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

Performance

100

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.

1.17 s

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

2.27 s

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

1 ms

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

0.009

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

1.52 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.

2.90 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

5 PASS 5 REVIEW 3 FIX

Page Weight Budget

Action

6.0 MB transferred, 171 requests

FIX

6.0 MB transferred, 171 requests

Page weighs 9.9 MB (6.0 MB transferred)

Images are 3.3 MB — compress or use modern formats

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Got: 3.3 MB

Fonts are 2.1 MB — consider subsetting or using system fonts

Subset fonts to include only used characters, or switch to system font stacks.

Got: 2.1 MB

JavaScript is 519 KB — consider code splitting or lazy loading

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Got: 519 KB

171 HTTP requests — consider bundling or reducing

Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.

Estimated 1.3 g CO2 per page load

6.0 MB transferred

171 requests

1.3 g CO2 per page load

Images 3.3 MiB 55%

Fonts 2.1 MiB 34%

JavaScript 518.9 KiB 8%

CSS 114.8 KiB 2%

HTML 24.2 KiB 0%

Other 3.8 KiB 0%

Other 558 B 0%

Other 549 B 0%

0 2.4 MB 4.9 MB

Over budget

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Why this matters

Image bandwidth is high — modern formats (WebP/AVIF) and resizing typically cut it 50%+.

Source: web.dev

Subset fonts to include only used characters, or switch to system font stacks.

Why this matters

Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).

Source: web.dev font loading

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

Third-Party Impact

Action

82% third-party, 0 ms blocking

FIX

82% third-party, 0 ms blocking

Third-party code accounts for 82% of page weight (5.0 MiB of 6.0 MiB)

Third-party blocking time is low (0 ms)

18%

82%

First-party Third-party

Page Weight Inventory

Action

171 resources · 6.0 MB · 146 KB savings available

FIX

171 resources · 6.0 MB · 146 KB savings available

Page weight 5.0 MB over 1MB target

Got: 6.0 MB Expected: ≤ 1 MB

~146 KB of savings available

66 third-party resources (82% of weight)

8 resources over 200KB

171 resources · 6.0 MiB · 66 third-party 5.0 MiB over 1MB target

Image 55% · 3.3 MiB

Font 34% · 2.1 MiB

JavaScript 8% · 518.9 KiB

CSS 2% · 114.8 KiB

Document 0% · 24.2 KiB

Other 0% · 1.4 KiB

~146.4 KiB of savings available

Remove unused JavaScript: 146.4 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

171 resources			6.0 MiB

Image Optimization

25 images, 0 KB saveable

REVIEW

25 images, 0 KB saveable

All images are well-optimized

25 images 3.3 MB

0 oversized -0 KB

4 legacy format

0 missing dimensions CLS risk

JS Execution Cost

Action

1189ms total JS execution

REVIEW

1189ms total JS execution

https://www.keio.ac.jp/ja/: 688ms CPU time

https://www.keio.ac.jp/_astro/client.B9bUpm8d.js: 281ms CPU time

Unattributable: 157ms CPU time

https://www.googletagmanager.com/gtag/js?id=G-BYN8...: 63ms CPU time

Third-party scripts: 220ms (18% of total)

Main Thread Breakdown

Style & Layout 48% Script Evaluation 24% Other 19% Rendering 5%

Script	Total	Scripting	Parse/Compile	Party
https://www.keio.ac.jp/ja/	688ms	8ms	1ms	1st
https://www.keio.ac.jp/_astro/client.B9bUpm8d.js	281ms	212ms	0ms	1st
Unattributable	157ms	8ms	0ms	3rd
https://www.googletagmanager.com/gtag/js?id=G-BYN8CM9PTN&cx=c&gtm=4e64h1	63ms	52ms	9ms	3rd

JS Bundles

85 scripts, 146 KB unused

REVIEW

85 scripts, 146 KB unused

https://www.googletagmanager.com/gtag/js?id=G-BYN8...: 65 KB unused (41%)

Consider code splitting or tree shaking to reduce unused code.

https://www.googletagmanager.com/gtm.js?id=GTM-N74...: 61 KB unused (49%)

Consider code splitting or tree shaking to reduce unused code.

https://www.keio.ac.jp/_astro/client.B9bUpm8d.js: 21 KB unused (38%)

Consider code splitting or tree shaking to reduce unused code.

Total unused JavaScript: 146 KB

146 KB unused JavaScript

Downloaded but never executed on this page.

Script	Size	Unused	Minified	Party
https://www.googletagmanager.com/gtag/js?id=G-BYN8CM9PTN&cx=c&gtm=4e64h1	157 KB	65 KB (41%)	✓	3rd
https://www.googletagmanager.com/gtm.js?id=GTM-N74PD224	125 KB	61 KB (49%)	✓	3rd
https://www.keio.ac.jp/_astro/client.B9bUpm8d.js	55 KB	21 KB (38%)	✓	1st
https://recommend.www-prd.keio.ac.jp/js.recommend/tlab_v4.js	4 KB	—	✓	3rd
https://www.keio.ac.jp/_astro/index.astro_astro_type_script_index_0_lang.C8-l46be.js	1 KB	—	✓	1st
https://www.keio.ac.jp/_astro/index.astro_astro_type_script_index_0_lang.u9MbvrJb.js	1 KB	—	✓	1st
https://www.keio.ac.jp/_astro/index.astro_astro_type_script_index_0_lang.CxlcUlr_.js	1 KB	—	✓	1st
https://www.keio.ac.jp/_astro/index.astro_astro_type_script_index_0_lang.CT5tfAV9.js	1 KB	—	✓	1st
https://www.keio.ac.jp/_astro/index.astro_astro_type_script_index_0_lang.DAN8Lx6U.js	1 KB	—	✓	1st
https://www.keio.ac.jp/_astro/index.astro_astro_type_script_index_0_lang.D_uX7pEa.js	1 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

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

Green Hosting

Action

Whether the site is served from green-energy infrastructure

REVIEW

Green Hosting

No green hosting detected

HTTP Caching

public, max-age=0, s-maxage=60, stale-while-revalidate=86400, stale-if-error=86400

REVIEW

public, max-age=0, s-maxage=60, stale-while-revalidate=86400, stale-if-error=86400

Cache-Control header is set

Got: public, max-age=0, s-maxage=60, stale-while-revalidate=86400, stale-if-error=86400

CDN TTL: 1 minute (s-maxage=60)

No ETag or Last-Modified header

Conditional requests (304 Not Modified) are not possible without validators.

Cache-Control

public, max-age=0, s-maxage=60, stale-while-revalidate=86400, stale-if-error=86400

Directive	Value	Meaning
public	—	Any cache may store this response
max-age	0	Cache for 0 seconds
s-maxage	60	CDN caches for 1 minute
stale-while-revalidate	86400	Serve stale for 1 day while fetching fresh
stale-if-error	86400

A+

Text Compression

All text resources are compressed

PASS

All text resources are compressed

All text resources are properly compressed.

A+

Font Loading

37 fonts (2131 KB)

PASS

37 fonts (2131 KB)

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

Web fonts

2131 KB total

Render-blocking

of 37

Dominant font-display

swap

Most common across fonts

Font loading timeline

Transfer FOIT (block) FOUT (swap)

5fw3eaa0kr.woff2 woff2 swap

Size 52 KB

Load time 199 ms

Start 895 ms