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https://leeds.ac.uk

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
86
GRADE
B
FIX
2
REVIEW
4
PASS
7
INFO
2

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

Mobile Desktop
62
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.
96
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
100
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.

1.71 s

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

2.37 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.

0.287

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

2.28 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.

2.38 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
15
7 PASS 4 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 (1.4 MiB of 1.4 MiB)
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
Page Weight Budget
1.4 MB transferred, 32 requests
REVIEW
1.4 MB transferred, 32 requests
Info::
Page weighs 2.2 MB (1.4 MB transferred)
Warning::
Images are 1.1 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 1.1 MB
Info::
32 HTTP requests
Info::
Estimated 0.29 g CO2 per page load
1.4 MB / 2.4 MB budget
1.4 MB transferred
32 requests
0.29 g CO2 per page load
Images 1.1 MiB 79%
JavaScript 114.0 KiB 8%
Fonts 95.0 KiB 7%
CSS 63.7 KiB 4%
Other 15.2 KiB 1%
HTML 15.0 KiB 1%
Other 760 B 0%
Other 0 B 0%
0 2.4 MB 4.9 MB
Under 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

C
Image Optimization
Action
16 images, 0 KB saveable
REVIEW
16 images, 0 KB saveable
Warning::
https://www.leeds.ac.uk/images/resized/565x757-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/450x300-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/565x757-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/567x707-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/450x300-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/450x300-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/450x300-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/565x757-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/450x300-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.leeds.ac.uk/images/resized/450x300-0-0... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
16 images 1.1 MB
0 oversized -0 KB
15 legacy format
10 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

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

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

C
Page Weight Inventory
Action
32 resources · 1.4 MB · 45 KB savings available
REVIEW
32 resources · 1.4 MB · 45 KB savings available
Warning::
Page weight 394 KB over 1MB target
Got: 1.4 MB Expected: ≤ 1 MB
Warning::
31 third-party resources (100% of weight)
Info::
1 resources over 200KB
32 resources · 1.4 MiB · 31 third-party 393.8 KiB over 1MB target
Image 80% · 1.1 MiB
JavaScript 8% · 114.0 KiB
Font 7% · 95.0 KiB
CSS 4% · 63.7 KiB
Document 1% · 15.2 KiB
Other 0% · 760 B

~44.8 KiB of savings available

Remove unused JavaScript: 44.8 KiB
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

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+
JS Execution Cost
464ms total JS execution
PASS
464ms total JS execution
Info::
https://www.leeds.ac.uk/: 202ms CPU time
Info::
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/...: 148ms CPU time
Info::
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/...: 61ms CPU time
Info::
Unattributable: 53ms CPU time
Warning::
Third-party scripts: 464ms (100% of total)

Main Thread Breakdown

Other 33% Style & Layout 32% Script Evaluation 15% Rendering 12% Parse HTML & CSS 4%
ScriptTotalScriptingParse/CompileParty
https://www.leeds.ac.uk/202ms2ms0ms3rd
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/bundle.js148ms39ms8ms3rd
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/uol-cookie-control.js?version=0.161ms27ms4ms3rd
Unattributable53ms2ms0ms3rd
A+
Font Loading
4 fonts (95 KB)
PASS
4 fonts (95 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

95 KB total

Render-blocking

0

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 500 ms 1.0 s 1.5 s 2.0 s FCP 1.7 s LCP 2.4 shttps://use.typekit.net/af/442215/000000000000000000010b5a/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/442215/000000000000000000010b5a/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 23.5 KiB — 18 ms — font-display: swaphttps://use.typekit.net/af/cef9f3/000000000000000000010b5e/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3l https://use.typekit.net/af/cef9f3/000000000000000000010b5e/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3 — 23.9 KiB — 25 ms — font-display: swaphttps://use.typekit.net/af/80e9a7/000000000000000077359fce/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n9&v=3l https://use.typekit.net/af/80e9a7/000000000000000077359fce/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n9&v=3 — 24.7 KiB — 21 ms — font-display: swaphttps://use.typekit.net/af/8dd886/000000000000000000010b5c/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3l https://use.typekit.net/af/8dd886/000000000000000000010b5c/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 22.9 KiB — 25 ms — font-display: swap
l woff2 swap
Size 23 KB
Load time 18 ms
Start 2.3 s
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 24 KB
Load time 25 ms
Start 2.3 s
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 25 KB
Load time 21 ms
Start 2.3 s
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 23 KB
Load time 25 ms
Start 2.3 s
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+
JS Bundles
4 scripts, 45 KB unused
PASS
4 scripts, 45 KB unused
Warning::
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/...: 45 KB unused (64%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 45 KB
45 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/bundle.js70 KB45 KB (64%)✓3rd
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/modernizr-custom.js3 KB—✓3rd
https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/uol-cookie-control.js?version=0.140 KB—✓3rd
https://production2.leeds.ac.uk/jaducdn/site/javascript/forms.min.js?v=17761580061 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
Network Waterfall
32 requests over 2971ms
INFO
0 ms 1.0 s 2.0 s 3.0 s FCP 1.7 s LCP 2.4 shttps://leeds.ac.uk// https://leeds.ac.uk/ — 302 — 190 B — 807 ms — h2https://www.leeds.ac.uk/www.leeds.ac.uk/ https://www.leeds.ac.uk/ — 200 — 15.0 KiB — 745 ms — h2https://use.typekit.net/xpd0xwa.cssuse.typekit.net/xpd0xwa.css https://use.typekit.net/xpd0xwa.css — 200 — 1.0 KiB — 14 ms — h2https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/css/style.cssjaducdn.leeds.ac.uk/uol-ds/1.0.20/c... https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/css/style.css — 200 — 62.5 KiB — 577 ms — h2https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/modernizr-custom.jsjaducdn.leeds.ac.uk/uol-ds/1.0.20/s... https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/modernizr-custom.js — 200 — 3.0 KiB — 385 ms — h2https://www.leeds.ac.uk/images/resized/334x330-0-0-1-80-Untitled_design__12__2.pngwww.leeds.ac.uk/images/resized/334x... https://www.leeds.ac.uk/images/resized/334x330-0-0-1-80-Untitled_design__12__2.png — 200 — 22.7 KiB — 196 ms — h2https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/bundle.jsjaducdn.leeds.ac.uk/uol-ds/1.0.20/s... https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/bundle.js — 200 — 69.9 KiB — 567 ms — h2https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/favicons/site.webmanifestjaducdn.leeds.ac.uk/uol-ds/1.0.20/f... https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/favicons/site.webmanifest — -1 — 0 B — 1.1 s — https://p.typekit.net/p.css?s=1&k=xpd0xwa&ht=tk&f=10954.13458.13460.13470.13474&a=2901748&app=typekit&e=cssp.typekit.net/p.css?s=1&k=xpd0xwa&h... https://p.typekit.net/p.css?s=1&k=xpd0xwa&ht=tk&f=10954.13458.13460.13470.13474&a=2901748&app=typekit&e=css — 200 — 172 B — 21 ms — h2https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/uol-cookie-control.js?version=0.1jaducdn.leeds.ac.uk/uol-ds/1.0.20/s... https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/uol-cookie-control.js?version=0.1 — 200 — 40.3 KiB — 378 ms — h2https://production2.leeds.ac.uk/jaducdn/site/javascript/forms.min.js?v=1776158006production2.leeds.ac.uk/jaducdn/sit... https://production2.leeds.ac.uk/jaducdn/site/javascript/forms.min.js?v=1776158006 — 200 — 822 B — 457 ms — h2https://www.leeds.ac.uk/www.leeds.ac.uk/ https://www.leeds.ac.uk/ — -1 — 0 B — 139 ms — https://www.leeds.ac.uk/images/resized/1600x400-0-0-1-80-Untitled_design__21__2.pngwww.leeds.ac.uk/images/resized/1600... https://www.leeds.ac.uk/images/resized/1600x400-0-0-1-80-Untitled_design__21__2.png — 200 — 211.4 KiB — 394 ms — h2https://www.leeds.ac.uk/images/resized/1600x400-0-0-1-80-Untitled_design__25__2.pngwww.leeds.ac.uk/images/resized/1600... https://www.leeds.ac.uk/images/resized/1600x400-0-0-1-80-Untitled_design__25__2.png — 200 — 121.5 KiB — 378 ms — h2https://www.leeds.ac.uk/images/resized/1600x400-0-0-1-80-banner_4_1600x400.pngwww.leeds.ac.uk/images/resized/1600... https://www.leeds.ac.uk/images/resized/1600x400-0-0-1-80-banner_4_1600x400.png — 200 — 186.2 KiB — 395 ms — h2https://www.youtube.com/oembed?url=http%3A//www.youtube.com/watch?v%3DMfVGC7Bq_ZA&format=jsonwww.youtube.com/oembed?url=http%3A/... https://www.youtube.com/oembed?url=http%3A//www.youtube.com/watch?v%3DMfVGC7Bq_ZA&format=json — 200 — 760 B — 256 ms — h2https://i.ytimg.com/vi/MfVGC7Bq_ZA/maxresdefault.jpgi.ytimg.com/vi/MfVGC7Bq_ZA/maxresde... https://i.ytimg.com/vi/MfVGC7Bq_ZA/maxresdefault.jpg — 200 — 123.5 KiB — 77 ms — h2https://use.typekit.net/af/442215/000000000000000000010b5a/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3use.typekit.net/af/442215/000000000... https://use.typekit.net/af/442215/000000000000000000010b5a/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 200 — 23.5 KiB — 18 ms — h2https://use.typekit.net/af/cef9f3/000000000000000000010b5e/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3use.typekit.net/af/cef9f3/000000000... https://use.typekit.net/af/cef9f3/000000000000000000010b5e/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n6&v=3 — 200 — 23.9 KiB — 25 ms — h2https://use.typekit.net/af/80e9a7/000000000000000077359fce/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n9&v=3use.typekit.net/af/80e9a7/000000000... https://use.typekit.net/af/80e9a7/000000000000000077359fce/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n9&v=3 — 200 — 24.7 KiB — 21 ms — h2https://use.typekit.net/af/8dd886/000000000000000000010b5c/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3use.typekit.net/af/8dd886/000000000... https://use.typekit.net/af/8dd886/000000000000000000010b5c/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 200 — 22.9 KiB — 25 ms — h2https://www.leeds.ac.uk/images/resized/565x757-0-0-1-80-Untitled_design__10_.pngwww.leeds.ac.uk/images/resized/565x... https://www.leeds.ac.uk/images/resized/565x757-0-0-1-80-Untitled_design__10_.png — 200 — 52.5 KiB — 291 ms — h2https://www.leeds.ac.uk/images/resized/565x757-0-0-1-80-Untitled_design__9__1.pngwww.leeds.ac.uk/images/resized/565x... https://www.leeds.ac.uk/images/resized/565x757-0-0-1-80-Untitled_design__9__1.png — 200 — 55.7 KiB — 295 ms — h2https://www.leeds.ac.uk/images/resized/567x707-0-0-1-80-Untitled_design__34__3.pngwww.leeds.ac.uk/images/resized/567x... https://www.leeds.ac.uk/images/resized/567x707-0-0-1-80-Untitled_design__34__3.png — 200 — 57.9 KiB — 285 ms — h2https://www.leeds.ac.uk/images/resized/565x757-0-0-1-80-Untitled_design__11__2.pngwww.leeds.ac.uk/images/resized/565x... https://www.leeds.ac.uk/images/resized/565x757-0-0-1-80-Untitled_design__11__2.png — 200 — 67.7 KiB — 199 ms — h2https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Untitled_design__52__2.pngwww.leeds.ac.uk/images/resized/450x... https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Untitled_design__52__2.png — 200 — 49.2 KiB — 198 ms — h2https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-QEP_450x300.jpgwww.leeds.ac.uk/images/resized/450x... https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-QEP_450x300.jpg — 200 — 30.7 KiB — 199 ms — h2https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Everest_panorama_450x300.jpgwww.leeds.ac.uk/images/resized/450x... https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Everest_panorama_450x300.jpg — 200 — 43.1 KiB — 205 ms — h2https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Untitled_design__50_.pngwww.leeds.ac.uk/images/resized/450x... https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Untitled_design__50_.png — 200 — 31.5 KiB — 201 ms — h2https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Untitled_design__52__1.pngwww.leeds.ac.uk/images/resized/450x... https://www.leeds.ac.uk/images/resized/450x300-0-0-1-80-Untitled_design__52__1.png — 200 — 31.8 KiB — 207 ms — h2
0 ms 1.0 s 2.0 s 3.0 s FCP 1.7 s LCP 2.4 shttps://leeds.ac.uk// https://leeds.ac.uk/ — 302 — 190 B — 807 ms — h2https://www.leeds.ac.uk/www.leeds.ac.uk/ https://www.leeds.ac.uk/ — 200 — 15.0 KiB — 745 ms — h2https://use.typekit.net/xpd0xwa.cssuse.typekit.net/xpd0xwa.css https://use.typekit.net/xpd0xwa.css — 200 — 1.0 KiB — 14 ms — h2https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/css/style.cssjaducdn.leeds.ac.uk/uol-ds/1.0.20/c... https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/css/style.css — 200 — 62.5 KiB — 577 ms — h2https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/modernizr-custom.jsjaducdn.leeds.ac.uk/uol-ds/1.0.20/s... https://jaducdn.leeds.ac.uk/uol-ds/1.0.20/scripts/modernizr-custom.js — 200 — 3.0 KiB — 385 ms — h2https://www.leeds.ac.uk/images/resized/334x330-0-0-1-80-Untitled_design__12__2.pngwww.leeds.ac.uk/images/resized/334x... https://www.leeds.ac.uk/images/resized/334x330-0-0-1-80-Untitled_design__12__2.png — 200 — 22.7 KiB — 196 ms — 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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 464ms · 110KB · £5/mo
www.leeds.ac.uk
Other
Costly
Execution 202ms
Transfer 0 KB
Monthly Cost £2/mo
jaducdn.leeds.ac.uk
Other
Optional
Execution 148ms
Transfer 70 KB
Unused 64%
Monthly Cost £2/mo
jaducdn.leeds.ac.uk
Other
Optional
Execution 61ms
Transfer 40 KB
Monthly Cost £1/mo
Unattributable
Other
Optional
Execution 53ms
Transfer 0 KB
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • www.leeds.ac.uk adds 202ms and costs ~£2/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.leeds.ac.uk takes 202ms 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

64% of jaducdn.leeds.ac.uk's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

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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