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Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
74
GRADE
C
FIX
5
REVIEW
3
PASS
7
INFO
2

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

Mobile Desktop
34
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
97
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.
83
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.

7.43 s

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

15.68 s

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

1.08 s

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

0.055

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

7.84 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.

15.78 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
7 PASS 3 REVIEW 5 FIX
F
Page Weight Budget
Action
5.1 MB transferred, 67 requests
FIX
5.1 MB transferred, 67 requests
Critical::
Page weighs 9.1 MB (5.1 MB transferred)
Warning::
Images are 3.7 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 3.7 MB
Warning::
JavaScript is 1.1 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.1 MB
Info::
67 HTTP requests
Info::
Estimated 1.1 g CO2 per page load
5.1 MB / 2.4 MB budget
5.1 MB transferred
67 requests
1.1 g CO2 per page load
Images 3.7 MiB 72%
JavaScript 1.1 MiB 22%
CSS 133.2 KiB 3%
Fonts 79.6 KiB 2%
HTML 62.0 KiB 1%
Other 39.6 KiB 1%
Other 3.3 KiB 0%
Other 1.5 KiB 0%
Other 0 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

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

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 (5.1 MiB of 5.1 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Execution Cost
Action
3080ms total JS execution
FIX
3080ms total JS execution
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-KTX...: 1046ms CPU time
Warning::
Unattributable: 1017ms CPU time
Warning::
https://cdn.cookielaw.org/scripttemplates/202311.1...: 503ms CPU time
Warning::
https://www.tcd.ie/: 315ms CPU time
Info::
https://www.tcd.ie/media/tcd/site-assets/scripts/j...: 129ms CPU time
Warning::
Third-party scripts: 3080ms (100% of total)

Main Thread Breakdown

Script Evaluation 50% Other 28% Script Parsing & Compilation 9% Style & Layout 8% Parse HTML & CSS 4%
ScriptTotalScriptingParse/CompileParty
https://www.googletagmanager.com/gtm.js?id=GTM-KTX8CV1046ms849ms141ms3rd
Unattributable1017ms185ms0ms3rd
https://cdn.cookielaw.org/scripttemplates/202311.1.0/otBannerSdk.js503ms320ms80ms3rd
https://www.tcd.ie/315ms21ms4ms3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/jquery-3.5.1.min.js129ms99ms17ms3rd
https://cdn.cookielaw.org/scripttemplates/otSDKStub.js70ms52ms5ms3rd
D
Page Weight Inventory
Action
67 resources · 5.1 MB · 119 KB savings available
FIX
67 resources · 5.1 MB · 119 KB savings available
Warning::
Page weight 4.1 MB over 1MB target
Got: 5.1 MB Expected: ≤ 1 MB
Info::
~119 KB of savings available
Warning::
66 third-party resources (100% of weight)
Info::
2 resources over 200KB
67 resources · 5.1 MiB · 66 third-party 4.1 MiB over 1MB target
Image 72% · 3.7 MiB
JavaScript 22% · 1.1 MiB
CSS 3% · 137.1 KiB
Font 2% · 79.6 KiB
Document 1% · 62.1 KiB
Other 1% · 37.7 KiB

~118.9 KiB of savings available

Remove unused JavaScript: 118.9 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
Image Optimization
Action
24 images, 0 KB saveable
REVIEW
24 images, 0 KB saveable
Warning::
https://www.tcd.ie/media/tcd/site-assets/images/tc... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://pxl-tcdie.terminalfour.net/fit-in/200x50/f... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://pxl-tcdie.terminalfour.net/fit-in/200x50/f... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://pxl-tcdie.terminalfour.net/fit-in/200x50/f... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
24 images 3.7 MB
0 oversized -0 KB
15 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 Bundles
17 scripts, 119 KB unused
REVIEW
17 scripts, 119 KB unused
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-KTX...: 65 KB unused (34%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://cdn.cookielaw.org/scripttemplates/202311.1...: 54 KB unused (52%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.tcd.ie/media/tcd/site-assets/scripts/g...: unminified — 3 KB could be saved
Info::
Total unused JavaScript: 119 KB
119 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtm.js?id=GTM-KTX8CV190 KB65 KB (34%)✓3rd
https://cdn.cookielaw.org/scripttemplates/202311.1.0/otBannerSdk.js103 KB54 KB (52%)✓3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/global-20220428.js7 KB—✗3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/jquery-3.5.1.min.js31 KB—✓3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/van11y-accessible-tab-panel-aria.min.js3 KB—✓3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/emergency.js2 KB—✓3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/emergency-micro.js2 KB—✓3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/t4-updates.js1 KB—✓3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/ofi.min.js2 KB—✓3rd
https://www.tcd.ie/media/tcd/site-assets/scripts/tiny-slider.min.js13 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

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+
Font Loading
4 fonts (80 KB)
PASS
4 fonts (80 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

80 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 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s 16.0 s FCP 7.4 s LCP 15.7 shttps://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 33.9 KiB — 30 ms — font-display: swaphttps://www.tcd.ie/media/tcd/site-assets/fonts/open-sans-latin-regular.woff2open-sans-latin-regular... https://www.tcd.ie/media/tcd/site-assets/fonts/open-sans-latin-regular.woff2 — 14.4 KiB — 155 ms — font-display: swaphttps://www.tcd.ie/media/tcd/site-assets/fonts/source-sans-pro-latin-regular.woff2source-sans-pro-latin-r... https://www.tcd.ie/media/tcd/site-assets/fonts/source-sans-pro-latin-regular.woff2 — 16.1 KiB — 174 ms — font-display: swaphttps://www.tcd.ie/media/tcd/site-assets/fonts/open-sans-latin-700.woff2open-sans-latin-700.woff2 https://www.tcd.ie/media/tcd/site-assets/fonts/open-sans-latin-700.woff2 — 15.1 KiB — 172 ms — font-display: swap
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 34 KB
Load time 30 ms
Start 713 ms
Risk FOUT — text flashes from fallback to web font
open-sans-latin-regular... woff2 swap
Size 14 KB
Load time 155 ms
Start 1.0 s
Risk FOUT — text flashes from fallback to web font
source-sans-pro-latin-r... woff2 swap
Size 16 KB
Load time 174 ms
Start 1.0 s
Risk FOUT — text flashes from fallback to web font
open-sans-latin-700.woff2 woff2 swap
Size 15 KB
Load time 172 ms
Start 1.4 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+
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
67 requests over 6025ms
INFO
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s 16.0 s FCP 7.4 s LCP 15.7 shttps://tcd.ie// https://tcd.ie/ — 301 — 81 B — 61 ms — h2https://www.tcd.ie/www.tcd.ie/ https://www.tcd.ie/ — 200 — 5.7 KiB — 298 ms — h2https://www.tcd.ie/media/tcd/site-assets/style/20220428-tcd-style.csswww.tcd.ie/media/tcd/site-assets/st... https://www.tcd.ie/media/tcd/site-assets/style/20220428-tcd-style.css — 200 — 29.7 KiB — 186 ms — h2https://cdnjs.cloudflare.com/ajax/libs/tiny-slider/2.9.2/tiny-slider.csscdnjs.cloudflare.com/ajax/libs/tiny... https://cdnjs.cloudflare.com/ajax/libs/tiny-slider/2.9.2/tiny-slider.css — 200 — 1.2 KiB — 21 ms — h3https://www.tcd.ie/media/tcd/site-assets/images/tcd-logo.pngwww.tcd.ie/media/tcd/site-assets/im... https://www.tcd.ie/media/tcd/site-assets/images/tcd-logo.png — 200 — 10.6 KiB — 217 ms — h2https://pxl-tcdie.terminalfour.net/fit-in/480x9999/filters:no_upscale()/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/homepage/images/frontsquare-2025-smalljpg.jpgpxl-tcdie.terminalfour.net/fit-in/4... https://pxl-tcdie.terminalfour.net/fit-in/480x9999/filters:no_upscale()/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/homepage/images/frontsquare-2025-smalljpg.jpg — 200 — 90.6 KiB — 582 ms — h2https://pxl-tcdie.terminalfour.net/prod01/channel_3/media/tcd/homepage/image-f-(2).jpgpxl-tcdie.terminalfour.net/prod01/c... https://pxl-tcdie.terminalfour.net/prod01/channel_3/media/tcd/homepage/image-f-(2).jpg — 200 — 43.3 KiB — 385 ms — h2https://www.trumba.com/i/DgBvYPNi1ryfntQXbnEewTJW.jpgwww.trumba.com/i/DgBvYPNi1ryfntQXbn... https://www.trumba.com/i/DgBvYPNi1ryfntQXbnEewTJW.jpg — 200 — 141.8 KiB — 911 ms — http/1.1https://www.trumba.com/i/DgAwEE7nAIqYokAtzwbaF6Vt.jpgwww.trumba.com/i/DgAwEE7nAIqYokAtzw... https://www.trumba.com/i/DgAwEE7nAIqYokAtzwbaF6Vt.jpg — 200 — 36.8 KiB — 616 ms — http/1.1https://www.tcd.ie/media/tcd/site-assets/scripts/ofi.min.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/ofi.min.js — 200 — 1.8 KiB — 203 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/focus-visible.min.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/focus-visible.min.js — 200 — 1.4 KiB — 187 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/jquery-3.5.1.min.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/jquery-3.5.1.min.js — 200 — 30.6 KiB — 233 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/tiny-slider.min.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/tiny-slider.min.js — 200 — 12.9 KiB — 221 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/van11y-accessible-tab-panel-aria.min.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/van11y-accessible-tab-panel-aria.min.js — 200 — 2.5 KiB — 207 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/emergency.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/emergency.js — 200 — 2.4 KiB — 241 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/emergency-micro.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/emergency-micro.js — 200 — 2.3 KiB — 249 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/t4-updates.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/t4-updates.js — 200 — 790 B — 224 ms — h2https://www.tcd.ie/media/tcd/site-assets/scripts/global-20220428.jswww.tcd.ie/media/tcd/site-assets/sc... https://www.tcd.ie/media/tcd/site-assets/scripts/global-20220428.js — 200 — 7.4 KiB — 243 ms — h2https://www.trumba.com/i/DgALofSC2uXdgIYr-0%2ACwWat.pngwww.trumba.com/i/DgALofSC2uXdgIYr-0... https://www.trumba.com/i/DgALofSC2uXdgIYr-0%2ACwWat.png — 200 — 2.9 MiB — 5.2 s — http/1.1https://www.tcd.ie/media/tcd/site-assets/images/facebook.svgwww.tcd.ie/media/tcd/site-assets/im... https://www.tcd.ie/media/tcd/site-assets/images/facebook.svg — 200 — 694 B — 179 ms — h2https://www.tcd.ie/media/tcd/site-assets/images/Instagram.svgwww.tcd.ie/media/tcd/site-assets/im... https://www.tcd.ie/media/tcd/site-assets/images/Instagram.svg — 200 — 1.3 KiB — 252 ms — h2https://www.tcd.ie/media/tcd/site-assets/images/x-logo.svgwww.tcd.ie/media/tcd/site-assets/im... https://www.tcd.ie/media/tcd/site-assets/images/x-logo.svg — 200 — 829 B — 249 ms — h2https://www.tcd.ie/media/tcd/site-assets/images/youtube.svgwww.tcd.ie/media/tcd/site-assets/im... https://www.tcd.ie/media/tcd/site-assets/images/youtube.svg — 200 — 1.1 KiB — 219 ms — h2https://www.tcd.ie/media/tcd/site-assets/images/linkedin.svgwww.tcd.ie/media/tcd/site-assets/im... https://www.tcd.ie/media/tcd/site-assets/images/linkedin.svg — 200 — 701 B — 233 ms — h2https://pxl-tcdie.terminalfour.net/fit-in/200x50/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/athenaswan.pngpxl-tcdie.terminalfour.net/fit-in/2... https://pxl-tcdie.terminalfour.net/fit-in/200x50/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/athenaswan.png — 200 — 2.8 KiB — 367 ms — h2https://pxl-tcdie.terminalfour.net/fit-in/200x50/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/content-assets/images/coimbragroupuniversities.pngpxl-tcdie.terminalfour.net/fit-in/2... https://pxl-tcdie.terminalfour.net/fit-in/200x50/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/content-assets/images/coimbragroupuniversities.png — 200 — 2.2 KiB — 369 ms — h2https://pxl-tcdie.terminalfour.net/fit-in/200x50/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/content-assets/images/leru.pngpxl-tcdie.terminalfour.net/fit-in/2... https://pxl-tcdie.terminalfour.net/fit-in/200x50/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/content-assets/images/leru.png — 200 — 1.9 KiB — 373 ms — h2https://www.googletagmanager.com/gtm.js?id=GTM-KTX8CVwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-KTX8CV — 200 — 190.3 KiB — 47 ms — h2https://www.youtube.com/embed/V1ggffYdjzUwww.youtube.com/embed/V1ggffYdjzU https://www.youtube.com/embed/V1ggffYdjzU — 200 — 56.3 KiB — 80 ms — h2https://www.youtube.com/s/player/218d9d92/www-player.csswww.youtube.com/s/player/218d9d92/w... https://www.youtube.com/s/player/218d9d92/www-player.css — 200 — 56.9 KiB — 43 ms — h2
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s 16.0 s FCP 7.4 s LCP 15.7 shttps://tcd.ie// https://tcd.ie/ — 301 — 81 B — 61 ms — h2https://www.tcd.ie/www.tcd.ie/ https://www.tcd.ie/ — 200 — 5.7 KiB — 298 ms — h2https://www.tcd.ie/media/tcd/site-assets/style/20220428-tcd-style.csswww.tcd.ie/media/tcd/site-assets/st... https://www.tcd.ie/media/tcd/site-assets/style/20220428-tcd-style.css — 200 — 29.7 KiB — 186 ms — h2https://cdnjs.cloudflare.com/ajax/libs/tiny-slider/2.9.2/tiny-slider.csscdnjs.cloudflare.com/ajax/libs/tiny... https://cdnjs.cloudflare.com/ajax/libs/tiny-slider/2.9.2/tiny-slider.css — 200 — 1.2 KiB — 21 ms — h3https://www.tcd.ie/media/tcd/site-assets/images/tcd-logo.pngwww.tcd.ie/media/tcd/site-assets/im... https://www.tcd.ie/media/tcd/site-assets/images/tcd-logo.png — 200 — 10.6 KiB — 217 ms — h2https://pxl-tcdie.terminalfour.net/fit-in/480x9999/filters:no_upscale()/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/homepage/images/frontsquare-2025-smalljpg.jpgpxl-tcdie.terminalfour.net/fit-in/4... https://pxl-tcdie.terminalfour.net/fit-in/480x9999/filters:no_upscale()/filters:format(webp)/filters:quality(100)/prod01/channel_3/media/tcd/homepage/images/frontsquare-2025-smalljpg.jpg — 200 — 90.6 KiB — 582 ms — h2https://pxl-tcdie.terminalfour.net/prod01/channel_3/media/tcd/homepage/image-f-(2).jpgpxl-tcdie.terminalfour.net/prod01/c... https://pxl-tcdie.terminalfour.net/prod01/channel_3/media/tcd/homepage/image-f-(2).jpg — 200 — 43.3 KiB — 385 ms — h2https://www.trumba.com/i/DgBvYPNi1ryfntQXbnEewTJW.jpgwww.trumba.com/i/DgBvYPNi1ryfntQXbn... https://www.trumba.com/i/DgBvYPNi1ryfntQXbnEewTJW.jpg — 200 — 141.8 KiB — 911 ms — http/1.1https://www.trumba.com/i/DgAwEE7nAIqYokAtzwbaF6Vt.jpgwww.trumba.com/i/DgAwEE7nAIqYokAtzw... 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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 3080ms · 339KB · €33/mo
Google Tag Manager
Tag Manager
Costly
Execution 1046ms
Transfer 190 KB
Unused 34%
Monthly Cost €11/mo
Unattributable
Other
Costly
Execution 1017ms
Transfer 0 KB
Monthly Cost €11/mo
OneTrust
Consent
Essential
Execution 503ms
Transfer 103 KB
Unused 52%
Monthly Cost €5/mo
www.tcd.ie
Other
Costly
Execution 315ms
Transfer 6 KB
Monthly Cost €3/mo
www.tcd.ie
Other
Optional
Execution 129ms
Transfer 31 KB
Monthly Cost €1/mo
OneTrust
Consent
Essential
Execution 70ms
Transfer 9 KB
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • Google Tag Manager adds 1046ms and costs ~€11/month
  • Unattributable adds 1017ms and costs ~€11/month
  • www.tcd.ie adds 315ms and costs ~€3/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 1046ms 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 1017ms 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

52% of OneTrust'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

www.tcd.ie takes 315ms 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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