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Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
79
GRADE
C
FIX
4
REVIEW
2
PASS
7
INFO
2

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

Mobile Desktop
89
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
96
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.

1.01 s

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

1.92 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.

0.043

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

1.23 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.

2.16 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 2 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 (1.4 MiB of 1.4 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Bundles
Action
5 scripts, 348 KB unused
FIX
5 scripts, 348 KB unused
Warning::
https://www.aboutcookies.org/assets/js/index.js?v=...: 224 KB unused (75%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=G-463C...: 63 KB unused (44%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-WQZ...: 61 KB unused (46%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 348 KB
348 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.aboutcookies.org/assets/js/index.js?v=20260418003154299 KB224 KB (75%)✓3rd
https://www.googletagmanager.com/gtag/js?id=G-463CHWS42G&cx=c&gtm=4e64h1144 KB63 KB (44%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-WQZFSCP133 KB61 KB (46%)✓3rd
https://az416426.vo.msecnd.net/scripts/a/ai.0.js22 KB—✓3rd
https://www.google-analytics.com/analytics.js21 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

D
Page Weight Inventory
Action
26 resources · 1.4 MB · 348 KB savings available
FIX
26 resources · 1.4 MB · 348 KB savings available
Warning::
Page weight 436 KB over 1MB target
Got: 1.4 MB Expected: ≤ 1 MB
Info::
~348 KB of savings available
Warning::
25 third-party resources (100% of weight)
Info::
2 resources over 200KB
26 resources · 1.4 MiB · 25 third-party 435.5 KiB over 1MB target
JavaScript 42% · 618.8 KiB
Image 35% · 507.7 KiB
CSS 10% · 152.4 KiB
Font 10% · 146.1 KiB
Document 2% · 32.1 KiB
Other 0% · 2.3 KiB

~348.4 KiB of savings available

Remove unused JavaScript: 348.4 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.

B
Page Weight Budget
1.4 MB transferred, 26 requests
REVIEW
1.4 MB transferred, 26 requests
Info::
Page weighs 4.0 MB (1.4 MB transferred)
Warning::
JavaScript is 619 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 619 KB
Info::
26 HTTP requests
Info::
Estimated 0.30 g CO2 per page load
1.4 MB / 2.4 MB budget
1.4 MB transferred
26 requests
0.30 g CO2 per page load
JavaScript 618.8 KiB 42%
Images 504.5 KiB 35%
CSS 152.4 KiB 10%
Fonts 146.1 KiB 10%
HTML 32.1 KiB 2%
Other 3.7 KiB 0%
Other 1.0 KiB 0%
Other 552 B 0%
Other 327 B 0%
Other 0 B 0%
0 2.4 MB 4.9 MB
Under budget

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

C
Image Optimization
Action
7 images, 0 KB saveable
REVIEW
7 images, 0 KB saveable
Warning::
https://www.aboutcookies.org/-/media/images/campai... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.aboutcookies.org/-/media/images/campai... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.aboutcookies.org/-/media/images/campai... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.aboutcookies.org/-/media/images/campai... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
7 images 504 KB
0 oversized -0 KB
6 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

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
338ms total JS execution
PASS
338ms total JS execution
Info::
https://www.aboutcookies.org/: 136ms CPU time
Info::
https://www.aboutcookies.org/assets/js/index.js?v=...: 84ms CPU time
Info::
Unattributable: 67ms CPU time
Info::
https://www.googletagmanager.com/gtag/js?id=G-463C...: 52ms CPU time
Warning::
Third-party scripts: 338ms (100% of total)

Main Thread Breakdown

Script Evaluation 37% Other 34% Script Parsing & Compilation 12% Style & Layout 9% Parse HTML & CSS 6%
ScriptTotalScriptingParse/CompileParty
https://www.aboutcookies.org/136ms13ms1ms3rd
https://www.aboutcookies.org/assets/js/index.js?v=2026041800315484ms39ms25ms3rd
Unattributable67ms2ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=G-463CHWS42G&cx=c&gtm=4e64h152ms41ms11ms3rd
A+
Font Loading
4 fonts (146 KB)
PASS
4 fonts (146 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

146 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 1.0 s LCP 1.9 shttps://www.aboutcookies.org/assets/fonts/BlsW-Bd/blsw-bd.woff2blsw-bd.woff2 https://www.aboutcookies.org/assets/fonts/BlsW-Bd/blsw-bd.woff2 — 36.5 KiB — 95 ms — font-display: swaphttps://www.aboutcookies.org/assets/fonts/BlsW-Md/blsw-md.woff2blsw-md.woff2 https://www.aboutcookies.org/assets/fonts/BlsW-Md/blsw-md.woff2 — 36.4 KiB — 89 ms — font-display: swaphttps://www.aboutcookies.org/assets/fonts/BlsW-Rg/blsw-rg.woff2blsw-rg.woff2 https://www.aboutcookies.org/assets/fonts/BlsW-Rg/blsw-rg.woff2 — 36.7 KiB — 99 ms — font-display: swaphttps://www.aboutcookies.org/assets/fonts/BlsW-Lt/blsw-lt.woff2blsw-lt.woff2 https://www.aboutcookies.org/assets/fonts/BlsW-Lt/blsw-lt.woff2 — 36.5 KiB — 92 ms — font-display: swap
blsw-bd.woff2 woff2 swap
Size 36 KB
Load time 95 ms
Start 218 ms
Risk FOUT — text flashes from fallback to web font
blsw-md.woff2 woff2 swap
Size 36 KB
Load time 89 ms
Start 218 ms
Risk FOUT — text flashes from fallback to web font
blsw-rg.woff2 woff2 swap
Size 37 KB
Load time 99 ms
Start 218 ms
Risk FOUT — text flashes from fallback to web font
blsw-lt.woff2 woff2 swap
Size 37 KB
Load time 92 ms
Start 219 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+
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
26 requests over 959ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s FCP 1.0 s LCP 1.9 shttps://aboutcookies.org// https://aboutcookies.org/ — 301 — 463 B — 48 ms — h3https://www.aboutcookies.org/www.aboutcookies.org/ https://www.aboutcookies.org/ — 200 — 32.1 KiB — 161 ms — h3https://www.aboutcookies.org/site.webmanifestwww.aboutcookies.org/site.webmanife... https://www.aboutcookies.org/site.webmanifest — 200 — 1.0 KiB — 71 ms — h3https://www.aboutcookies.org/assets/css/force-load.css?v=20260418003154www.aboutcookies.org/assets/css/for... https://www.aboutcookies.org/assets/css/force-load.css?v=20260418003154 — 200 — 8.7 KiB — 49 ms — h3https://www.aboutcookies.org/assets/css/main.css?v=20260418003154www.aboutcookies.org/assets/css/mai... https://www.aboutcookies.org/assets/css/main.css?v=20260418003154 — 200 — 120.9 KiB — 120 ms — h3https://www.aboutcookies.org/assets/fonts/BlsW-Bd/blsw-bd.woff2www.aboutcookies.org/assets/fonts/B... https://www.aboutcookies.org/assets/fonts/BlsW-Bd/blsw-bd.woff2 — 200 — 36.5 KiB — 95 ms — h3https://www.aboutcookies.org/assets/fonts/BlsW-Md/blsw-md.woff2www.aboutcookies.org/assets/fonts/B... https://www.aboutcookies.org/assets/fonts/BlsW-Md/blsw-md.woff2 — 200 — 36.4 KiB — 89 ms — h3https://www.aboutcookies.org/assets/fonts/BlsW-Rg/blsw-rg.woff2www.aboutcookies.org/assets/fonts/B... https://www.aboutcookies.org/assets/fonts/BlsW-Rg/blsw-rg.woff2 — 200 — 36.7 KiB — 99 ms — h3https://www.aboutcookies.org/assets/fonts/BlsW-Lt/blsw-lt.woff2www.aboutcookies.org/assets/fonts/B... https://www.aboutcookies.org/assets/fonts/BlsW-Lt/blsw-lt.woff2 — 200 — 36.5 KiB — 92 ms — h3data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==data:image/gif;base64,R0lGODlhAQABA... data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw== — 200 — 0 B — 0 ms — datahttps://www.googletagmanager.com/gtm.js?id=GTM-WQZFSCPwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-WQZFSCP — 200 — 132.8 KiB — 148 ms — h2https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_hhhero_1440x700px.png?h=700&w=1440&rev=65450da021d64333bc47e89afbdb3ad4&hash=734E24372BE3E9BB9EB19CEED202FC18www.aboutcookies.org/-/media/images... https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_hhhero_1440x700px.png?h=700&w=1440&rev=65450da021d64333bc47e89afbdb3ad4&hash=734E24372BE3E9BB9EB19CEED202FC18 — 200 — 232.9 KiB — 118 ms — h3https://www.aboutcookies.org/assets/css/icons/icons.data.svg.csswww.aboutcookies.org/assets/css/ico... https://www.aboutcookies.org/assets/css/icons/icons.data.svg.css — 200 — 22.7 KiB — 82 ms — h3https://az416426.vo.msecnd.net/scripts/a/ai.0.jsaz416426.vo.msecnd.net/scripts/a/ai... https://az416426.vo.msecnd.net/scripts/a/ai.0.js — 200 — 21.6 KiB — 146 ms — h2https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_standard_image_card_695x358_how_to_control_cookies.png?h=358&w=695&rev=09b594ef059b465eb33ff33cdcd9feef&hash=A2943ED676276D934C8BA63E65229186www.aboutcookies.org/-/media/images... https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_standard_image_card_695x358_how_to_control_cookies.png?h=358&w=695&rev=09b594ef059b465eb33ff33cdcd9feef&hash=A2943ED676276D934C8BA63E65229186 — 200 — 65.8 KiB — 104 ms — h3https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_standard_image_card_695x358_cookies_faq.png?h=358&w=695&rev=d80c39f912f3428bb4a80f86959e456e&hash=A119BBB35194D91BAB423CD8905C7B5Dwww.aboutcookies.org/-/media/images... https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_standard_image_card_695x358_cookies_faq.png?h=358&w=695&rev=d80c39f912f3428bb4a80f86959e456e&hash=A119BBB35194D91BAB423CD8905C7B5D — 200 — 70.8 KiB — 104 ms — h3https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_standard_image_card_695x358_cookie_law.png?h=358&w=695&rev=c2cf7c861d93442bae3c38dbab08aa72&hash=634F480EEBA17496B67387D845680D4Bwww.aboutcookies.org/-/media/images... https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_standard_image_card_695x358_cookie_law.png?h=358&w=695&rev=c2cf7c861d93442bae3c38dbab08aa72&hash=634F480EEBA17496B67387D845680D4B — 200 — 69.5 KiB — 109 ms — h3https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_standard_image_card_695x358_eu.png?h=358&w=695&rev=84a63244506d49a4866552cadcf3f896&hash=D0039FE46AE1DF6AE4A28F2B370EE5F4www.aboutcookies.org/-/media/images... https://www.aboutcookies.org/-/media/images/campaigns/aboutcookies/249131_aboutcookies_option2_standard_image_card_695x358_eu.png?h=358&w=695&rev=84a63244506d49a4866552cadcf3f896&hash=D0039FE46AE1DF6AE4A28F2B370EE5F4 — 200 — 64.7 KiB — 112 ms — h3https://www.aboutcookies.org/assets/js/index.js?v=20260418003154www.aboutcookies.org/assets/js/inde... https://www.aboutcookies.org/assets/js/index.js?v=20260418003154 — 200 — 299.2 KiB — 119 ms — h3https://www.aboutcookies.org/assets/img/blank.png?timestamp=1776798005542www.aboutcookies.org/assets/img/bla... https://www.aboutcookies.org/assets/img/blank.png?timestamp=1776798005542 — 200 — 717 B — 83 ms — h3https://www.googletagmanager.com/gtag/js?id=G-463CHWS42G&cx=c&gtm=4e64h1www.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-463CHWS42G&cx=c&gtm=4e64h1 — 200 — 144.3 KiB — 49 ms — h2https://www.google-analytics.com/analytics.jswww.google-analytics.com/analytics.... https://www.google-analytics.com/analytics.js — 200 — 20.9 KiB — 79 ms — h2https://region1.google-analytics.com/g/collect?v=2&tid=G-463CHWS42G&gtm=45je64h1v9117424870z879138653za20gzb79138653zd79138653&_p=1776798005355&gcs=G100&gcd=13p3pPl2l5l1&npa=1&dma_cps=-&dma=1&are=1&cid=669956943.1776798006&frm=0&pscdl=denied&rcb=6&sr=800x600&uaa=x86&uab=64&uafvl=Chromium%3B147.0.7727.101%7CNot.A%252FBrand%3B8.0.0.0&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115616986~115938466~115938468~117266400~118128922~118463261&sid=1776798005&sct=1&seg=0&dl=https%3A%2F%2Fwww.aboutcookies.org%2F&dt=About%20Cookies&en=page_view&_fv=1&_nsi=1&_ss=1&ep.primaryTag=&ep.pagePublishDate=20210810&ep.pageModifiedDate=20251013&ep.author=&ep.pageTopics=&ep.pageSectors=&ep.pageServices=&ep.pageCampaigns=&ep.referrer=&ep.Page%20Path=%2F&up.userType=Anonymous&up.userLanguage=&up.userOrganisation=&up.userSectors=&up.userServices=&up.userTopics=&up.userRegions=&tfd=667region1.google-analytics.com/g/coll... https://region1.google-analytics.com/g/collect?v=2&tid=G-463CHWS42G&gtm=45je64h1v9117424870z879138653za20gzb79138653zd79138653&_p=1776798005355&gcs=G100&gcd=13p3pPl2l5l1&npa=1&dma_cps=-&dma=1&are=1&cid=669956943.1776798006&frm=0&pscdl=denied&rcb=6&sr=800x600&uaa=x86&uab=64&uafvl=Chromium%3B147.0.7727.101%7CNot.A%252FBrand%3B8.0.0.0&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115616986~115938466~115938468~117266400~118128922~118463261&sid=1776798005&sct=1&seg=0&dl=https%3A%2F%2Fwww.aboutcookies.org%2F&dt=About%20Cookies&en=page_view&_fv=1&_nsi=1&_ss=1&ep.primaryTag=&ep.pagePublishDate=20210810&ep.pageModifiedDate=20251013&ep.author=&ep.pageTopics=&ep.pageSectors=&ep.pageServices=&ep.pageCampaigns=&ep.referrer=&ep.Page%20Path=%2F&up.userType=Anonymous&up.userLanguage=&up.userOrganisation=&up.userSectors=&up.userServices=&up.userTopics=&up.userRegions=&tfd=667 — 204 — 552 B — 66 ms — h2https://www.aboutcookies.org/assets/img/favicon/favicon.ico?v=20260418003154www.aboutcookies.org/assets/img/fav... https://www.aboutcookies.org/assets/img/favicon/favicon.ico?v=20260418003154 — 200 — 3.3 KiB — 68 ms — h3https://dc.services.visualstudio.com/v2/trackdc.services.visualstudio.com/v2/tra... https://dc.services.visualstudio.com/v2/track — 204 — 0 B — 201 ms — h2https://dc.services.visualstudio.com/v2/trackdc.services.visualstudio.com/v2/tra... https://dc.services.visualstudio.com/v2/track — 439 — 327 B — 31 ms — h2
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 338ms · 476KB · £5/mo
www.aboutcookies.org
Other
Optional
Execution 136ms
Transfer 32 KB
Monthly Cost £2/mo
www.aboutcookies.org
Other
Optional
Execution 84ms
Transfer 299 KB
Unused 75%
Monthly Cost £1/mo
Unattributable
Other
Optional
Execution 67ms
Transfer 0 KB
Monthly Cost £1/mo
Google Tag Manager
Tag Manager
Optional
Execution 52ms
Transfer 144 KB
Unused 44%
Monthly Cost £1/mo

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

75% of www.aboutcookies.org'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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