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https://commonslibrary.parliament.uk

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
81
GRADE
B
FIX
2
REVIEW
5
PASS
8
INFO
2

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

Mobile Desktop
55
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.
77
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.

2.61 s

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

3.17 s

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

440 ms

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

0.804

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

2.61 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.

7.61 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
8 PASS 5 REVIEW 2 FIX
D
Page Weight Inventory
Action
34 resources · 1.6 MB · 221 KB savings available
FIX
34 resources · 1.6 MB · 221 KB savings available
Warning::
Page weight 573 KB over 1MB target
Got: 1.6 MB Expected: ≤ 1 MB
Info::
~221 KB of savings available
Warning::
9 third-party resources (47% of weight)
Info::
1 resources over 200KB
34 resources · 1.6 MiB · 9 third-party 572.9 KiB over 1MB target
Image 49% · 788.3 KiB
JavaScript 33% · 532.8 KiB
CSS 12% · 185.5 KiB
Font 4% · 70.4 KiB
Document 1% · 17.8 KiB
Other 0% · 2.1 KiB

~220.9 KiB of savings available

Remove unused JavaScript: 220.9 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
Page Weight Budget
Action
1.6 MB transferred, 34 requests
REVIEW
1.6 MB transferred, 34 requests
Info::
Page weighs 3.0 MB (1.6 MB transferred)
Warning::
JavaScript is 533 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 533 KB
Info::
34 HTTP requests
Info::
Estimated 0.33 g CO2 per page load
1.6 MB / 2.4 MB budget
1.6 MB transferred
34 requests
0.33 g CO2 per page load
Images 783.5 KiB 49%
JavaScript 532.8 KiB 33%
CSS 185.5 KiB 12%
Fonts 70.4 KiB 4%
HTML 17.8 KiB 1%
Other 5.2 KiB 0%
Other 1.0 KiB 0%
Other 606 B 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

B
Third-Party Impact
47% third-party, 0 ms blocking
REVIEW
47% third-party, 0 ms blocking
Info::
Third-party code accounts for 47% of page weight (743.0 KiB of 1.6 MiB)
Info::
Third-party blocking time is low (0 ms)
53%
47%
First-party Third-party
C
Image Optimization
Action
12 images, 0 KB saveable
REVIEW
12 images, 0 KB saveable
Warning::
https://commonslibrary.parliament.uk/content/theme... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://commonslibrary.parliament.uk/content/theme... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://commonslibrary.parliament.uk/content/theme... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
12 images 783 KB
0 oversized -0 KB
12 legacy format
3 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

C
JS Execution Cost
Action
1536ms total JS execution
REVIEW
1536ms total JS execution
Warning::
https://www.googletagmanager.com/gtag/js?id=G-14RS...: 267ms CPU time
Warning::
Unattributable: 261ms CPU time
Info::
https://www.googletagmanager.com/gtag/js?id=G-9684...: 245ms CPU time
Info::
https://commonslibrary.parliament.uk/cdn-cgi/chall...: 243ms CPU time
Info::
https://commonslibrary.parliament.uk/: 219ms CPU time
Warning::
Third-party scripts: 1074ms (70% of total)

Main Thread Breakdown

Script Evaluation 59% Other 17% Script Parsing & Compilation 10% Style & Layout 7% Parse HTML & CSS 3%
ScriptTotalScriptingParse/CompileParty
https://www.googletagmanager.com/gtag/js?id=G-14RSNY7L8B&cx=c&gtm=4e64k1267ms207ms59ms3rd
Unattributable261ms5ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=G-9684J19FT4&cx=c&gtm=4e64k1245ms198ms46ms3rd
https://commonslibrary.parliament.uk/cdn-cgi/challenge-platform/scripts/jsd/main.js243ms237ms3ms1st
https://commonslibrary.parliament.uk/219ms36ms3ms1st
https://www.googletagmanager.com/gtm.js?id=GTM-TKRJ92L210ms178ms30ms3rd
https://cookiemanager.parliament.uk/cookiemanager.bundle.js90ms70ms11ms3rd
C
JS Bundles
Action
10 scripts, 221 KB unused
REVIEW
10 scripts, 221 KB unused
Warning::
https://www.googletagmanager.com/gtag/js?id=G-9684...: 66 KB unused (42%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=G-14RS...: 63 KB unused (41%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-TKR...: 63 KB unused (45%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://cookiemanager.parliament.uk/cookiemanager....: 29 KB unused (58%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 221 KB
221 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtag/js?id=G-9684J19FT4&cx=c&gtm=4e64k1157 KB66 KB (42%)✓3rd
https://www.googletagmanager.com/gtag/js?id=G-14RSNY7L8B&cx=c&gtm=4e64k1154 KB63 KB (41%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-TKRJ92L140 KB63 KB (45%)✓3rd
https://cookiemanager.parliament.uk/cookiemanager.bundle.js49 KB29 KB (58%)✓3rd
https://commonslibrary.parliament.uk/content/plugins/svg-support/vendor/DOMPurify/DOMPurify.min.js?ver=2.5.89 KB—✓1st
https://commonslibrary.parliament.uk/content/plugins/duracelltomi-google-tag-manager/dist/js/gtm4wp-form-move-tracker.js?ver=1.22.11 KB—✓1st
https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/app.min.js?ver=1.1.06 KB—✓1st
https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/libraries/lazysizes.min.js?ver=4.0.24 KB—✓1st
https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/libraries/ls.print.min.js?ver=1.0.01 KB—✓1st
https://commonslibrary.parliament.uk/cdn-cgi/challenge-platform/h/b/scripts/jsd/0b8fb825cb67/main.js?12 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

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+
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
2 fonts (70 KB)
PASS
2 fonts (70 KB)
Info::
2 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

2

70 KB total

Render-blocking

0

of 2

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 1.0 s 2.0 s 3.0 s FCP 2.6 s LCP 3.2 sdata:font/woff2;base64,d09GMgABAAAAAI52ABEAAAACJ8gAAI1dAAEAAAAAjcAAAAC2AAABbQAAAAAAAAAAG/A+HHAGYACK…A+HHAGYACK… data:font/woff2;base64,d09GMgABAAAAAI52ABEAAAACJ8gAAI1dAAEAAAAAjcAAAAC2AAABbQAAAAAAAAAAG/A+HHAGYACK… — 35.6 KiB — 25 ms — font-display: swapdata:font/woff2;base64,d09GMgABAAAAAIsKABEAAAACLUAAAInxAAEAAAAAilQAAAC2AAABbQAAAAAAAAAAG4GNFhxwBmAA…woff2;base64,d09GMgABAA... data:font/woff2;base64,d09GMgABAAAAAIsKABEAAAACLUAAAInxAAEAAAAAilQAAAC2AAABbQAAAAAAAAAAG4GNFhxwBmAA… — 34.8 KiB — 28 ms — font-display: swap
A+HHAGYACK… woff2 swap
Size 36 KB
Load time 25 ms
Start 296 ms
Risk FOUT — text flashes from fallback to web font
woff2;base64,d09GMgABAA... woff2 swap
Size 35 KB
Load time 28 ms
Start 296 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
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
A+
Green Hosting
Whether the site is served from green-energy infrastructure
PASS

Green Hosting

This site is hosted on green energy infrastructure

Provider: Cloudflare

Network Waterfall
34 requests over 706ms
INFO
0 ms 1.0 s 2.0 s 3.0 s FCP 2.6 s LCP 3.2 shttps://commonslibrary.parliament.uk// https://commonslibrary.parliament.uk/ — 200 — 17.8 KiB — 86 ms — h2https://commonslibrary.parliament.uk/content/plugins/svg-support/css/svgs-attachment.css/content/plugins/svg-support/css/sv... https://commonslibrary.parliament.uk/content/plugins/svg-support/css/svgs-attachment.css — 200 — 180 B — 45 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/styles/styles.min.css?ver=1.4.14/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/styles/styles.min.css?ver=1.4.14 — 200 — 14.0 KiB — 48 ms — h2https://commonslibrary.parliament.uk/content/themes/house-of-commons-library/style.css?ver=2.1.1/content/themes/house-of-commons-li... https://commonslibrary.parliament.uk/content/themes/house-of-commons-library/style.css?ver=2.1.1 — 200 — 569 B — 45 ms — h2https://commonslibrary.parliament.uk/content/plugins/svg-support/vendor/DOMPurify/DOMPurify.min.js?ver=2.5.8/content/plugins/svg-support/vendor... https://commonslibrary.parliament.uk/content/plugins/svg-support/vendor/DOMPurify/DOMPurify.min.js?ver=2.5.8 — 200 — 8.9 KiB — 46 ms — h2https://cookiemanager.parliament.uk/cookiemanager.csscookiemanager.parliament.uk/cookiem... https://cookiemanager.parliament.uk/cookiemanager.css — 200 — 170.8 KiB — 170 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-commons.svg/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-commons.svg — 200 — 4.2 KiB — 58 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-lords.svg?v=1/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-lords.svg?v=1 — 200 — 4.1 KiB — 56 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-post.svg/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-post.svg — 200 — 3.5 KiB — 57 ms — h3https://commonslibrary.parliament.uk/content/plugins/duracelltomi-google-tag-manager/dist/js/gtm4wp-form-move-tracker.js?ver=1.22.1/content/plugins/duracelltomi-googl... https://commonslibrary.parliament.uk/content/plugins/duracelltomi-google-tag-manager/dist/js/gtm4wp-form-move-tracker.js?ver=1.22.1 — 200 — 696 B — 43 ms — h3https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/app.min.js?ver=1.1.0/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/app.min.js?ver=1.1.0 — 200 — 5.6 KiB — 41 ms — h3https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/libraries/lazysizes.min.js?ver=4.0.2/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/libraries/lazysizes.min.js?ver=4.0.2 — 200 — 3.8 KiB — 45 ms — h3https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/libraries/ls.print.min.js?ver=1.0.0/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/js/libraries/ls.print.min.js?ver=1.0.0 — 200 — 836 B — 44 ms — h3https://cookiemanager.parliament.uk/cookiemanager.bundle.jscookiemanager.parliament.uk/cookiem... https://cookiemanager.parliament.uk/cookiemanager.bundle.js — 200 — 49.5 KiB — 81 ms — h2https://www.googletagmanager.com/gtm.js?id=GTM-TKRJ92Lwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-TKRJ92L — 200 — 140.2 KiB — 171 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/icon-breadcrumb.svg/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/icon-breadcrumb.svg — 200 — 651 B — 34 ms — h3https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/icon-chevron.svg/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/icon-chevron.svg — 200 — 709 B — 35 ms — h3data:font/woff2;base64,d09GMgABAAAAAI52ABEAAAACJ8gAAI1dAAEAAAAAjcAAAAC2AAABbQAAAAAAAAAAG/A+HHAGYACK…data:font/woff2;base64,d09GMgABAAAA... data:font/woff2;base64,d09GMgABAAAAAI52ABEAAAACJ8gAAI1dAAEAAAAAjcAAAAC2AAABbQAAAAAAAAAAG/A+HHAGYACK… — 200 — 35.6 KiB — 25 ms — datadata:font/woff2;base64,d09GMgABAAAAAIsKABEAAAACLUAAAInxAAEAAAAAilQAAAC2AAABbQAAAAAAAAAAG4GNFhxwBmAA…data:font/woff2;base64,d09GMgABAAAA... data:font/woff2;base64,d09GMgABAAAAAIsKABEAAAACLUAAAInxAAEAAAAAilQAAAC2AAABbQAAAAAAAAAAG4GNFhxwBmAA… — 200 — 34.8 KiB — 28 ms — datahttps://commonslibrary.parliament.uk/content/uploads/2023/03/portcullis-commons-green-background.jpg/content/uploads/2023/03/portcullis... https://commonslibrary.parliament.uk/content/uploads/2023/03/portcullis-commons-green-background.jpg — 200 — 11.0 KiB — 101 ms — h3https://commonslibrary.parliament.uk/content/uploads/2020/09/health-services-scaled-e1688999387321-1232x693.jpg/content/uploads/2020/09/health-ser... https://commonslibrary.parliament.uk/content/uploads/2020/09/health-services-scaled-e1688999387321-1232x693.jpg — 200 — 87.4 KiB — 140 ms — h3https://commonslibrary.parliament.uk/content/uploads/2025/07/Crowd-of-people-walking-busy-city-street-1232x693.jpeg/content/uploads/2025/07/Crowd-of-p... https://commonslibrary.parliament.uk/content/uploads/2025/07/Crowd-of-people-walking-busy-city-street-1232x693.jpeg — 200 — 114.4 KiB — 141 ms — h3https://commonslibrary.parliament.uk/content/uploads/2020/08/economic-situation-1232x924.jpg/content/uploads/2020/08/economic-s... https://commonslibrary.parliament.uk/content/uploads/2020/08/economic-situation-1232x924.jpg — 200 — 73.7 KiB — 137 ms — h3https://commonslibrary.parliament.uk/content/uploads/2026/04/Geograph-6099508-Robert-Lamb-1232x693.jpg/content/uploads/2026/04/Geograph-6... https://commonslibrary.parliament.uk/content/uploads/2026/04/Geograph-6099508-Robert-Lamb-1232x693.jpg — 200 — 138.7 KiB — 157 ms — h3https://commonslibrary.parliament.uk/content/uploads/2025/01/Iran-flag-Tehran-skyline-AS-1232x693.jpeg/content/uploads/2025/01/Iran-flag-... https://commonslibrary.parliament.uk/content/uploads/2025/01/Iran-flag-Tehran-skyline-AS-1232x693.jpeg — 200 — 89.7 KiB — 140 ms — h3https://commonslibrary.parliament.uk/cdn-cgi/challenge-platform/scripts/jsd/main.js/cdn-cgi/challenge-platform/scripts... https://commonslibrary.parliament.uk/cdn-cgi/challenge-platform/scripts/jsd/main.js — 302 — 450 B — 39 ms — h3https://commonslibrary.parliament.uk/content/uploads/2025/07/georg-eiermann-mW7H9WGw9HQ-unsplash-1232x693.jpg/content/uploads/2025/07/georg-eier... https://commonslibrary.parliament.uk/content/uploads/2025/07/georg-eiermann-mW7H9WGw9HQ-unsplash-1232x693.jpg — 200 — 255.5 KiB — 134 ms — h3https://commonslibrary.parliament.uk/cdn-cgi/challenge-platform/h/b/scripts/jsd/0b8fb825cb67/main.js?/cdn-cgi/challenge-platform/h/b/scr... https://commonslibrary.parliament.uk/cdn-cgi/challenge-platform/h/b/scripts/jsd/0b8fb825cb67/main.js? — 200 — 11.8 KiB — 91 ms — h3https://www.googletagmanager.com/gtag/js?id=G-14RSNY7L8B&cx=c&gtm=4e64k1www.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-14RSNY7L8B&cx=c&gtm=4e64k1 — 200 — 154.2 KiB — 64 ms — h2https://www.googletagmanager.com/gtag/js?id=G-9684J19FT4&cx=c&gtm=4e64k1www.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-9684J19FT4&cx=c&gtm=4e64k1 — 200 — 157.4 KiB — 85 ms — h2
0 ms 1.0 s 2.0 s 3.0 s FCP 2.6 s LCP 3.2 shttps://commonslibrary.parliament.uk// https://commonslibrary.parliament.uk/ — 200 — 17.8 KiB — 86 ms — h2https://commonslibrary.parliament.uk/content/plugins/svg-support/css/svgs-attachment.css/content/plugins/svg-support/css/sv... https://commonslibrary.parliament.uk/content/plugins/svg-support/css/svgs-attachment.css — 200 — 180 B — 45 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/styles/styles.min.css?ver=1.4.14/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/styles/styles.min.css?ver=1.4.14 — 200 — 14.0 KiB — 48 ms — h2https://commonslibrary.parliament.uk/content/themes/house-of-commons-library/style.css?ver=2.1.1/content/themes/house-of-commons-li... https://commonslibrary.parliament.uk/content/themes/house-of-commons-library/style.css?ver=2.1.1 — 200 — 569 B — 45 ms — h2https://commonslibrary.parliament.uk/content/plugins/svg-support/vendor/DOMPurify/DOMPurify.min.js?ver=2.5.8/content/plugins/svg-support/vendor... https://commonslibrary.parliament.uk/content/plugins/svg-support/vendor/DOMPurify/DOMPurify.min.js?ver=2.5.8 — 200 — 8.9 KiB — 46 ms — h2https://cookiemanager.parliament.uk/cookiemanager.csscookiemanager.parliament.uk/cookiem... https://cookiemanager.parliament.uk/cookiemanager.css — 200 — 170.8 KiB — 170 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-commons.svg/content/themes/parliament-design-s... https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-commons.svg — 200 — 4.2 KiB — 58 ms — h2https://commonslibrary.parliament.uk/content/themes/parliament-design-system/dist/assets/svg/logo_ukp-lords.svg?v=1/content/themes/parliament-design-s... 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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
70% of JavaScript execution is third-party
First-party Third-party 1074ms · 501KB · £11/mo
Google Tag Manager
Tag Manager
Costly
Execution 267ms
Transfer 154 KB
Unused 41%
Monthly Cost £3/mo
Unattributable
Other
Costly
Execution 261ms
Transfer 0 KB
Monthly Cost £3/mo
Google Tag Manager
Tag Manager
Costly
Execution 245ms
Transfer 157 KB
Unused 42%
Monthly Cost £3/mo
Google Tag Manager
Tag Manager
Costly
Execution 210ms
Transfer 140 KB
Unused 45%
Monthly Cost £2/mo
cookiemanager.parliament.uk
Other
Optional
Execution 90ms
Transfer 49 KB
Unused 58%
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • Google Tag Manager adds 267ms and costs ~£3/month
  • Unattributable adds 261ms and costs ~£3/month
  • Google Tag Manager adds 245ms and costs ~£3/month
  • Google Tag Manager adds 210ms and costs ~£2/month

70% 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

Google Tag Manager takes 267ms 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 261ms 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 245ms 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 210ms 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

58% of cookiemanager.parliament.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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