~2982 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
2 hints, 0 missing preconnects
PASS
2 hints, 0 missing preconnects
Info::
Page uses 2 resource hint(s)

Current Resource Hints

preconnect
—
preload
2
dns-prefetch
—
prefetch
—

2 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
A+
Green Hosting
Whether the site is served from green-energy infrastructure
PASS

Green Hosting

This site is hosted on green energy infrastructure

Provider: Cloudflare

Network Waterfall
58 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
11% of JavaScript execution is third-party
First-party Third-party 621ms · 11KB · kr1145/mo
Unattributable
Other
Costly
Execution 414ms
Transfer 0 KB
Monthly Cost kr764/mo
static.cloudflareinsights.com
Other
Costly
Execution 207ms
Transfer 11 KB
Monthly Cost kr381/mo

These scripts may cost more than they're worth

  • Unattributable adds 414ms and costs ~kr764/month
  • static.cloudflareinsights.com adds 207ms and costs ~kr381/month

Unattributable takes 414ms 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

static.cloudflareinsights.com takes 207ms 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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