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https://www.swift.org

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
91
GRADE
A
FIX
0
REVIEW
3
PASS
9
INFO
2

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

Mobile Desktop
96
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.
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.

581 ms

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

1.37 s

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

53 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.

581 ms

Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.

1.60 s

Page Load Progression

381 ms
761 ms
1.1 s
1.5 s
1.9 s
2.3 s
2.7 s
3.0 s
Checks
14
9 PASS 3 REVIEW
B
Image Optimization
16 images, 0 KB saveable
REVIEW
16 images, 0 KB saveable
Info::
All images are well-optimized
16 images 376 KB
0 oversized -0 KB
10 legacy format
0 missing dimensions CLS risk
C
JS Execution Cost
Action
1378ms total JS execution
REVIEW
1378ms total JS execution
Warning::
https://www.swift.org/assets/javascripts/new-javas...: 1215ms CPU time
Info::
https://www.swift.org/assets/javascripts/new-javas...: 59ms CPU time
Info::
https://www.swift.org/: 54ms CPU time
Info::
Unattributable: 50ms CPU time
Info::
Third-party scripts: 50ms (4% of total)

Main Thread Breakdown

Other 86% Script Evaluation 6% Style & Layout 4%
ScriptTotalScriptingParse/CompileParty
https://www.swift.org/assets/javascripts/new-javascripts/vendor/anime.iife.min.js1215ms39ms2ms1st
https://www.swift.org/assets/javascripts/new-javascripts/hero.js59ms20ms0ms1st
https://www.swift.org/54ms14ms0ms1st
Unattributable50ms1ms0ms3rd
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A
Page Weight Budget
1013 KB transferred, 32 requests
PASS
1013 KB transferred, 32 requests
Info::
Page weighs 1.1 MB (1013 KB transferred)
Info::
32 HTTP requests
Info::
Estimated 0.21 g CO2 per page load
1013 KB / 2.4 MB budget
1013 KB transferred
32 requests
0.21 g CO2 per page load
Other 431.4 KiB 43%
Images 376.4 KiB 37%
JavaScript 179.4 KiB 18%
CSS 16.5 KiB 2%
HTML 9.3 KiB 1%
0 2.4 MB 4.9 MB
Under budget
A+
Third-Party Impact
8% third-party, 0 ms blocking
PASS
8% third-party, 0 ms blocking
Info::
Third-party code accounts for 8% of page weight (84.7 KiB of 1012.9 KiB)
Info::
Third-party blocking time is low (0 ms)
92%
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
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
JS Bundles
6 scripts, 44 KB unused
PASS
6 scripts, 44 KB unused
Warning::
https://www.swift.org/assets/javascripts/new-javas...: 44 KB unused (59%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.swift.org/assets/javascripts/new-javas...: unminified — 3 KB could be saved
Info::
Total unused JavaScript: 44 KB
44 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.swift.org/assets/javascripts/new-javascripts/vendor/anime.iife.min.js75 KB44 KB (59%)✓1st
https://www.swift.org/assets/javascripts/new-javascripts/color-scheme-toggle.js4 KB—✓1st
https://www.swift.org/assets/javascripts/new-javascripts/hero.js9 KB—✗1st
https://www.swift.org/assets/javascripts/new-javascripts/application.js7 KB—✓1st
https://www.swift.org/assets/javascripts/new-javascripts/landing.js2 KB—✓1st
https://developer.apple.com/assets/metrics/scripts/analytics.js83 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

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+
HTTP Caching
max-age=180 (3 minutes)
PASS
max-age=180 (3 minutes)
Info::
Cache-Control header is set
Got: max-age=180, public
Info::
Effective TTL: 3 minutes (max-age=180)
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present
Cache-Control

max-age=180, public

DirectiveValueMeaning
max-age180Cache for 3 minutes
public—Any cache may store this response
Effective TTL: 180 seconds
Network Waterfall
32 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
4% of JavaScript execution is third-party
First-party Third-party 50ms · 0KB · $1/mo
Unattributable
Other
Optional
Execution 50ms
Transfer 0 KB
Monthly Cost $1/mo

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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