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https://britishmuseum.org

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
69
GRADE
D
FIX
6
REVIEW
1
PASS
8
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.
76
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
81
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
92
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.

3.35 s

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

14.03 s

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

4.64 s

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

0.021

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

5.62 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.

19.68 s

Page Load Progression

758 ms
1.5 s
2.3 s
3.0 s
3.8 s
4.5 s
5.3 s
6.1 s
Checks
17
8 PASS 1 REVIEW 6 FIX
F
Page Weight Budget
Action
12.6 MB transferred, 49 requests
FIX
12.6 MB transferred, 49 requests
Critical::
Page weighs 16.0 MB (12.6 MB transferred)
Warning::
JavaScript is 1.5 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.5 MB
Info::
49 HTTP requests
Info::
Estimated 2.6 g CO2 per page load
12.6 MB / 2.4 MB budget
12.6 MB transferred
49 requests
2.6 g CO2 per page load
Other 10.3 MiB 82%
JavaScript 1.5 MiB 12%
Images 549.3 KiB 4%
Fonts 124.7 KiB 1%
CSS 45.9 KiB 0%
HTML 34.3 KiB 0%
Other 2.2 KiB 0%
Other 1.6 KiB 0%
Other 959 B 0%
Other 637 B 0%
0 2.4 MB 4.9 MB
Over 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

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 (12.6 MiB of 12.6 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Execution Cost
Action
12543ms total JS execution
FIX
12543ms total JS execution
Warning::
https://consent.cookiebot.com/uc.js: 7225ms CPU time
Warning::
https://www.britishmuseum.org/: 1140ms CPU time
Warning::
Unattributable: 861ms CPU time
Warning::
https://www.britishmuseum.org/sites/default/files/...: 684ms CPU time
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-MW5...: 635ms CPU time
Warning::
Third-party scripts: 12543ms (100% of total)

Main Thread Breakdown

Script Evaluation 40% Parse HTML & CSS 35% Other 12% Style & Layout 5% Script Parsing & Compilation 5%
ScriptTotalScriptingParse/CompileParty
https://consent.cookiebot.com/uc.js7225ms2712ms18ms3rd
https://www.britishmuseum.org/1140ms54ms5ms3rd
Unattributable861ms18ms0ms3rd
https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw684ms237ms43ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-MW5VCK635ms536ms88ms3rd
https://www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1495ms423ms67ms3rd
https://www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js405ms392ms4ms3rd
https://www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h1214ms159ms53ms3rd
https://consent.cookiebot.com/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&referer=www.britishmuseum.org&dnt=false&init=false&framework=TCFv2.3202ms47ms154ms3rd
https://www.googletagmanager.com/gtag/js?id=AW-869763654&cx=c&gtm=4e64h1187ms136ms49ms3rd

Showing top 10 of 14 scripts

F
JS Bundles
Action
16 scripts, 574 KB unused
FIX
16 scripts, 574 KB unused
Warning::
https://www.britishmuseum.org/sites/default/files/...: 75 KB unused (68%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-MW5...: 74 KB unused (39%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/destination?...: 66 KB unused (38%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://consent.cookiebot.com/Framework/IAB/consen...: 64 KB unused (73%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=AW-869...: 64 KB unused (44%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 574 KB
574 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw112 KB75 KB (68%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-MW5VCK190 KB74 KB (39%)✓3rd
https://www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1174 KB66 KB (38%)✓3rd
https://consent.cookiebot.com/Framework/IAB/consent-sdk-2.3.js88 KB64 KB (73%)✓3rd
https://www.googletagmanager.com/gtag/js?id=AW-869763654&cx=c&gtm=4e64h1144 KB64 KB (44%)✓3rd
https://www.googletagmanager.com/gtag/js?id=AW-967338294&cx=c&gtm=4e64h1144 KB64 KB (44%)✓3rd
https://www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h1144 KB63 KB (44%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-8361401&cx=c&gtm=4e64h1130 KB61 KB (47%)✓3rd
https://consent.cookiebot.com/uc.js36 KB22 KB (62%)✓3rd
https://consent.cookiebot.com/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&referer=www.britishmuseum.org&dnt=false&init=false&framework=TCFv2.3298 KB21 KB (7%)✓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

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

F
Page Weight Inventory
Action
49 resources · 12.6 MB · 574 KB savings available
FIX
49 resources · 12.6 MB · 574 KB savings available
Warning::
Page weight 11.6 MB over 1MB target
Got: 12.6 MB Expected: ≤ 1 MB
Info::
~574 KB of savings available
Warning::
48 third-party resources (100% of weight)
Info::
2 resources over 200KB
49 resources · 12.6 MiB · 48 third-party 11.6 MiB over 1MB target
Media 82% · 10.3 MiB
JavaScript 12% · 1.5 MiB
Image 4% · 551.1 KiB
Font 1% · 124.7 KiB
CSS 0% · 45.9 KiB
Document 0% · 34.3 KiB
Other 0% · 3.5 KiB

~574.4 KiB of savings available

Remove unused JavaScript: 574.4 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
Image Optimization
13 images, 0 KB saveable
REVIEW
13 images, 0 KB saveable
Info::
All images are well-optimized
13 images 549 KB
0 oversized -0 KB
7 legacy format
0 missing dimensions CLS risk
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
3 fonts (125 KB)
PASS
3 fonts (125 KB)
Info::
3 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

3

125 KB total

Render-blocking

0

of 3

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 FCP 3.3 s LCP 14.0 shttps://www.britishmuseum.org/themes/custom/numiko/dist/font/30be5afa71f98fd86158.woff230be5afa71f98fd86158.woff2 https://www.britishmuseum.org/themes/custom/numiko/dist/font/30be5afa71f98fd86158.woff2 — 41.8 KiB — 20 ms — font-display: swaphttps://www.britishmuseum.org/themes/custom/numiko/dist/font/6ec9f4d567808508ff88.woff26ec9f4d567808508ff88.woff2 https://www.britishmuseum.org/themes/custom/numiko/dist/font/6ec9f4d567808508ff88.woff2 — 41.4 KiB — 20 ms — font-display: swaphttps://www.britishmuseum.org/themes/custom/numiko/dist/font/c299e7cc33987d1c5420.woff2c299e7cc33987d1c5420.woff2 https://www.britishmuseum.org/themes/custom/numiko/dist/font/c299e7cc33987d1c5420.woff2 — 41.5 KiB — 25 ms — font-display: swap
30be5afa71f98fd86158.woff2 woff2 swap
Size 42 KB
Load time 20 ms
Start 224 ms
Risk FOUT — text flashes from fallback to web font
6ec9f4d567808508ff88.woff2 woff2 swap
Size 41 KB
Load time 20 ms
Start 224 ms
Risk FOUT — text flashes from fallback to web font
c299e7cc33987d1c5420.woff2 woff2 swap
Size 41 KB
Load time 25 ms
Start 3.8 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
3 hints, 0 missing preconnects
PASS
3 hints, 0 missing preconnects
Info::
Page uses 3 resource hint(s)

Current Resource Hints

preconnect
3
preload
—
dns-prefetch
—
prefetch
—

3 resource hints configured

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
49 requests over 5939ms
INFO
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s FCP 3.3 s LCP 14.0 shttps://britishmuseum.org// https://britishmuseum.org/ — 301 — 162 B — 18 ms — h3https://www.britishmuseum.org/www.britishmuseum.org/ https://www.britishmuseum.org/ — 200 — 33.5 KiB — 40 ms — h3https://www.britishmuseum.org/sites/default/files/css/css_VsHlxZe888vVcIftkt15QWpKH3V1haCgHBdjKgYED9c.css?delta=0&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S0uqczJzEvXKUotLsjPK84sS40vSUzKSY1Py8wpSS3SR4jrgsUBEDQY4wwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/css/css_VsHlxZe888vVcIftkt15QWpKH3V1haCgHBdjKgYED9c.css?delta=0&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S0uqczJzEvXKUotLsjPK84sS40vSUzKSY1Py8wpSS3SR4jrgsUBEDQY4w — 200 — 590 B — 20 ms — h3https://www.britishmuseum.org/sites/default/files/css/css_qv6dCFGN2Vda1nUS7_s-LrSxyqnB-FqQ7tSNlUhAAWY.css?delta=1&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S0uqczJzEvXKUotLsjPK84sS40vSUzKSY1Py8wpSS3SR4jrgsUBEDQY4wwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/css/css_qv6dCFGN2Vda1nUS7_s-LrSxyqnB-FqQ7tSNlUhAAWY.css?delta=1&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S0uqczJzEvXKUotLsjPK84sS40vSUzKSY1Py8wpSS3SR4jrgsUBEDQY4w — 200 — 44.3 KiB — 32 ms — h3https://www.britishmuseum.org/sites/default/files/js/js_SLwwA2J3XCQ_1HHbqjZARtcKpH5ptrNw6AYNvCtkz0I.js?scope=header&delta=0&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkwwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/js/js_SLwwA2J3XCQ_1HHbqjZARtcKpH5ptrNw6AYNvCtkz0I.js?scope=header&delta=0&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw — 200 — 1.3 KiB — 29 ms — h3https://www.britishmuseum.org/themes/custom/numiko/dist/img/british-museum-logo.svgwww.britishmuseum.org/themes/custom... https://www.britishmuseum.org/themes/custom/numiko/dist/img/british-museum-logo.svg — 200 — 3.0 KiB — 30 ms — h3https://www.britishmuseum.org/sites/default/files/styles/1_1_media_small/public/2019-10/Great%20Court%2004.jpg?h=b771c6d0&itok=zzSdgfuNwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/1_1_media_small/public/2019-10/Great%20Court%2004.jpg?h=b771c6d0&itok=zzSdgfuN — 200 — 101.6 KiB — 31 ms — h3https://www.britishmuseum.org/sites/default/files/styles/16_9_media_small/public/2026-02/Bayeux_Tapestry_teaser_1920x1080.jpg?h=57ddbe17&itok=Q64QK0zswww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/16_9_media_small/public/2026-02/Bayeux_Tapestry_teaser_1920x1080.jpg?h=57ddbe17&itok=Q64QK0zs — 200 — 81.2 KiB — 32 ms — h3https://www.britishmuseum.org/sites/default/files/styles/16_9_media_small/public/2025-09/Hawaii_teaser_1920x1080.jpg?h=91e50914&itok=u6LfrpJ4www.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/16_9_media_small/public/2025-09/Hawaii_teaser_1920x1080.jpg?h=91e50914&itok=u6LfrpJ4 — 200 — 77.8 KiB — 24 ms — h3https://www.britishmuseum.org/sites/default/files/styles/16_9_media_small/public/2025-10/Samurai_teaser_2000x1160px.jpg?h=c34677e7&itok=y2h8cTInwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/16_9_media_small/public/2025-10/Samurai_teaser_2000x1160px.jpg?h=c34677e7&itok=y2h8cTIn — 200 — 41.0 KiB — 34 ms — h3https://www.britishmuseum.org/core/assets/vendor/jquery/jquery.min.js?v=4.0.0www.britishmuseum.org/core/assets/v... https://www.britishmuseum.org/core/assets/vendor/jquery/jquery.min.js?v=4.0.0 — 200 — 31.8 KiB — 70 ms — h3https://www.britishmuseum.org/core/misc/drupalSettingsLoader.js?v=11.3.7www.britishmuseum.org/core/misc/dru... https://www.britishmuseum.org/core/misc/drupalSettingsLoader.js?v=11.3.7 — 200 — 838 B — 27 ms — h3https://www.britishmuseum.org/core/misc/drupal.js?v=11.3.7www.britishmuseum.org/core/misc/dru... https://www.britishmuseum.org/core/misc/drupal.js?v=11.3.7 — 200 — 7.6 KiB — 53 ms — h3https://www.britishmuseum.org/core/misc/drupal.init.js?v=11.3.7www.britishmuseum.org/core/misc/dru... https://www.britishmuseum.org/core/misc/drupal.init.js?v=11.3.7 — 200 — 957 B — 53 ms — h3https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkwwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw — 200 — 111.8 KiB — 74 ms — h3https://consent.cookiebot.com/uc.jsconsent.cookiebot.com/uc.js https://consent.cookiebot.com/uc.js — 200 — 35.7 KiB — 131 ms — h2https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2019-10/Inspired%20by%20The%20British%20Museum.jpg?itok=BdXHDRg_www.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2019-10/Inspired%20by%20The%20British%20Museum.jpg?itok=BdXHDRg_ — 200 — 41.2 KiB — 34 ms — h3https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Lewis-chessmen-shop_edit.jpg?itok=EdOavAvFwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Lewis-chessmen-shop_edit.jpg?itok=EdOavAvF — 200 — 23.4 KiB — 69 ms — h3https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Sutton-Hoo-Helmet.jpg?itok=wpqcxtfLwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Sutton-Hoo-Helmet.jpg?itok=wpqcxtfL — 200 — 38.5 KiB — 66 ms — h3https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Coloursplash%20London%20Tea%20Towel_edit.jpg?itok=gS-QjFSWwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Coloursplash%20London%20Tea%20Towel_edit.jpg?itok=gS-QjFSW — 200 — 60.8 KiB — 73 ms — 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https://pagead2.googlesyndication.com/ccm/collect?rcb=2&frm=0&en=page_view&dl=https%3A%2F%2Fwww.britishmuseum.org%2F&scrsrc=www.googletagmanager.com&rnd=1957514094.1776806987&navt=n&npa=1&us_privacy=1YNY&gdpr=1&gdpr_consent=tcempty&gdid=dMWZhNz&_tu=CA&gtm=45be64h1v896453182z871766321za20gzb71766321zd71766321xec&gcs=G100&gcd=13q3p3q3q5l1&dma_cps=-&dma=1&tcfd=1265a&tag_exp=0~115616986~115938466~115938469~117266401&apve=1&apvf=f&apvc=0&tids=AW-869763654&tid=AW-869763654&tft=1776806987205&tfd=995 — 200 — 21 B — 37 ms — h3https://pagead2.googlesyndication.com/ccm/collect?rcb=15&frm=0&en=page_view&dl=https%3A%2F%2Fwww.britishmuseum.org%2F&scrsrc=www.googletagmanager.com&rnd=1957514094.1776806987&navt=n&npa=1&us_privacy=1YNY&gdpr=1&gdpr_consent=tcempty&gdid=dMWZhNz&_tu=CA&gtm=45be64h1v9181465908z871766321za20gzb71766321zd71766321xec&gcs=G100&gcd=13q3p3q3q5l1&dma_cps=-&dma=1&tcfd=1265a&tag_exp=0~115938466~115938469~117266401&apve=1&apvf=f&apvc=0&tids=AW-967338294&tid=AW-967338294&tft=1776806987206&tfd=997pagead2.googlesyndication.com/ccm/c... https://pagead2.googlesyndication.com/ccm/collect?rcb=15&frm=0&en=page_view&dl=https%3A%2F%2Fwww.britishmuseum.org%2F&scrsrc=www.googletagmanager.com&rnd=1957514094.1776806987&navt=n&npa=1&us_privacy=1YNY&gdpr=1&gdpr_consent=tcempty&gdid=dMWZhNz&_tu=CA&gtm=45be64h1v9181465908z871766321za20gzb71766321zd71766321xec&gcs=G100&gcd=13q3p3q3q5l1&dma_cps=-&dma=1&tcfd=1265a&tag_exp=0~115938466~115938469~117266401&apve=1&apvf=f&apvc=0&tids=AW-967338294&tid=AW-967338294&tft=1776806987206&tfd=997 — 200 — 21 B — 37 ms — h3https://www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1www.googletagmanager.com/gtag/desti... https://www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1 — 200 — 174.0 KiB — 61 ms — h3https://www.britishmuseum.org/themes/custom/numiko/favicon.icowww.britishmuseum.org/themes/custom... https://www.britishmuseum.org/themes/custom/numiko/favicon.ico — 200 — 1.8 KiB — 22 ms — h3https://www.britishmuseum.org/themes/custom/numiko/dist/font/c299e7cc33987d1c5420.woff2www.britishmuseum.org/themes/custom... https://www.britishmuseum.org/themes/custom/numiko/dist/font/c299e7cc33987d1c5420.woff2 — 200 — 41.5 KiB — 25 ms — h3https://www.google-analytics.com/g/collect?v=2&tid=G-08TLB9R8X1&gtm=45je64h1v885594199z871766321za20gzb71766321zd71766321&_p=1776806986323&gcs=G100&gcd=13q3p3q3q5l1&npa=1&dma_cps=-&dma=0&tcfd=1265g&gdid=dMWZhNz&_eu=EAAAAEA&are=1&cid=1674310220.1776806992&frm=0&ir=1&pscdl=denied&rcb=4&sr=412x823&uaa=&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=moto%20g%20power%20(2022)&uamb=1&uap=Android&uapv=11.0&uaw=0&ul=en-us&_s=1&tag_exp=0~115616985~115938466~115938469~117266401~117384406&sid=1776806990&sct=1&seg=0&dl=https%3A%2F%2Fwww.britishmuseum.org%2F&dt=British%20Museum&_tu=CA&en=page_load_time&_fv=1&_nsi=1&_ss=1&epn.loading_time_sec=2.02&ep.gtm_tag=ga4%20-%20event%20-%20page%20load%20time&tfd=5897www.google-analytics.com/g/collect?... https://www.google-analytics.com/g/collect?v=2&tid=G-08TLB9R8X1&gtm=45je64h1v885594199z871766321za20gzb71766321zd71766321&_p=1776806986323&gcs=G100&gcd=13q3p3q3q5l1&npa=1&dma_cps=-&dma=0&tcfd=1265g&gdid=dMWZhNz&_eu=EAAAAEA&are=1&cid=1674310220.1776806992&frm=0&ir=1&pscdl=denied&rcb=4&sr=412x823&uaa=&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=moto%20g%20power%20(2022)&uamb=1&uap=Android&uapv=11.0&uaw=0&ul=en-us&_s=1&tag_exp=0~115616985~115938466~115938469~117266401~117384406&sid=1776806990&sct=1&seg=0&dl=https%3A%2F%2Fwww.britishmuseum.org%2F&dt=British%20Museum&_tu=CA&en=page_load_time&_fv=1&_nsi=1&_ss=1&epn.loading_time_sec=2.02&ep.gtm_tag=ga4%20-%20event%20-%20page%20load%20time&tfd=5897 — 204 — 553 B — 42 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 12543ms · 1525KB · €136/mo
consent.cookiebot.com
Other
Costly
Execution 7225ms
Transfer 36 KB
Unused 62%
Monthly Cost €78/mo
www.britishmuseum.org
Other
Costly
Execution 1140ms
Transfer 34 KB
Monthly Cost €12/mo
Unattributable
Other
Costly
Execution 861ms
Transfer 0 KB
Monthly Cost €9/mo
www.britishmuseum.org
Other
Costly
Execution 684ms
Transfer 112 KB
Unused 68%
Monthly Cost €7/mo
Google Tag Manager
Tag Manager
Costly
Execution 635ms
Transfer 190 KB
Unused 39%
Monthly Cost €7/mo
Google Tag Manager
Tag Manager
Costly
Execution 495ms
Transfer 174 KB
Unused 38%
Monthly Cost €5/mo
www.britishmuseum.org
Other
Costly
Execution 405ms
Transfer 0 KB
Monthly Cost €4/mo
Google Tag Manager
Tag Manager
Costly
Execution 214ms
Transfer 144 KB
Unused 44%
Monthly Cost €2/mo
consent.cookiebot.com
Other
Costly
Execution 202ms
Transfer 298 KB
Unused 7%
Monthly Cost €2/mo
Google Tag Manager
Tag Manager
Optional
Execution 187ms
Transfer 144 KB
Unused 44%
Monthly Cost €2/mo
Google Tag Manager
Tag Manager
Optional
Execution 185ms
Transfer 144 KB
Unused 44%
Monthly Cost €2/mo
Google Tag Manager
Tag Manager
Optional
Execution 174ms
Transfer 130 KB
Unused 47%
Monthly Cost €2/mo
www.britishmuseum.org
Other
Optional
Execution 73ms
Transfer 32 KB
Monthly Cost €1/mo
consent.cookiebot.com
Other
Optional
Execution 62ms
Transfer 88 KB
Unused 73%
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • consent.cookiebot.com adds 7225ms and costs ~€78/month
  • www.britishmuseum.org adds 1140ms and costs ~€12/month
  • Unattributable adds 861ms and costs ~€9/month
  • www.britishmuseum.org adds 684ms and costs ~€7/month
  • Google Tag Manager adds 635ms and costs ~€7/month
  • Google Tag Manager adds 495ms and costs ~€5/month
  • www.britishmuseum.org adds 405ms and costs ~€4/month
  • Google Tag Manager adds 214ms and costs ~€2/month
  • consent.cookiebot.com adds 202ms and costs ~€2/month

100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.

Why this matters

When third-party JS execution time exceeds your own, performance gains from frontend work are capped by code you don't own.

Learn more ▾

Every millisecond of third-party JS competes with your own for main-thread time. If their share is bigger than yours, optimization on your code base barely moves the needle. Audit, defer, or remove third-parties before further frontend optimization. Use Lighthouse's third-party audit to identify the worst offenders.

Source: web.dev

consent.cookiebot.com takes 7225ms 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

62% of consent.cookiebot.com'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.britishmuseum.org takes 1140ms 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 861ms 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.britishmuseum.org takes 684ms 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

68% of www.britishmuseum.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

Google Tag Manager takes 635ms 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 495ms 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.britishmuseum.org takes 405ms 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 214ms 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

consent.cookiebot.com takes 202ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

73% of consent.cookiebot.com'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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