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https://sizzlejs.com

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
83
GRADE
B
FIX
2
REVIEW
4
PASS
7
INFO
2

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

Mobile Desktop
89
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.
100
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.

1.20 s

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

1.76 s

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

0 ms

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

0.002

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

1.30 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.

1.76 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
15
7 PASS 4 REVIEW 2 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 (1.2 MiB of 1.2 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
HTTP Caching
Action
No cache headers
FIX
No cache headers
Warning::
No Cache-Control header found
Browsers will use heuristic caching, which can be unpredictable. Set explicit cache headers.

No Cache-Control header

Adding a Cache-Control header can significantly improve repeat-visit performance.

B
Page Weight Budget
1.2 MB transferred, 117 requests
REVIEW
1.2 MB transferred, 117 requests
Info::
Page weighs 5.3 MB (1.2 MB transferred)
Warning::
JavaScript is 994 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 994 KB
Warning::
117 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.26 g CO2 per page load
1.2 MB / 2.4 MB budget
1.2 MB transferred
117 requests
0.26 g CO2 per page load
JavaScript 993.6 KiB 79%
CSS 187.0 KiB 15%
HTML 51.8 KiB 4%
Other 17.3 KiB 1%
Other 4.4 KiB 0%
Other 935 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

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

B
JS Execution Cost
604ms total JS execution
REVIEW
604ms total JS execution
Warning::
https://github.com/jquery/sizzle/wiki: 444ms CPU time
Info::
Unattributable: 85ms CPU time
Info::
https://github.githubassets.com/assets/behaviors-e...: 75ms CPU time
Warning::
Third-party scripts: 604ms (100% of total)

Main Thread Breakdown

Style & Layout 46% Script Evaluation 27% Other 12% Script Parsing & Compilation 7% Rendering 4% Parse HTML & CSS 3%
ScriptTotalScriptingParse/CompileParty
https://github.com/jquery/sizzle/wiki444ms1ms0ms3rd
Unattributable85ms1ms0ms3rd
https://github.githubassets.com/assets/behaviors-e2f9128395d9f8b3.js75ms37ms4ms3rd
C
JS Bundles
Action
88 scripts, 238 KB unused
REVIEW
88 scripts, 238 KB unused
Warning::
https://github.githubassets.com/assets/primer-reac...: 66 KB unused (53%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://github.githubassets.com/assets/react-lib-e...: 63 KB unused (73%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://github.githubassets.com/assets/react-core-...: 44 KB unused (75%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://github.githubassets.com/assets/behaviors-e...: 43 KB unused (80%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://github.githubassets.com/assets/53102-7adf5...: 21 KB unused (70%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 238 KB
238 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://github.githubassets.com/assets/primer-react-6dbbf6a6b62127f5.js124 KB66 KB (53%)✓3rd
https://github.githubassets.com/assets/react-lib-e36eebdcabb31afd.js88 KB63 KB (73%)✓3rd
https://github.githubassets.com/assets/react-core-fa9bebcd564984e3.js59 KB44 KB (75%)✓3rd
https://github.githubassets.com/assets/behaviors-e2f9128395d9f8b3.js54 KB43 KB (80%)✓3rd
https://github.githubassets.com/assets/53102-7adf5a6968114b74.js31 KB21 KB (70%)✓3rd
https://github.githubassets.com/assets/19930-d7474e22a5e73a83.js4 KB—✓3rd
https://github.githubassets.com/assets/octicons-react-bb57c7bed5998408.js100 KB—✓3rd
https://github.githubassets.com/assets/fetch-utilities-23fca2e84f65970f.js3 KB—✓3rd
https://github.githubassets.com/assets/85924-e131bec5f99667e1.js5 KB—✓3rd
https://github.githubassets.com/assets/28839-734cb6d8a7150172.js6 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

C
Page Weight Inventory
Action
117 resources · 1.2 MB · 238 KB savings available
REVIEW
117 resources · 1.2 MB · 238 KB savings available
Warning::
Page weight 231 KB over 1MB target
Got: 1.2 MB Expected: ≤ 1 MB
Info::
~238 KB of savings available
Warning::
116 third-party resources (100% of weight)
117 resources · 1.2 MiB · 116 third-party 231.0 KiB over 1MB target
JavaScript 79% · 993.6 KiB
CSS 15% · 187.0 KiB
Document 4% · 51.8 KiB
Image 1% · 17.2 KiB
Other 0% · 5.5 KiB

~237.6 KiB of savings available

Remove unused JavaScript: 237.6 KiB
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
No images on this page
PASS
No images on this page
Info::
No images on this page
0 images 0 KB
0 oversized -0 KB
0 legacy format
0 missing dimensions CLS risk
A+
Font Loading
No web fonts (system fonts)
PASS
No web fonts (system fonts)
Info::
No web fonts loaded — system fonts are fastest
No web fonts loaded — system fonts are optimal.
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: Cloudflare

Network Waterfall
117 requests over 1721ms
INFO
0 ms 500 ms 1.0 s 1.5 s FCP 1.2 s LCP 1.8 shttps://sizzlejs.com// https://sizzlejs.com/ — 301 — 105 B — 57 ms — h2https://github.com/jquery/sizzle/wikigithub.com/jquery/sizzle/wiki https://github.com/jquery/sizzle/wiki — 200 — 51.8 KiB — 472 ms — h2https://github.githubassets.com/assets/light-8db8ec9d843a6198.cssgithub.githubassets.com/assets/ligh... https://github.githubassets.com/assets/light-8db8ec9d843a6198.css — 200 — 6.5 KiB — 44 ms — h2https://github.githubassets.com/assets/light_high_contrast-1ebc8c2fbf646f62.cssgithub.githubassets.com/assets/ligh... https://github.githubassets.com/assets/light_high_contrast-1ebc8c2fbf646f62.css — 200 — 6.6 KiB — 38 ms — h2https://github.githubassets.com/assets/dark-5a2079a7af880b5d.cssgithub.githubassets.com/assets/dark... https://github.githubassets.com/assets/dark-5a2079a7af880b5d.css — 200 — 6.6 KiB — 27 ms — h2https://github.githubassets.com/assets/dark_high_contrast-f22f15c407d6eca1.cssgithub.githubassets.com/assets/dark... https://github.githubassets.com/assets/dark_high_contrast-f22f15c407d6eca1.css — 200 — 6.9 KiB — 27 ms — h2https://github.githubassets.com/assets/primer-primitives-0f570a01cbe448fb.cssgithub.githubassets.com/assets/prim... https://github.githubassets.com/assets/primer-primitives-0f570a01cbe448fb.css — 200 — 2.3 KiB — 35 ms — h2https://github.githubassets.com/assets/primer-f638bd26ec06210f.cssgithub.githubassets.com/assets/prim... https://github.githubassets.com/assets/primer-f638bd26ec06210f.css — 200 — 42.3 KiB — 46 ms — h2https://github.githubassets.com/assets/global-38e9e8b8d7081236.cssgithub.githubassets.com/assets/glob... https://github.githubassets.com/assets/global-38e9e8b8d7081236.css — 200 — 40.3 KiB — 47 ms — h2https://github.githubassets.com/assets/github-cf5d2e35f4a0c3f5.cssgithub.githubassets.com/assets/gith... https://github.githubassets.com/assets/github-cf5d2e35f4a0c3f5.css — 200 — 23.7 KiB — 40 ms — h2https://github.githubassets.com/assets/repository-6ec84ae2261fecf8.cssgithub.githubassets.com/assets/repo... https://github.githubassets.com/assets/repository-6ec84ae2261fecf8.css — 200 — 5.4 KiB — 16 ms — h2https://github.githubassets.com/assets/wiki-3b8576bd4992bc25.cssgithub.githubassets.com/assets/wiki... https://github.githubassets.com/assets/wiki-3b8576bd4992bc25.css — 200 — 663 B — 22 ms — h2https://github.githubassets.com/assets/high-contrast-cookie-26d6bae49dfd2c29.jsgithub.githubassets.com/assets/high... https://github.githubassets.com/assets/high-contrast-cookie-26d6bae49dfd2c29.js — 200 — 847 B — 33 ms — h2https://github.githubassets.com/assets/react-core.8e8807bbcae141e7.module.cssgithub.githubassets.com/assets/reac... https://github.githubassets.com/assets/react-core.8e8807bbcae141e7.module.css — 200 — 436 B — 15 ms — h2https://github.githubassets.com/assets/primer-react-css.add9d698abe5ac23.module.cssgithub.githubassets.com/assets/prim... https://github.githubassets.com/assets/primer-react-css.add9d698abe5ac23.module.css — 200 — 34.3 KiB — 19 ms — h2https://github.githubassets.com/assets/notifications-subscriptions-menu.eafe1f00f7ea4df8.module.cssgithub.githubassets.com/assets/noti... https://github.githubassets.com/assets/notifications-subscriptions-menu.eafe1f00f7ea4df8.module.css — 200 — 1.1 KiB — 15 ms — h2https://github.githubassets.com/assets/keyboard-shortcuts-dialog.f28b62055c3637ed.module.cssgithub.githubassets.com/assets/keyb... https://github.githubassets.com/assets/keyboard-shortcuts-dialog.f28b62055c3637ed.module.css — 200 — 400 B — 14 ms — h2https://github.githubassets.com/assets/marketing-navigation.9b8d6525ad84b340.module.cssgithub.githubassets.com/assets/mark... https://github.githubassets.com/assets/marketing-navigation.9b8d6525ad84b340.module.css — 200 — 2.3 KiB — 12 ms — h2https://github.githubassets.com/assets/wp-runtime-afd6af4b76ea6963.jsgithub.githubassets.com/assets/wp-r... https://github.githubassets.com/assets/wp-runtime-afd6af4b76ea6963.js — 200 — 21.1 KiB — 3 ms — h3https://github.githubassets.com/assets/fetch-utilities-23fca2e84f65970f.jsgithub.githubassets.com/assets/fetc... https://github.githubassets.com/assets/fetch-utilities-23fca2e84f65970f.js — 200 — 3.4 KiB — 2 ms — h3https://github.githubassets.com/assets/85924-e131bec5f99667e1.jsgithub.githubassets.com/assets/8592... https://github.githubassets.com/assets/85924-e131bec5f99667e1.js — 200 — 5.4 KiB — 2 ms — h3https://github.githubassets.com/assets/28839-734cb6d8a7150172.jsgithub.githubassets.com/assets/2883... https://github.githubassets.com/assets/28839-734cb6d8a7150172.js — 200 — 6.1 KiB — 3 ms — h3https://github.githubassets.com/assets/34646-9e3e16bb1d35de16.jsgithub.githubassets.com/assets/3464... https://github.githubassets.com/assets/34646-9e3e16bb1d35de16.js — 200 — 6.7 KiB — 26 ms — h3https://github.githubassets.com/assets/environment-51c0968cf21c176d.jsgithub.githubassets.com/assets/envi... https://github.githubassets.com/assets/environment-51c0968cf21c176d.js — 200 — 7.5 KiB — 32 ms — h3https://github.githubassets.com/assets/runtime-helpers-3bb6f7d6b7a2f531.jsgithub.githubassets.com/assets/runt... https://github.githubassets.com/assets/runtime-helpers-3bb6f7d6b7a2f531.js — 200 — 1.5 KiB — 32 ms — h3https://github.githubassets.com/assets/2966-f6796bfd155feae1.jsgithub.githubassets.com/assets/2966... https://github.githubassets.com/assets/2966-f6796bfd155feae1.js — 200 — 7.3 KiB — 37 ms — h3https://github.githubassets.com/assets/96232-69d46a31854353d4.jsgithub.githubassets.com/assets/9623... https://github.githubassets.com/assets/96232-69d46a31854353d4.js — 200 — 3.7 KiB — 37 ms — h3https://github.githubassets.com/assets/41013-7a6deee6d6ff15eb.jsgithub.githubassets.com/assets/4101... https://github.githubassets.com/assets/41013-7a6deee6d6ff15eb.js — 200 — 5.4 KiB — 37 ms — h3https://github.githubassets.com/assets/51210-3abb7238871a5b29.jsgithub.githubassets.com/assets/5121... https://github.githubassets.com/assets/51210-3abb7238871a5b29.js — 200 — 4.6 KiB — 38 ms — h3https://github.githubassets.com/assets/64247-5fcfe92512e38512.jsgithub.githubassets.com/assets/6424... https://github.githubassets.com/assets/64247-5fcfe92512e38512.js — 200 — 7.6 KiB — 38 ms — h3
0 ms 500 ms 1.0 s 1.5 s FCP 1.2 s LCP 1.8 shttps://sizzlejs.com// https://sizzlejs.com/ — 301 — 105 B — 57 ms — h2https://github.com/jquery/sizzle/wikigithub.com/jquery/sizzle/wiki https://github.com/jquery/sizzle/wiki — 200 — 51.8 KiB — 472 ms — h2https://github.githubassets.com/assets/light-8db8ec9d843a6198.cssgithub.githubassets.com/assets/ligh... https://github.githubassets.com/assets/light-8db8ec9d843a6198.css — 200 — 6.5 KiB — 44 ms — h2https://github.githubassets.com/assets/light_high_contrast-1ebc8c2fbf646f62.cssgithub.githubassets.com/assets/ligh... https://github.githubassets.com/assets/light_high_contrast-1ebc8c2fbf646f62.css — 200 — 6.6 KiB — 38 ms — h2https://github.githubassets.com/assets/dark-5a2079a7af880b5d.cssgithub.githubassets.com/assets/dark... https://github.githubassets.com/assets/dark-5a2079a7af880b5d.css — 200 — 6.6 KiB — 27 ms — h2https://github.githubassets.com/assets/dark_high_contrast-f22f15c407d6eca1.cssgithub.githubassets.com/assets/dark... https://github.githubassets.com/assets/dark_high_contrast-f22f15c407d6eca1.css — 200 — 6.9 KiB — 27 ms — h2https://github.githubassets.com/assets/primer-primitives-0f570a01cbe448fb.cssgithub.githubassets.com/assets/prim... https://github.githubassets.com/assets/primer-primitives-0f570a01cbe448fb.css — 200 — 2.3 KiB — 35 ms — h2https://github.githubassets.com/assets/primer-f638bd26ec06210f.cssgithub.githubassets.com/assets/prim... https://github.githubassets.com/assets/primer-f638bd26ec06210f.css — 200 — 42.3 KiB — 46 ms — h2https://github.githubassets.com/assets/global-38e9e8b8d7081236.cssgithub.githubassets.com/assets/glob... https://github.githubassets.com/assets/global-38e9e8b8d7081236.css — 200 — 40.3 KiB — 47 ms — h2https://github.githubassets.com/assets/github-cf5d2e35f4a0c3f5.cssgithub.githubassets.com/assets/gith... https://github.githubassets.com/assets/github-cf5d2e35f4a0c3f5.css — 200 — 23.7 KiB — 40 ms — h2https://github.githubassets.com/assets/repository-6ec84ae2261fecf8.cssgithub.githubassets.com/assets/repo... https://github.githubassets.com/assets/repository-6ec84ae2261fecf8.css — 200 — 5.4 KiB — 16 ms — h2https://github.githubassets.com/assets/wiki-3b8576bd4992bc25.cssgithub.githubassets.com/assets/wiki... https://github.githubassets.com/assets/wiki-3b8576bd4992bc25.css — 200 — 663 B — 22 ms — h2https://github.githubassets.com/assets/high-contrast-cookie-26d6bae49dfd2c29.jsgithub.githubassets.com/assets/high... https://github.githubassets.com/assets/high-contrast-cookie-26d6bae49dfd2c29.js — 200 — 847 B — 33 ms — h2https://github.githubassets.com/assets/react-core.8e8807bbcae141e7.module.cssgithub.githubassets.com/assets/reac... https://github.githubassets.com/assets/react-core.8e8807bbcae141e7.module.css — 200 — 436 B — 15 ms — h2https://github.githubassets.com/assets/primer-react-css.add9d698abe5ac23.module.cssgithub.githubassets.com/assets/prim... 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https://github.githubassets.com/assets/wp-runtime-afd6af4b76ea6963.js — 200 — 21.1 KiB — 3 ms — h3https://github.githubassets.com/assets/fetch-utilities-23fca2e84f65970f.jsgithub.githubassets.com/assets/fetc... https://github.githubassets.com/assets/fetch-utilities-23fca2e84f65970f.js — 200 — 3.4 KiB — 2 ms — h3https://github.githubassets.com/assets/85924-e131bec5f99667e1.jsgithub.githubassets.com/assets/8592... https://github.githubassets.com/assets/85924-e131bec5f99667e1.js — 200 — 5.4 KiB — 2 ms — h3https://github.githubassets.com/assets/28839-734cb6d8a7150172.jsgithub.githubassets.com/assets/2883... https://github.githubassets.com/assets/28839-734cb6d8a7150172.js — 200 — 6.1 KiB — 3 ms — h3https://github.githubassets.com/assets/34646-9e3e16bb1d35de16.jsgithub.githubassets.com/assets/3464... https://github.githubassets.com/assets/34646-9e3e16bb1d35de16.js — 200 — 6.7 KiB — 26 ms — 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— 6 ms — h3https://api.github.com/_private/browser/statsapi.github.com/_private/browser/sta... https://api.github.com/_private/browser/stats — 200 — 0 B — 219 ms — h2https://collector.github.com/github/collectcollector.github.com/github/collect https://collector.github.com/github/collect — 204 — 467 B — 216 ms — h2
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 604ms · 106KB · €7/mo
github.com
Other
Costly
Execution 444ms
Transfer 52 KB
Monthly Cost €5/mo
Unattributable
Other
Optional
Execution 85ms
Transfer 0 KB
Monthly Cost €1/mo
github.githubassets.com
Other
Optional
Execution 75ms
Transfer 54 KB
Unused 80%
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • github.com adds 444ms and costs ~€5/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

github.com takes 444ms 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

80% of github.githubassets.com'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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