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Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
85
GRADE
B
FIX
1
REVIEW
7
PASS
7
INFO
2

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

Mobile Desktop
63
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.
100
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.

1.96 s

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

7.82 s

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

426 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.

3.43 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.

7.85 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
17
7 PASS 7 REVIEW 1 FIX
D
Third-Party Impact
Action
100% third-party, 0 ms blocking
FIX
100% third-party, 0 ms blocking
Warning::
Third-party code accounts for 100% of page weight (1.1 MiB of 1.1 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
B
Page Weight Budget
1.1 MB transferred, 67 requests
REVIEW
1.1 MB transferred, 67 requests
Info::
Page weighs 2.5 MB (1.1 MB transferred)
Warning::
JavaScript is 542 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 542 KB
Info::
Fonts are 314 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 314 KB
Info::
67 HTTP requests
Info::
Estimated 0.23 g CO2 per page load
1.1 MB / 2.4 MB budget
1.1 MB transferred
67 requests
0.23 g CO2 per page load
JavaScript 542.5 KiB 49%
Fonts 314.2 KiB 28%
Images 172.4 KiB 16%
HTML 42.8 KiB 4%
CSS 20.1 KiB 2%
Other 16.2 KiB 1%
Other 2.0 KiB 0%
Other 751 B 0%
0 2.4 MB 4.9 MB
Under 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

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

B
Image Optimization
34 images, 0 KB saveable
REVIEW
34 images, 0 KB saveable
Info::
All images are well-optimized
34 images 172 KB
0 oversized -0 KB
31 legacy format
0 missing dimensions CLS risk
C
JS Execution Cost
Action
1878ms total JS execution
REVIEW
1878ms total JS execution
Warning::
https://react.dev/_next/static/chunks/framework-76...: 504ms CPU time
Warning::
https://react.dev/: 438ms CPU time
Warning::
Unattributable: 346ms CPU time
Warning::
https://www.googletagmanager.com/gtag/js?id=G-B1E8...: 262ms CPU time
Info::
https://react.dev/_next/static/chunks/4ad82c5e.aa0...: 143ms CPU time
Warning::
Third-party scripts: 1878ms (100% of total)

Main Thread Breakdown

Script Evaluation 51% Other 21% Style & Layout 18% Script Parsing & Compilation 7%
ScriptTotalScriptingParse/CompileParty
https://react.dev/_next/static/chunks/framework-76ad44d61c11f057.js504ms439ms15ms3rd
https://react.dev/438ms21ms7ms3rd
Unattributable346ms13ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=G-B1E83PJ3RT262ms221ms39ms3rd
https://react.dev/_next/static/chunks/4ad82c5e.aa059996e264f809.js143ms131ms12ms3rd
https://react.dev/_next/static/chunks/main-8bc660a98b463b2d.js97ms86ms11ms3rd
https://react.dev/_next/static/chunks/pages/%5B%5B...markdownPath%5D%5D-ef91ae665155f68d.js88ms86ms1ms3rd
C
JS Bundles
Action
13 scripts, 209 KB unused
REVIEW
13 scripts, 209 KB unused
Warning::
https://www.googletagmanager.com/gtag/js?id=G-B1E8...: 62 KB unused (43%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://react.dev/_next/static/chunks/4ad82c5e.aa0...: 45 KB unused (90%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://react.dev/_next/static/chunks/811.b2e5ca62...: 44 KB unused (40%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://react.dev/_next/static/chunks/928-e89de0bd...: 32 KB unused (34%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://react.dev/_next/static/chunks/668-9be9de6f...: 26 KB unused (76%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 209 KB
209 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtag/js?id=G-B1E83PJ3RT146 KB62 KB (43%)✓3rd
https://react.dev/_next/static/chunks/4ad82c5e.aa059996e264f809.js50 KB45 KB (90%)✓3rd
https://react.dev/_next/static/chunks/811.b2e5ca620a3f883e.js110 KB44 KB (40%)✓3rd
https://react.dev/_next/static/chunks/928-e89de0bd2e20fa8c.js94 KB32 KB (34%)✓3rd
https://react.dev/_next/static/chunks/668-9be9de6fa7660277.js34 KB26 KB (76%)✓3rd
https://react.dev/_next/static/chunks/main-8bc660a98b463b2d.js39 KB—✓3rd
https://react.dev/_next/static/chunks/pages/_app-6d7b64b3b21a9551.js1 KB—✓3rd
https://react.dev/_next/static/chunks/pages/%5B%5B...markdownPath%5D%5D-ef91ae665155f68d.js3 KB—✓3rd
https://react.dev/_next/static/MNWyTLE_bcVMjrXmgoiBA/_buildManifest.js1 KB—✓3rd
https://react.dev/_next/static/MNWyTLE_bcVMjrXmgoiBA/_ssgManifest.js0 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

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
Page Weight Inventory
67 resources · 1.1 MB · 209 KB savings available
REVIEW
67 resources · 1.1 MB · 209 KB savings available
Warning::
Page weight 87 KB over 1MB target
Got: 1.1 MB Expected: ≤ 1 MB
Info::
~209 KB of savings available
Warning::
66 third-party resources (100% of weight)
67 resources · 1.1 MiB · 66 third-party 87.0 KiB over 1MB target
JavaScript 49% · 542.5 KiB
Font 28% · 314.2 KiB
Image 16% · 174.3 KiB
Document 4% · 43.0 KiB
CSS 2% · 20.1 KiB
Other 2% · 16.9 KiB

~208.7 KiB of savings available

Remove unused JavaScript: 208.7 KiB
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

B
HTTP Caching
public, max-age=0, must-revalidate
REVIEW
public, max-age=0, must-revalidate
Info::
Cache-Control header is set
Got: public, max-age=0, must-revalidate
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

public, max-age=0, must-revalidate

DirectiveValueMeaning
public—Any cache may store this response
max-age0Cache for 0 seconds
must-revalidate—Must recheck with server after expiry
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
9 fonts (314 KB)
PASS
9 fonts (314 KB)
Info::
9 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

9

314 KB total

Render-blocking

0

of 9

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 4.0 s 5.0 s 6.0 s 7.0 s 8.0 s FCP 2.0 s LCP 7.8 shttps://react.dev/fonts/Source-Code-Pro-Regular.woff2Source-Code-Pro-Regular... https://react.dev/fonts/Source-Code-Pro-Regular.woff2 — 74.8 KiB — 60 ms — font-display: swaphttps://react.dev/fonts/Source-Code-Pro-Bold.woff2Source-Code-Pro-Bold.woff2 https://react.dev/fonts/Source-Code-Pro-Bold.woff2 — 75.8 KiB — 57 ms — font-display: swaphttps://react.dev/fonts/Optimistic_Display_W_Md.woff2Optimistic_Display_W_Md... https://react.dev/fonts/Optimistic_Display_W_Md.woff2 — 23.1 KiB — 26 ms — font-display: swaphttps://react.dev/fonts/Optimistic_Display_W_SBd.woff2Optimistic_Display_W_SB... https://react.dev/fonts/Optimistic_Display_W_SBd.woff2 — 23.3 KiB — 42 ms — font-display: swaphttps://react.dev/fonts/Optimistic_Display_W_Bd.woff2Optimistic_Display_W_Bd... https://react.dev/fonts/Optimistic_Display_W_Bd.woff2 — 23.3 KiB — 30 ms — font-display: swaphttps://react.dev/fonts/Optimistic_Text_W_Md.woff2Optimistic_Text_W_Md.woff2 https://react.dev/fonts/Optimistic_Text_W_Md.woff2 — 23.2 KiB — 119 ms — font-display: swaphttps://react.dev/fonts/Optimistic_Text_W_Bd.woff2Optimistic_Text_W_Bd.woff2 https://react.dev/fonts/Optimistic_Text_W_Bd.woff2 — 23.2 KiB — 51 ms — font-display: swaphttps://react.dev/fonts/Optimistic_Text_W_Rg.woff2Optimistic_Text_W_Rg.woff2 https://react.dev/fonts/Optimistic_Text_W_Rg.woff2 — 22.3 KiB — 31 ms — font-display: swaphttps://react.dev/fonts/Optimistic_Text_W_It.woff2Optimistic_Text_W_It.woff2 https://react.dev/fonts/Optimistic_Text_W_It.woff2 — 25.3 KiB — 53 ms — font-display: swap
Source-Code-Pro-Regular... woff2 swap
Size 75 KB
Load time 60 ms
Start 150 ms
Risk FOUT — text flashes from fallback to web font
Source-Code-Pro-Bold.woff2 woff2 swap
Size 76 KB
Load time 57 ms
Start 150 ms
Risk FOUT — text flashes from fallback to web font
Optimistic_Display_W_Md... woff2 swap
Size 23 KB
Load time 26 ms
Start 150 ms
Risk FOUT — text flashes from fallback to web font
Optimistic_Display_W_SB... woff2 swap
Size 23 KB
Load time 42 ms
Start 150 ms
Risk FOUT — text flashes from fallback to web font
Optimistic_Display_W_Bd... woff2 swap
Size 23 KB
Load time 30 ms
Start 151 ms
Risk FOUT — text flashes from fallback to web font
Optimistic_Text_W_Md.woff2 woff2 swap
Size 23 KB
Load time 119 ms
Start 151 ms
Risk FOUT — text flashes from fallback to web font
Optimistic_Text_W_Bd.woff2 woff2 swap
Size 23 KB
Load time 51 ms
Start 151 ms
Risk FOUT — text flashes from fallback to web font
Optimistic_Text_W_Rg.woff2 woff2 swap
Size 22 KB
Load time 31 ms
Start 151 ms
Risk FOUT — text flashes from fallback to web font
Optimistic_Text_W_It.woff2 woff2 swap
Size 25 KB
Load time 53 ms
Start 152 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
38 hints, 0 missing preconnects
PASS
38 hints, 0 missing preconnects
Info::
Page uses 38 resource hint(s)

Current Resource Hints

preconnect
1
preload
+27
37
dns-prefetch
—
prefetch
—

38 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
67 requests over 1386ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s 6.0 s 7.0 s 8.0 s FCP 2.0 s LCP 7.8 shttps://reactjs.org// https://reactjs.org/ — 308 — 215 B — 65 ms — h2https://react.dev/react.dev/ https://react.dev/ — 200 — 42.8 KiB — 72 ms — h2https://www.googletagmanager.com/gtag/js?id=G-B1E83PJ3RTwww.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-B1E83PJ3RT — 200 — 146.5 KiB — 163 ms — h2https://react.dev/fonts/Source-Code-Pro-Regular.woff2react.dev/fonts/Source-Code-Pro-Reg... https://react.dev/fonts/Source-Code-Pro-Regular.woff2 — 200 — 74.8 KiB — 60 ms — h2https://react.dev/fonts/Source-Code-Pro-Bold.woff2react.dev/fonts/Source-Code-Pro-Bol... https://react.dev/fonts/Source-Code-Pro-Bold.woff2 — 200 — 75.8 KiB — 57 ms — h2https://react.dev/fonts/Optimistic_Display_W_Md.woff2react.dev/fonts/Optimistic_Display_... https://react.dev/fonts/Optimistic_Display_W_Md.woff2 — 200 — 23.1 KiB — 26 ms — h2https://react.dev/fonts/Optimistic_Display_W_SBd.woff2react.dev/fonts/Optimistic_Display_... https://react.dev/fonts/Optimistic_Display_W_SBd.woff2 — 200 — 23.3 KiB — 42 ms — h2https://react.dev/fonts/Optimistic_Display_W_Bd.woff2react.dev/fonts/Optimistic_Display_... https://react.dev/fonts/Optimistic_Display_W_Bd.woff2 — 200 — 23.3 KiB — 30 ms — h2https://react.dev/fonts/Optimistic_Text_W_Md.woff2react.dev/fonts/Optimistic_Text_W_M... https://react.dev/fonts/Optimistic_Text_W_Md.woff2 — 200 — 23.2 KiB — 119 ms — h2https://react.dev/fonts/Optimistic_Text_W_Bd.woff2react.dev/fonts/Optimistic_Text_W_B... https://react.dev/fonts/Optimistic_Text_W_Bd.woff2 — 200 — 23.2 KiB — 51 ms — h2https://react.dev/fonts/Optimistic_Text_W_Rg.woff2react.dev/fonts/Optimistic_Text_W_R... https://react.dev/fonts/Optimistic_Text_W_Rg.woff2 — 200 — 22.3 KiB — 31 ms — h2https://react.dev/fonts/Optimistic_Text_W_It.woff2react.dev/fonts/Optimistic_Text_W_I... https://react.dev/fonts/Optimistic_Text_W_It.woff2 — 200 — 25.3 KiB — 53 ms — h2https://react.dev/_next/static/css/08c63e3f3aafb0fb.cssreact.dev/_next/static/css/08c63e3f... https://react.dev/_next/static/css/08c63e3f3aafb0fb.css — 200 — 20.1 KiB — 26 ms — h2https://react.dev/_next/image?url=%2Fimages%2Fuwu.png&w=640&q=75react.dev/_next/image?url=%2Fimages... https://react.dev/_next/image?url=%2Fimages%2Fuwu.png&w=640&q=75 — 200 — 21.5 KiB — 53 ms — h2https://react.dev/images/home/conf2021/cover.svgreact.dev/images/home/conf2021/cove... https://react.dev/images/home/conf2021/cover.svg — 200 — 727 B — 27 ms — h2https://react.dev/images/home/conf2021/andrew.jpgreact.dev/images/home/conf2021/andr... https://react.dev/images/home/conf2021/andrew.jpg — 200 — 2.2 KiB — 25 ms — h2https://react.dev/images/home/conf2021/lauren.jpgreact.dev/images/home/conf2021/laur... https://react.dev/images/home/conf2021/lauren.jpg — 200 — 5.7 KiB — 41 ms — h2https://react.dev/images/home/conf2021/juan.jpgreact.dev/images/home/conf2021/juan... https://react.dev/images/home/conf2021/juan.jpg — 200 — 1.2 KiB — 38 ms — h2https://react.dev/site.webmanifestreact.dev/site.webmanifest https://react.dev/site.webmanifest — 200 — 751 B — 119 ms — h2https://react.dev/_next/image?url=%2Fimages%2Fuwu.png&w=128&q=75react.dev/_next/image?url=%2Fimages... https://react.dev/_next/image?url=%2Fimages%2Fuwu.png&w=128&q=75 — 200 — 4.1 KiB — 85 ms — h2https://react.dev/_next/static/chunks/webpack-c9ab623dfe839ebe.jsreact.dev/_next/static/chunks/webpa... https://react.dev/_next/static/chunks/webpack-c9ab623dfe839ebe.js — 200 — 2.4 KiB — 39 ms — h2https://react.dev/_next/static/chunks/framework-76ad44d61c11f057.jsreact.dev/_next/static/chunks/frame... https://react.dev/_next/static/chunks/framework-76ad44d61c11f057.js — 200 — 57.3 KiB — 95 ms — h2https://react.dev/_next/static/chunks/main-8bc660a98b463b2d.jsreact.dev/_next/static/chunks/main-... https://react.dev/_next/static/chunks/main-8bc660a98b463b2d.js — 200 — 38.6 KiB — 56 ms — h2https://react.dev/_next/static/chunks/pages/_app-6d7b64b3b21a9551.jsreact.dev/_next/static/chunks/pages... https://react.dev/_next/static/chunks/pages/_app-6d7b64b3b21a9551.js — 200 — 1.0 KiB — 33 ms — h2https://react.dev/_next/static/chunks/668-9be9de6fa7660277.jsreact.dev/_next/static/chunks/668-9... https://react.dev/_next/static/chunks/668-9be9de6fa7660277.js — 200 — 34.0 KiB — 80 ms — h2https://react.dev/_next/static/chunks/928-e89de0bd2e20fa8c.jsreact.dev/_next/static/chunks/928-e... https://react.dev/_next/static/chunks/928-e89de0bd2e20fa8c.js — 200 — 93.9 KiB — 89 ms — h2https://react.dev/_next/static/chunks/pages/%5B%5B...markdownPath%5D%5D-ef91ae665155f68d.jsreact.dev/_next/static/chunks/pages... https://react.dev/_next/static/chunks/pages/%5B%5B...markdownPath%5D%5D-ef91ae665155f68d.js — 200 — 3.4 KiB — 85 ms — h2https://react.dev/_next/static/MNWyTLE_bcVMjrXmgoiBA/_buildManifest.jsreact.dev/_next/static/MNWyTLE_bcVM... https://react.dev/_next/static/MNWyTLE_bcVMjrXmgoiBA/_buildManifest.js — 200 — 850 B — 35 ms — h2https://react.dev/_next/static/MNWyTLE_bcVMjrXmgoiBA/_ssgManifest.jsreact.dev/_next/static/MNWyTLE_bcVM... https://react.dev/_next/static/MNWyTLE_bcVMjrXmgoiBA/_ssgManifest.js — 200 — 406 B — 40 ms — h2https://react.dev/images/uwu.pngreact.dev/images/uwu.png https://react.dev/images/uwu.png — 200 — 54.0 KiB — 34 ms — h2
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s 6.0 s 7.0 s 8.0 s FCP 2.0 s LCP 7.8 shttps://reactjs.org// https://reactjs.org/ — 308 — 215 B — 65 ms — h2https://react.dev/react.dev/ https://react.dev/ — 200 — 42.8 KiB — 72 ms — h2https://www.googletagmanager.com/gtag/js?id=G-B1E83PJ3RTwww.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-B1E83PJ3RT — 200 — 146.5 KiB — 163 ms — h2https://react.dev/fonts/Source-Code-Pro-Regular.woff2react.dev/fonts/Source-Code-Pro-Reg... https://react.dev/fonts/Source-Code-Pro-Regular.woff2 — 200 — 74.8 KiB — 60 ms — h2https://react.dev/fonts/Source-Code-Pro-Bold.woff2react.dev/fonts/Source-Code-Pro-Bol... https://react.dev/fonts/Source-Code-Pro-Bold.woff2 — 200 — 75.8 KiB — 57 ms — h2https://react.dev/fonts/Optimistic_Display_W_Md.woff2react.dev/fonts/Optimistic_Display_... https://react.dev/fonts/Optimistic_Display_W_Md.woff2 — 200 — 23.1 KiB — 26 ms — h2https://react.dev/fonts/Optimistic_Display_W_SBd.woff2react.dev/fonts/Optimistic_Display_... https://react.dev/fonts/Optimistic_Display_W_SBd.woff2 — 200 — 23.3 KiB — 42 ms — h2https://react.dev/fonts/Optimistic_Display_W_Bd.woff2react.dev/fonts/Optimistic_Display_... https://react.dev/fonts/Optimistic_Display_W_Bd.woff2 — 200 — 23.3 KiB — 30 ms — h2https://react.dev/fonts/Optimistic_Text_W_Md.woff2react.dev/fonts/Optimistic_Text_W_M... https://react.dev/fonts/Optimistic_Text_W_Md.woff2 — 200 — 23.2 KiB — 119 ms — h2https://react.dev/fonts/Optimistic_Text_W_Bd.woff2react.dev/fonts/Optimistic_Text_W_B... https://react.dev/fonts/Optimistic_Text_W_Bd.woff2 — 200 — 23.2 KiB — 51 ms — h2https://react.dev/fonts/Optimistic_Text_W_Rg.woff2react.dev/fonts/Optimistic_Text_W_R... https://react.dev/fonts/Optimistic_Text_W_Rg.woff2 — 200 — 22.3 KiB — 31 ms — h2https://react.dev/fonts/Optimistic_Text_W_It.woff2react.dev/fonts/Optimistic_Text_W_I... https://react.dev/fonts/Optimistic_Text_W_It.woff2 — 200 — 25.3 KiB — 53 ms — h2https://react.dev/_next/static/css/08c63e3f3aafb0fb.cssreact.dev/_next/static/css/08c63e3f... https://react.dev/_next/static/css/08c63e3f3aafb0fb.css — 200 — 20.1 KiB — 26 ms — h2https://react.dev/_next/image?url=%2Fimages%2Fuwu.png&w=640&q=75react.dev/_next/image?url=%2Fimages... https://react.dev/_next/image?url=%2Fimages%2Fuwu.png&w=640&q=75 — 200 — 21.5 KiB — 53 ms — h2https://react.dev/images/home/conf2021/cover.svgreact.dev/images/home/conf2021/cove... https://react.dev/images/home/conf2021/cover.svg — 200 — 727 B — 27 ms — h2https://react.dev/images/home/conf2021/andrew.jpgreact.dev/images/home/conf2021/andr... https://react.dev/images/home/conf2021/andrew.jpg — 200 — 2.2 KiB — 25 ms — h2https://react.dev/images/home/conf2021/lauren.jpgreact.dev/images/home/conf2021/laur... https://react.dev/images/home/conf2021/lauren.jpg — 200 — 5.7 KiB — 41 ms — 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HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
100% of JavaScript execution is third-party
First-party Third-party 1878ms · 339KB · €20/mo
react.dev
Other
Costly
Execution 504ms
Transfer 57 KB
Monthly Cost €5/mo
react.dev
Other
Costly
Execution 438ms
Transfer 43 KB
Monthly Cost €5/mo
Unattributable
Other
Costly
Execution 346ms
Transfer 0 KB
Monthly Cost €4/mo
Google Tag Manager
Tag Manager
Costly
Execution 262ms
Transfer 146 KB
Unused 43%
Monthly Cost €3/mo
react.dev
Other
Optional
Execution 143ms
Transfer 50 KB
Unused 90%
Monthly Cost €2/mo
react.dev
Other
Optional
Execution 97ms
Transfer 39 KB
Monthly Cost €1/mo
react.dev
Other
Optional
Execution 88ms
Transfer 3 KB
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • react.dev adds 504ms and costs ~€5/month
  • react.dev adds 438ms and costs ~€5/month
  • Unattributable adds 346ms and costs ~€4/month
  • Google Tag Manager adds 262ms and costs ~€3/month

100% 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

react.dev takes 504ms 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

react.dev takes 438ms 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

Unattributable takes 346ms 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 262ms 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

90% of react.dev'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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