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Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
91
GRADE
A
FIX
2
REVIEW
2
PASS
11
INFO
2

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

Mobile Desktop
93
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
90
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.

1.91 s

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

2.80 s

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

113 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.

2.22 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.

4.15 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
11 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 (617.4 KiB of 617.8 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
Image Optimization
7 images, 0 KB saveable
REVIEW
7 images, 0 KB saveable
Warning::
https://www.sphinx-doc.org/en/master/_static/sphin... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.sphinx-doc.org/en/master/_images/pytho... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.sphinx-doc.org/en/master/_images/linux... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.sphinx-doc.org/en/master/_images/jupyt... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
7 images 450 KB
0 oversized -0 KB
1 legacy format
4 missing dimensions CLS risk

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

B
JS Execution Cost
883ms total JS execution
REVIEW
883ms total JS execution
Warning::
https://www.sphinx-doc.org/_/static/javascript/rea...: 417ms CPU time
Warning::
https://www.sphinx-doc.org/en/master/: 279ms CPU time
Info::
Unattributable: 187ms CPU time
Warning::
Third-party scripts: 883ms (100% of total)

Main Thread Breakdown

Script Evaluation 38% Other 24% Style & Layout 24% Script Parsing & Compilation 5% Rendering 4%
ScriptTotalScriptingParse/CompileParty
https://www.sphinx-doc.org/_/static/javascript/readthedocs-addons.js417ms325ms42ms3rd
https://www.sphinx-doc.org/en/master/279ms5ms1ms3rd
Unattributable187ms5ms0ms3rd
A+
Page Weight Budget
618 KB transferred, 21 requests
PASS
618 KB transferred, 21 requests
Info::
Page weighs 1024 KB (618 KB transferred)
Info::
21 HTTP requests
Info::
Estimated 0.13 g CO2 per page load
618 KB / 2.4 MB budget
618 KB transferred
21 requests
0.13 g CO2 per page load
Images 450.0 KiB 73%
JavaScript 139.2 KiB 23%
CSS 13.8 KiB 2%
HTML 7.1 KiB 1%
Other 4.1 KiB 1%
Other 3.6 KiB 1%
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+
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
4 scripts, 49 KB unused
PASS
4 scripts, 49 KB unused
Warning::
https://www.sphinx-doc.org/_/static/javascript/rea...: 49 KB unused (37%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 49 KB
49 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.sphinx-doc.org/_/static/javascript/readthedocs-addons.js132 KB49 KB (37%)✓3rd
https://www.sphinx-doc.org/en/master/_static/documentation_options.js?v=7ac69e551 KB—✓3rd
https://www.sphinx-doc.org/en/master/_static/doctools.js?v=fd6eb6e63 KB—✓3rd
https://www.sphinx-doc.org/en/master/_static/sphinx_highlight.js?v=6ffebe343 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
Page Weight Inventory
21 resources · 618 KB · 49 KB savings available
PASS
21 resources · 618 KB · 49 KB savings available
Info::
Within 1MB page-weight target
Got: 618 KB
Warning::
20 third-party resources (100% of weight)
Info::
1 resources over 200KB
21 resources · 617.8 KiB · 20 third-party Within 1MB page-weight target
Image 73% · 452.7 KiB
JavaScript 23% · 139.2 KiB
CSS 2% · 13.8 KiB
Document 1% · 8.1 KiB
Other 1% · 3.9 KiB

~48.8 KiB of savings available

Remove unused JavaScript: 48.8 KiB
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
21 requests over 897ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s 2.5 s FCP 1.9 s LCP 2.8 shttps://sphinx-doc.org// https://sphinx-doc.org/ — 301 — 376 B — 61 ms — h2https://www.sphinx-doc.org/www.sphinx-doc.org/ https://www.sphinx-doc.org/ — 302 — 1.0 KiB — 268 ms — h2https://www.sphinx-doc.org/en/master/www.sphinx-doc.org/en/master/ https://www.sphinx-doc.org/en/master/ — 200 — 7.1 KiB — 54 ms — h2https://www.sphinx-doc.org/en/master/_static/pygments.css?v=b86133f3www.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/pygments.css?v=b86133f3 — 200 — 2.1 KiB — 47 ms — h3https://www.sphinx-doc.org/en/master/_static/basic.css?v=29da98fawww.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/basic.css?v=29da98fa — 200 — 4.5 KiB — 57 ms — h3https://www.sphinx-doc.org/en/master/_static/graphviz.css?v=4ae1632dwww.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/graphviz.css?v=4ae1632d — 200 — 1.1 KiB — 42 ms — h3https://www.sphinx-doc.org/en/master/_static/sphinx13.css?v=ba1752c5www.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/sphinx13.css?v=ba1752c5 — 200 — 6.2 KiB — 48 ms — h3https://www.sphinx-doc.org/en/master/_static/documentation_options.js?v=7ac69e55www.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/documentation_options.js?v=7ac69e55 — 200 — 1.2 KiB — 46 ms — h3https://www.sphinx-doc.org/en/master/_static/doctools.js?v=fd6eb6e6www.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/doctools.js?v=fd6eb6e6 — 200 — 2.6 KiB — 33 ms — h3https://www.sphinx-doc.org/en/master/_static/sphinx_highlight.js?v=6ffebe34www.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/sphinx_highlight.js?v=6ffebe34 — 200 — 3.1 KiB — 59 ms — h3https://www.sphinx-doc.org/en/master/_static/sphinx-logo.svgwww.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/sphinx-logo.svg — 200 — 1.5 KiB — 46 ms — h3https://www.sphinx-doc.org/en/master/_images/python-logo.pngwww.sphinx-doc.org/en/master/_image... https://www.sphinx-doc.org/en/master/_images/python-logo.png — 200 — 57.0 KiB — 183 ms — h3https://www.sphinx-doc.org/en/master/_images/linux-logo.pngwww.sphinx-doc.org/en/master/_image... https://www.sphinx-doc.org/en/master/_images/linux-logo.png — 200 — 349.4 KiB — 195 ms — h3https://www.sphinx-doc.org/en/master/_images/jupyter-logo.pngwww.sphinx-doc.org/en/master/_image... https://www.sphinx-doc.org/en/master/_images/jupyter-logo.png — 200 — 42.1 KiB — 181 ms — h3https://www.sphinx-doc.org/_/static/javascript/readthedocs-addons.jswww.sphinx-doc.org/_/static/javascr... https://www.sphinx-doc.org/_/static/javascript/readthedocs-addons.js — 200 — 132.3 KiB — 73 ms — h3data:image/svg+xml;charset=utf-8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path …www.w3.org/2000/svg" viewBox="0 0 2... data:image/svg+xml;charset=utf-8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path … — 200 — 0 B — 0 ms — datahttps://www.sphinx-doc.org/_/addons/?client-version=0.49.0&api-version=1&project-slug=sphinx&version-slug=masterwww.sphinx-doc.org/_/addons/?client... https://www.sphinx-doc.org/_/addons/?client-version=0.49.0&api-version=1&project-slug=sphinx&version-slug=master — 200 — 2.9 KiB — 53 ms — h3https://www.sphinx-doc.org/en/master/_static/favicon.svgwww.sphinx-doc.org/en/master/_stati... https://www.sphinx-doc.org/en/master/_static/favicon.svg — 200 — 2.7 KiB — 26 ms — h3https://www.sphinx-doc.org/_/api/v2/analytics/?project=sphinx&version=master&absolute_uri=https%3A%2F%2Fwww.sphinx-doc.org%2Fen%2Fmaster%2F&status=200www.sphinx-doc.org/_/api/v2/analyti... https://www.sphinx-doc.org/_/api/v2/analytics/?project=sphinx&version=master&absolute_uri=https%3A%2F%2Fwww.sphinx-doc.org%2Fen%2Fmaster%2F&status=200 — 204 — 696 B — 212 ms — h3data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiIHN0YW5kYWxvbmU9Im5vIj8+C…data:image/svg+xml;base64,PD94bWwgd... data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiIHN0YW5kYWxvbmU9Im5vIj8+C… — 200 — 0 B — 0 ms — datadata:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPHN2ZyB2ZXJzaW9uPSIxL…data:image/svg+xml;base64,PD94bWwgd... data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPHN2ZyB2ZXJzaW9uPSIxL… — 200 — 0 B — 0 ms — data
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 883ms · 139KB · $12/mo
www.sphinx-doc.org
Other
Costly
Execution 417ms
Transfer 132 KB
Unused 37%
Monthly Cost $6/mo
www.sphinx-doc.org
Other
Costly
Execution 279ms
Transfer 7 KB
Monthly Cost $4/mo
Unattributable
Other
Optional
Execution 187ms
Transfer 0 KB
Monthly Cost $2/mo

These scripts may cost more than they're worth

  • www.sphinx-doc.org adds 417ms and costs ~$6/month
  • www.sphinx-doc.org adds 279ms and costs ~$4/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

www.sphinx-doc.org takes 417ms 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

www.sphinx-doc.org takes 279ms 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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