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https://python.org

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
92
GRADE
A
FIX
2
REVIEW
2
PASS
8
INFO
2

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

Mobile Desktop
84
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
79
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.

855 ms

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

1.11 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.

0.259

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

855 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.

1.11 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
14
8 PASS 2 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 (499.6 KiB of 499.8 KiB)
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
JS Bundles
10 scripts, 118 KB unused
REVIEW
10 scripts, 118 KB unused
Warning::
https://ajax.googleapis.com/ajax/libs/jqueryui/1.1...: 59 KB unused (89%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://ajax.googleapis.com/ajax/libs/jqueryui/1.1...: 59 KB unused (89%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 118 KB
118 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js66 KB59 KB (89%)✓3rd
https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js0 KB59 KB (89%)✓3rd
https://analytics.python.org/js/script.file-downloads.outbound-links.js2 KB—✓3rd
https://media.ethicalads.io/media/client/v1.4.0/ethicalads.min.js9 KB—✓3rd
https://www.python.org/static/js/libs/modernizr.js5 KB—✓3rd
https://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js33 KB—✓3rd
https://www.python.org/static/js/libs/masonry.pkgd.min.js8 KB—✓3rd
https://www.python.org/static/js/libs/html-includes.js0 KB—✓3rd
https://www.python.org/static/js/main-min.e1f3949ae225.js10 KB—✗3rd
https://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.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

C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
500 KB transferred, 36 requests
PASS
500 KB transferred, 36 requests
Info::
Page weighs 1.2 MB (500 KB transferred)
Info::
36 HTTP requests
Info::
Estimated 0.10 g CO2 per page load
500 KB / 2.4 MB budget
500 KB transferred
36 requests
0.10 g CO2 per page load
CSS 156.0 KiB 31%
Fonts 149.6 KiB 30%
JavaScript 133.3 KiB 27%
Images 28.5 KiB 6%
Other 15.1 KiB 3%
HTML 11.7 KiB 2%
Other 5.3 KiB 1%
Other 298 B 0%
0 2.4 MB 4.9 MB
Under budget
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
2 images, 0 KB saveable
PASS
2 images, 0 KB saveable
Info::
All images are well-optimized
2 images 29 KB
0 oversized -0 KB
2 legacy format
0 missing dimensions CLS risk
A+
JS Execution Cost
150ms total JS execution
PASS
150ms total JS execution
Info::
https://www.python.org/: 91ms CPU time
Info::
https://ajax.googleapis.com/ajax/libs/jquery/1.8.2...: 60ms CPU time
Warning::
Third-party scripts: 150ms (100% of total)

Main Thread Breakdown

Style & Layout 31% Script Evaluation 29% Other 25% Parse HTML & CSS 5% Rendering 5% Script Parsing & Compilation 4%
ScriptTotalScriptingParse/CompileParty
https://www.python.org/91ms1ms0ms3rd
https://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js60ms39ms2ms3rd
A+
Font Loading
6 fonts (150 KB)
PASS
6 fonts (150 KB)
Info::
6 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

6

150 KB total

Render-blocking

0

of 6

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 500 ms 1.0 s FCP 855 ms LCP 1.1 shttps://www.python.org/static/fonts/SourceSansPro-Regular-webfont.fd0d51605201.woffSourceSansPro-Regular-w... https://www.python.org/static/fonts/SourceSansPro-Regular-webfont.fd0d51605201.woff — 25.9 KiB — 0 ms — font-display: swapdata:application/x-font-woff;charset=utf-8;base64,d09GRgABAAAAADDwAAsAAAAAMKQAAQAAAAAAAAAAAAAAAAAAA…x-font-woff;charset=utf... data:application/x-font-woff;charset=utf-8;base64,d09GRgABAAAAADDwAAsAAAAAMKQAAQAAAAAAAAAAAAAAAAAAA… — 12.2 KiB — 0 ms — font-display: swaphttps://www.python.org/static/fonts/FluxRegular.f5549a4fe75f.woffFluxRegular.f5549a4fe75... https://www.python.org/static/fonts/FluxRegular.f5549a4fe75f.woff — 29.4 KiB — 0 ms — font-display: swaphttps://www.python.org/static/fonts/SourceSansPro-Bold-webfont.be855452e565.woffSourceSansPro-Bold-webf... https://www.python.org/static/fonts/SourceSansPro-Bold-webfont.be855452e565.woff — 25.9 KiB — 0 ms — font-display: swaphttps://www.python.org/static/fonts/SourceSansPro-It-webfont.1aa29ac0f190.woffSourceSansPro-It-webfon... https://www.python.org/static/fonts/SourceSansPro-It-webfont.1aa29ac0f190.woff — 27.5 KiB — 0 ms — font-display: swaphttps://www.python.org/static/fonts/FluxBold.3fd71a747d5c.woffFluxBold.3fd71a747d5c.woff https://www.python.org/static/fonts/FluxBold.3fd71a747d5c.woff — 28.6 KiB — 0 ms — font-display: swap
SourceSansPro-Regular-w... woff swap
Size 26 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
x-font-woff;charset=utf... woff swap
Size 12 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
FluxRegular.f5549a4fe75... woff swap
Size 29 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
SourceSansPro-Bold-webf... woff swap
Size 26 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
SourceSansPro-It-webfon... woff swap
Size 27 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
FluxBold.3fd71a747d5c.woff woff swap
Size 29 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
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 ~45 KB and ~90 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
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
Network Waterfall
36 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
100% of JavaScript execution is third-party
First-party Third-party 150ms · 12KB · €2/mo
www.python.org
Other
Optional
Execution 91ms
Transfer 12 KB
Monthly Cost €1/mo
ajax.googleapis.com
Other
Optional
Execution 60ms
Transfer 0 KB
Monthly Cost €1/mo

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

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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