Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.

SCORE

GRADE

FIX

REVIEW

PASS

INFO

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

Mobile Desktop

100

Performance

Accessibility

100

Best Practices

100

SEO

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

263 ms

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

793 ms

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

6 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.

291 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.

867 ms

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

10 PASS 3 REVIEW

Image Optimization

Action

37 images, 0 KB saveable

REVIEW

37 images, 0 KB saveable

https://jupyter.org/assets/homepage/hublogo.svg is missing width/height — may cause layout shift

Set explicit width and height to prevent CLS.

https://jupyter.org/assets/logos/rectanglelogo-gre... is missing width/height — may cause layout shift

Set explicit width and height to prevent CLS.

37 images 308 KB

0 oversized -0 KB

34 legacy format

2 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

JS Bundles

4 scripts, 73 KB unused

REVIEW

4 scripts, 73 KB unused

https://js.hsforms.net/forms/embed/v2.js: 73 KB unused (39%)

Consider code splitting or tree shaking to reduce unused code.

Total unused JavaScript: 73 KB

73 KB unused JavaScript

Downloaded but never executed on this page.

Script	Size	Unused	Minified	Party
https://js.hsforms.net/forms/embed/v2.js	193 KB	73 KB (39%)	✓	3rd
https://cdn.jsdelivr.net/npm/anchor-js/anchor.min.js	3 KB	—	✓	3rd
https://plausible.io/js/pa-B75UO5--FNXYQSG7GBWkf.js	3 KB	—	✓	3rd
https://jupyter.org/assets/js/bootstrap-native.min.js	13 KB	—	✓	1st

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

Green Hosting

Action

Whether the site is served from green-energy infrastructure

REVIEW

Green Hosting

No green hosting detected

A+

Page Weight Budget

555 KB transferred, 48 requests

PASS

555 KB transferred, 48 requests

Page weighs 1.6 MB (555 KB transferred)

48 HTTP requests

Estimated 0.11 g CO2 per page load

555 KB transferred

48 requests

0.11 g CO2 per page load

Images 308.4 KiB 56%

JavaScript 212.0 KiB 38%

Other 11.6 KiB 2%

CSS 8.1 KiB 1%

Other 6.7 KiB 1%

HTML 6.2 KiB 1%

Fonts 996 B 0%

Other 502 B 0%

0 2.4 MB 4.9 MB

Under budget

Third-Party Impact

38% third-party, 0 ms blocking

PASS

38% third-party, 0 ms blocking

Third-party code accounts for 38% of page weight (208.4 KiB of 554.6 KiB)

Third-party blocking time is low (0 ms)

62%

38%

First-party Third-party

A+

Text Compression

All text resources are compressed

PASS

All text resources are compressed

All text resources are properly compressed.

A+

JS Execution Cost

445ms total JS execution

PASS

445ms total JS execution

Unattributable: 166ms CPU time

https://jupyter.org/: 143ms CPU time

https://js.hsforms.net/forms/embed/v2.js: 136ms CPU time

Third-party scripts: 302ms (68% of total)

Main Thread Breakdown

Other 39% Script Evaluation 27% Style & Layout 19% Parse HTML & CSS 6% Script Parsing & Compilation 5% Rendering 4%

Script	Total	Scripting	Parse/Compile	Party
Unattributable	166ms	3ms	0ms	3rd
https://jupyter.org/	143ms	18ms	1ms	1st
https://js.hsforms.net/forms/embed/v2.js	136ms	91ms	22ms	3rd

A+

Font Loading

1 fonts (1 KB)

PASS

1 fonts (1 KB)

1 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

1 KB total

Render-blocking

of 1

Dominant font-display

swap

Most common across fonts

Font loading timeline

Transfer FOIT (block) FOUT (swap)

a;base64,AAEAAAALAIAAAw... unknown swap

Size 1 KB

Load time 5 ms

Start 305 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

No caching issues found

All static resources have appropriate caching headers.

A+

Critical Rendering Path

No render-blocking resources

PASS

No render-blocking resources

No render-blocking resources detected

A+

Resource Hints

No optimization needed

PASS

No optimization needed

No resource hint issues

A+

Page Weight Inventory

48 resources · 555 KB · 73 KB savings available

PASS

48 resources · 555 KB · 73 KB savings available

Within 1MB page-weight target

Got: 555 KB

~73 KB of savings available

8 third-party resources (38% of weight)

48 resources · 554.6 KiB · 8 third-party Within 1MB page-weight target

Image 58% · 320.1 KiB

JavaScript 38% · 212.0 KiB

CSS 1% · 8.1 KiB

Other 1% · 7.2 KiB

Document 1% · 6.2 KiB

Font 0% · 996 B

~73.1 KiB of savings available

Remove unused JavaScript: 73.1 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

48 resources			554.6 KiB

A+

HTTP Caching

max-age=600 (10 minutes)

PASS

max-age=600 (10 minutes)

Cache-Control header is set

Got: max-age=600

Effective TTL: 10 minutes (max-age=600)

ETag present — enables conditional (304) responses

Last-Modified header present

Cache-Control

max-age=600

Directive	Value	Meaning
max-age	600	Cache for 10 minutes

Effective TTL: 600 seconds

Network Waterfall

48 requests over 483ms

INFO

HTML JavaScript CSS Images Fonts XHR/Fetch Other

Third-Party Script Cost

Per-script blocking time, transfer cost, and cache headers

INFO

68% of JavaScript execution is third-party

First-party Third-party 302ms · 193KB · €3/mo

Script	Category	Execution	Transfer	Unused	Monthly Cost	Verdict
Unattributable Unattributable	Other	166ms	0 KB	—	€2/mo	Optional
js.hsforms.net js.hsforms.net	Other	136ms	193 KB	39%	€1/mo	Optional

Unattributable

Other

Optional

Execution 166ms

Transfer 0 KB

Monthly Cost €2/mo

js.hsforms.net

Other

Optional

Execution 136ms

Transfer 193 KB

Unused 39%

Monthly Cost €1/mo

68% of JavaScript execution time comes from third-party scripts.

Why this matters

Third-party scripts (analytics, ads, social, A/B testing) often dominate execution time — every one is a perf-and-privacy tax.

Learn more ▾

Each third-party script is a black box: you don't control when it loads, what it executes, or how much it grows. They often account for a major share of total blocking time on average sites (HTTP Archive's Web Almanac documents the trend). Audit which ones you actually need, defer the rest, and use facade patterns (lite-youtube, lite-vimeo) for embedded media.

Source: web.dev / HTTP Archive Web Almanac

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.