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https://cardiff.ac.uk

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
80
GRADE
B
FIX
4
REVIEW
3
PASS
8
INFO
2

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

Mobile Desktop
36
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
93
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.
91
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.

5.67 s

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

13.04 s

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

1.10 s

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

0.006

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

6.67 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.

13.13 s

Page Load Progression

593 ms
1.2 s
1.8 s
2.4 s
3.0 s
3.6 s
4.2 s
4.7 s
Checks
17
8 PASS 3 REVIEW 4 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 (1.8 MiB of 1.8 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Execution Cost
Action
3139ms total JS execution
FIX
3139ms total JS execution
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-WFW...: 753ms CPU time
Warning::
https://www.cardiff.ac.uk/: 742ms CPU time
Warning::
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/main...: 554ms CPU time
Warning::
Unattributable: 415ms CPU time
Warning::
https://www.googletagmanager.com/gtag/js?id=DC-142...: 318ms CPU time
Warning::
Third-party scripts: 3139ms (100% of total)

Main Thread Breakdown

Script Evaluation 39% Style & Layout 24% Other 20% Script Parsing & Compilation 9% Parse HTML & CSS 5% Rendering 3%
ScriptTotalScriptingParse/CompileParty
https://www.googletagmanager.com/gtm.js?id=GTM-WFW24X753ms561ms118ms3rd
https://www.cardiff.ac.uk/742ms38ms4ms3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/main.js554ms194ms15ms3rd
Unattributable415ms22ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=DC-14284772&cx=c&gtm=4e64k0318ms257ms60ms3rd
https://widget.geckoengage.com/embed211ms135ms45ms3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/6671.js87ms25ms1ms3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/css/main.css59ms0ms0ms3rd
D
Page Weight Inventory
Action
44 resources · 1.8 MB · 174 KB savings available
FIX
44 resources · 1.8 MB · 174 KB savings available
Warning::
Page weight 834 KB over 1MB target
Got: 1.8 MB Expected: ≤ 1 MB
Info::
~174 KB of savings available
Warning::
43 third-party resources (100% of weight)
Info::
1 resources over 200KB
44 resources · 1.8 MiB · 43 third-party 834.2 KiB over 1MB target
JavaScript 37% · 696.5 KiB
Font 25% · 459.1 KiB
Image 22% · 417.4 KiB
CSS 14% · 252.0 KiB
Document 2% · 28.5 KiB
Other 0% · 4.7 KiB

~174.4 KiB of savings available

Remove unused JavaScript: 174.4 KiB
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.

C
Page Weight Budget
Action
1.8 MB transferred, 44 requests
REVIEW
1.8 MB transferred, 44 requests
Info::
Page weighs 3.3 MB (1.8 MB transferred)
Warning::
JavaScript is 697 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 697 KB
Info::
Fonts are 459 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 459 KB
Info::
CSS is 252 KB — consider purging unused styles
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
Got: 252 KB
Info::
44 HTTP requests
Info::
Estimated 0.38 g CO2 per page load
1.8 MB / 2.4 MB budget
1.8 MB transferred
44 requests
0.38 g CO2 per page load
JavaScript 696.5 KiB 37%
Fonts 459.1 KiB 25%
Images 401.1 KiB 22%
CSS 252.0 KiB 14%
HTML 28.0 KiB 2%
Other 16.9 KiB 1%
Other 4.6 KiB 0%
0 2.4 MB 4.9 MB
Approaching limit

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

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

Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.

Why this matters

CSS bundle is large — purge unused styles (PurgeCSS, Tailwind JIT) to reduce CSS payload.

Source: web.dev

C
JS Bundles
Action
9 scripts, 174 KB unused
REVIEW
9 scripts, 174 KB unused
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-WFW...: 78 KB unused (41%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=DC-142...: 62 KB unused (48%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/vend...: 35 KB unused (69%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 174 KB
174 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtm.js?id=GTM-WFW24X192 KB78 KB (41%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-14284772&cx=c&gtm=4e64k0129 KB62 KB (48%)✓3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/vendor.js51 KB35 KB (69%)✓3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/runtime.js2 KB—✓3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/main.js27 KB—✓3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/733.js2 KB—✓3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/6671.js2 KB—✓3rd
https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/55.js4 KB—✓3rd
https://widget.geckoengage.com/embed/286 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

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+
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
15 images, 0 KB saveable
PASS
15 images, 0 KB saveable
Warning::
https://cardiff.imgix.net/__data/assets/image/0008... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cardiff.imgix.net/__data/assets/image/0006... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cardiff.imgix.net/__data/assets/image/0007... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cardiff.imgix.net/__data/assets/image/0005... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cardiff.imgix.net/__data/assets/image/0006... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cardiff.imgix.net/__data/assets/image/0010... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://cardiff.imgix.net/__data/assets/image/0009... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
15 images 401 KB
0 oversized -0 KB
0 legacy format
8 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

A+
Font Loading
7 fonts (459 KB)
PASS
7 fonts (459 KB)
Info::
7 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

7

459 KB total

Render-blocking

0

of 7

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s FCP 5.7 s LCP 13.0 shttps://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Med.woff2Marr-Sans-Med.woff2 https://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Med.woff2 — 25.9 KiB — 24 ms — font-display: swaphttps://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Bold.woff2Marr-Sans-Bold.woff2 https://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Bold.woff2 — 25.1 KiB — 26 ms — font-display: swaphttps://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Darby-Rg.woff2Darby-Rg.woff2 https://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Darby-Rg.woff2 — 44.9 KiB — 25 ms — font-display: swaphttps://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Rg.woff2Marr-Sans-Rg.woff2 https://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Rg.woff2 — 24.4 KiB — 23 ms — font-display: swaphttps://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Ultra.woff2Marr-Sans-Ultra.woff2 https://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Ultra.woff2 — 23.7 KiB — 24 ms — font-display: swaphttps://widget.geckoengage.com/embed/static/media/fa-solid-900.54dfc8f5.woff2fa-solid-900.54dfc8f5.w... https://widget.geckoengage.com/embed/static/media/fa-solid-900.54dfc8f5.woff2 — 134.5 KiB — 22 ms — font-display: swaphttps://widget.geckoengage.com/embed/static/media/fa-light-300.d3271a56.woff2fa-light-300.d3271a56.w... https://widget.geckoengage.com/embed/static/media/fa-light-300.d3271a56.woff2 — 180.5 KiB — 25 ms — font-display: swap
Marr-Sans-Med.woff2 woff2 swap
Size 26 KB
Load time 24 ms
Start 689 ms
Risk FOUT — text flashes from fallback to web font
Marr-Sans-Bold.woff2 woff2 swap
Size 25 KB
Load time 26 ms
Start 690 ms
Risk FOUT — text flashes from fallback to web font
Darby-Rg.woff2 woff2 swap
Size 45 KB
Load time 25 ms
Start 690 ms
Risk FOUT — text flashes from fallback to web font
Marr-Sans-Rg.woff2 woff2 swap
Size 24 KB
Load time 23 ms
Start 691 ms
Risk FOUT — text flashes from fallback to web font
Marr-Sans-Ultra.woff2 woff2 swap
Size 24 KB
Load time 24 ms
Start 693 ms
Risk FOUT — text flashes from fallback to web font
fa-solid-900.54dfc8f5.w... woff2 swap
Size 135 KB
Load time 22 ms
Start 2.4 s
Risk FOUT — text flashes from fallback to web font
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
fa-light-300.d3271a56.w... woff2 swap
Size 181 KB
Load time 25 ms
Start 2.4 s
Risk FOUT — text flashes from fallback to web font
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
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 ~158 KB and ~316 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
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
Network Waterfall
44 requests over 2403ms
INFO
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s FCP 5.7 s LCP 13.0 shttps://cardiff.ac.uk// https://cardiff.ac.uk/ — 302 — 145 B — 27 ms — h2https://www.cardiff.ac.uk/www.cardiff.ac.uk/ https://www.cardiff.ac.uk/ — 200 — 28.0 KiB — 118 ms — h3https://d1pmxwirk3qc7v.cloudfront.net/dxp-includes/0b4962b9/dxp.cssd1pmxwirk3qc7v.cloudfront.net/dxp-i... https://d1pmxwirk3qc7v.cloudfront.net/dxp-includes/0b4962b9/dxp.css — 200 — 8.3 KiB — 311 ms — h3https://d3q5dbq2rziek.cloudfront.net/4.1.2/css/main.cssd3q5dbq2rziek.cloudfront.net/4.1.2/... https://d3q5dbq2rziek.cloudfront.net/4.1.2/css/main.css — 200 — 65.2 KiB — 300 ms — h2https://cardiff.imgix.net/__data/assets/image/0016/3040441/Screenshot-2026-04-16-130842.png?w=480&h=300&auto=format&fit=crop&q=20cardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0016/3040441/Screenshot-2026-04-16-130842.png?w=480&h=300&auto=format&fit=crop&q=20 — 200 — 5.9 KiB — 27 ms — h2https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/a3769b3f-a7ca-47bc-76ba-3276adba0f00/w=768,h=432,format=auto,fit=crop,q=60imagedelivery.net/RMCDRyHS-fPPUWNwh... https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/a3769b3f-a7ca-47bc-76ba-3276adba0f00/w=768,h=432,format=auto,fit=crop,q=60 — 200 — 20.9 KiB — 40 ms — h3https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/7ba709c7-7502-4a0d-6898-7df9adf03400/w=768,h=432,format=auto,fit=crop,q=60imagedelivery.net/RMCDRyHS-fPPUWNwh... https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/7ba709c7-7502-4a0d-6898-7df9adf03400/w=768,h=432,format=auto,fit=crop,q=60 — 200 — 40.7 KiB — 21 ms — h3https://cardiff.imgix.net/__data/assets/image/0005/2983181/getty-images-7mKwCbDgxRg-unsplash-2.jpg?w=570&h=321&fit=crop&q=60&auto=formatcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0005/2983181/getty-images-7mKwCbDgxRg-unsplash-2.jpg?w=570&h=321&fit=crop&q=60&auto=format — 200 — 9.0 KiB — 8 ms — h2https://cardiff.imgix.net/__data/assets/image/0006/2882301/Cardiff-Graduation-2024-181-1.jpg?w=570&h=321&fit=crop&q=60&auto=formatcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0006/2882301/Cardiff-Graduation-2024-181-1.jpg?w=570&h=321&fit=crop&q=60&auto=format — 200 — 19.9 KiB — 8 ms — h3https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/runtime.jsd3q5dbq2rziek.cloudfront.net/4.1.2/... https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/runtime.js — 200 — 2.1 KiB — 5 ms — h2https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/vendor.jsd3q5dbq2rziek.cloudfront.net/4.1.2/... https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/vendor.js — 200 — 50.9 KiB — 14 ms — h2https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/main.jsd3q5dbq2rziek.cloudfront.net/4.1.2/... https://d3q5dbq2rziek.cloudfront.net/4.1.2/js/main.js — 200 — 27.5 KiB — 21 ms — h2https://cardiff.imgix.net/__data/assets/image/0005/2971166/BRW-lead-header.jpg?auto=format&fit=crop&q=60&w=768&h=432cardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0005/2971166/BRW-lead-header.jpg?auto=format&fit=crop&q=60&w=768&h=432 — 200 — 23.9 KiB — 35 ms — h3https://cardiff.imgix.net/__data/assets/image/0006/2840370/CU_Research_2.jpg?w=600&h=343&q=90&auto=format&fit=cropcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0006/2840370/CU_Research_2.jpg?w=600&h=343&q=90&auto=format&fit=crop — 200 — 31.2 KiB — 40 ms — h3https://cardiff.imgix.net/__data/assets/image/0010/2853496/_CSP0105_crop.jpg?w=600&h=343&q=90&auto=format&fit=cropcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0010/2853496/_CSP0105_crop.jpg?w=600&h=343&q=90&auto=format&fit=crop — 200 — 18.0 KiB — 40 ms — h3https://cardiff.imgix.net/__data/assets/image/0007/2840398/169-crop-of-Grange-Pavilion-images-2-.png?w=600&h=343&q=90&auto=format&fit=cropcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0007/2840398/169-crop-of-Grange-Pavilion-images-2-.png?w=600&h=343&q=90&auto=format&fit=crop — 200 — 34.0 KiB — 40 ms — h3https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/4e6fd4c0-c303-48c7-65c7-fa5387784200/w=1920,h=1080,format=auto,fit=crop,q=60imagedelivery.net/RMCDRyHS-fPPUWNwh... https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/4e6fd4c0-c303-48c7-65c7-fa5387784200/w=1920,h=1080,format=auto,fit=crop,q=60 — 200 — 156.4 KiB — 40 ms — h3https://cardiff.imgix.net/__data/assets/image/0009/3040965/SIM-signing.JPG?w=570&h=321&fit=crop&q=60&auto=formatcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0009/3040965/SIM-signing.JPG?w=570&h=321&fit=crop&q=60&auto=format — 200 — 19.5 KiB — 39 ms — h3https://cardiff.imgix.net/__data/assets/image/0008/1279637/DefaultLogo.png?w=570&h=321&fit=crop&q=60&auto=formatcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0008/1279637/DefaultLogo.png?w=570&h=321&fit=crop&q=60&auto=format — 200 — 3.2 KiB — 40 ms — h3data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7data:image/gif;base64,R0lGODlhAQABA... data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7 — 200 — 0 B — 0 ms — datahttps://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/a3769b3f-a7ca-47bc-76ba-3276adba0f00/w=768,h=432,format=auto,fit=crop,q=60imagedelivery.net/RMCDRyHS-fPPUWNwh... https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/a3769b3f-a7ca-47bc-76ba-3276adba0f00/w=768,h=432,format=auto,fit=crop,q=60 — 200 — 344 B — 49 ms — h3https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/7ba709c7-7502-4a0d-6898-7df9adf03400/w=768,h=432,format=auto,fit=crop,q=60imagedelivery.net/RMCDRyHS-fPPUWNwh... 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h2https://cardiff.imgix.net/__data/assets/image/0005/2971166/BRW-lead-header.jpg?auto=format&fit=crop&q=60&w=768&h=432cardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0005/2971166/BRW-lead-header.jpg?auto=format&fit=crop&q=60&w=768&h=432 — 200 — 23.9 KiB — 35 ms — h3https://cardiff.imgix.net/__data/assets/image/0006/2840370/CU_Research_2.jpg?w=600&h=343&q=90&auto=format&fit=cropcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0006/2840370/CU_Research_2.jpg?w=600&h=343&q=90&auto=format&fit=crop — 200 — 31.2 KiB — 40 ms — h3https://cardiff.imgix.net/__data/assets/image/0010/2853496/_CSP0105_crop.jpg?w=600&h=343&q=90&auto=format&fit=cropcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0010/2853496/_CSP0105_crop.jpg?w=600&h=343&q=90&auto=format&fit=crop — 200 — 18.0 KiB — 40 ms — h3https://cardiff.imgix.net/__data/assets/image/0007/2840398/169-crop-of-Grange-Pavilion-images-2-.png?w=600&h=343&q=90&auto=format&fit=cropcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0007/2840398/169-crop-of-Grange-Pavilion-images-2-.png?w=600&h=343&q=90&auto=format&fit=crop — 200 — 34.0 KiB — 40 ms — h3https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/4e6fd4c0-c303-48c7-65c7-fa5387784200/w=1920,h=1080,format=auto,fit=crop,q=60imagedelivery.net/RMCDRyHS-fPPUWNwh... https://imagedelivery.net/RMCDRyHS-fPPUWNwhDDYEw/4e6fd4c0-c303-48c7-65c7-fa5387784200/w=1920,h=1080,format=auto,fit=crop,q=60 — 200 — 156.4 KiB — 40 ms — h3https://cardiff.imgix.net/__data/assets/image/0009/3040965/SIM-signing.JPG?w=570&h=321&fit=crop&q=60&auto=formatcardiff.imgix.net/__data/assets/ima... https://cardiff.imgix.net/__data/assets/image/0009/3040965/SIM-signing.JPG?w=570&h=321&fit=crop&q=60&auto=format — 200 — 19.5 KiB — 39 ms — 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— h2https://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Ultra.woff2d3q5dbq2rziek.cloudfront.net/4.1.2/... https://d3q5dbq2rziek.cloudfront.net/4.1.2/webfonts/Marr-Sans-Ultra.woff2 — 200 — 23.7 KiB — 24 ms — h2https://www.googletagmanager.com/gtag/js?id=DC-14284772&cx=c&gtm=4e64k0www.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=DC-14284772&cx=c&gtm=4e64k0 — 200 — 129.4 KiB — 27 ms — h2https://widget.geckoengage.com/embedwidget.geckoengage.com/embed https://widget.geckoengage.com/embed — 302 — 463 B — 33 ms — http/1.1https://widget.geckoengage.com/embed/widget.geckoengage.com/embed/ https://widget.geckoengage.com/embed/ — 200 — 286.4 KiB — 16 ms — http/1.1https://widget.geckoengage.com/embed/main.csswidget.geckoengage.com/embed/main.c... https://widget.geckoengage.com/embed/main.css — 200 — 178.5 KiB — 11 ms — http/1.1https://gag1babax2.execute-api.us-east-1.amazonaws.com/widgets/edad75b3-ebe4-4ec1-a888-e519fc3f3d64gag1babax2.execute-api.us-east-1.am... https://gag1babax2.execute-api.us-east-1.amazonaws.com/widgets/edad75b3-ebe4-4ec1-a888-e519fc3f3d64 — 200 — 1.1 KiB — 350 ms — h2https://www.google.com/ccm/collect?rcb=2&frm=0&en=page_view&dl=https%3A%2F%2Fwww.cardiff.ac.uk%2F&scrsrc=www.googletagmanager.com&rnd=571853401.1776894627&dt=Cardiff%20University&auid=501297363.1776894627&navt=n&npa=1&gtm=45fe64k0v9190820845z871661400za20gzb71661400zd71661400xec&gcd=13l3l3l2l1l1&dma_cps=a&dma=1&tag_exp=0~115938466~115938469~117266401~117384405&apve=1&apvf=f&apvc=1&tids=DC-14284772&tid=DC-14284772&tft=1776894627338&tfd=1033www.google.com/ccm/collect?rcb=2&fr... 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180.5 KiB — 25 ms — http/1.1
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 3139ms · 445KB · £33/mo
Google Tag Manager
Tag Manager
Costly
Execution 753ms
Transfer 192 KB
Unused 41%
Monthly Cost £8/mo
www.cardiff.ac.uk
Other
Costly
Execution 742ms
Transfer 28 KB
Monthly Cost £8/mo
d3q5dbq2rziek.cloudfront.net
Other
Costly
Execution 554ms
Transfer 27 KB
Monthly Cost £6/mo
Unattributable
Other
Costly
Execution 415ms
Transfer 0 KB
Monthly Cost £4/mo
Google Tag Manager
Tag Manager
Costly
Execution 318ms
Transfer 129 KB
Unused 48%
Monthly Cost £3/mo
widget.geckoengage.com
Other
Costly
Execution 211ms
Transfer 0 KB
Monthly Cost £2/mo
d3q5dbq2rziek.cloudfront.net
Other
Optional
Execution 87ms
Transfer 2 KB
Monthly Cost £1/mo
d3q5dbq2rziek.cloudfront.net
Other
Optional
Execution 59ms
Transfer 65 KB
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • Google Tag Manager adds 753ms and costs ~£8/month
  • www.cardiff.ac.uk adds 742ms and costs ~£8/month
  • d3q5dbq2rziek.cloudfront.net adds 554ms and costs ~£6/month
  • Unattributable adds 415ms and costs ~£4/month
  • Google Tag Manager adds 318ms and costs ~£3/month
  • widget.geckoengage.com adds 211ms 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

Google Tag Manager takes 753ms 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.cardiff.ac.uk takes 742ms 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

d3q5dbq2rziek.cloudfront.net takes 554ms 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

Unattributable takes 415ms 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

Google Tag Manager takes 318ms 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

widget.geckoengage.com takes 211ms 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

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