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https://britishmuseum.org

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
69
GRADE
D
FIX
6
REVIEW
1
PASS
6
INFO
2

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

Mobile Desktop
61
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
79
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.

918 ms

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

1.69 s

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

862 ms

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

0.002

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

2.09 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.

4.41 s

Page Load Progression

779 ms
1.6 s
2.3 s
3.1 s
3.9 s
4.7 s
5.5 s
6.2 s
Checks
15
6 PASS 1 REVIEW 6 FIX
F
Page Weight Budget
Action
3.9 MB transferred, 49 requests
FIX
3.9 MB transferred, 49 requests
Warning::
Page weighs 10.4 MB (3.9 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 0.81 g CO2 per page load
3.9 MB / 2.4 MB budget
3.9 MB transferred
49 requests
0.81 g CO2 per page load
JavaScript 1.5 MiB 38%
Other 1.2 MiB 32%
Images 958.4 KiB 24%
Fonts 124.7 KiB 3%
CSS 45.9 KiB 1%
HTML 34.6 KiB 1%
Other 2.2 KiB 0%
Other 1.8 KiB 0%
Other 960 B 0%
Other 84 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 (3.9 MiB of 3.9 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Execution Cost
Action
2974ms total JS execution
FIX
2974ms total JS execution
Warning::
https://consent.cookiebot.com/ec5f4b04-e699-4bea-a...: 1639ms CPU time
Warning::
https://www.britishmuseum.org/: 270ms CPU time
Info::
Unattributable: 243ms CPU time
Info::
https://www.britishmuseum.org/sites/default/files/...: 207ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-MW5...: 181ms CPU time
Warning::
Third-party scripts: 2974ms (100% of total)

Main Thread Breakdown

Script Evaluation 40% Parse HTML & CSS 33% Other 13% Style & Layout 5% Script Parsing & Compilation 5%
ScriptTotalScriptingParse/CompileParty
https://consent.cookiebot.com/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&referer=www.britishmuseum.org&dnt=false&init=false&framework=TCFv2.31639ms537ms39ms3rd
https://www.britishmuseum.org/270ms12ms1ms3rd
Unattributable243ms4ms0ms3rd
https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw207ms69ms11ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-MW5VCK181ms157ms21ms3rd
https://www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1178ms125ms26ms3rd
https://consent.cookiebot.com/uc.js117ms111ms3ms3rd
https://www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js88ms85ms1ms3rd
https://www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h152ms38ms14ms3rd
F
JS Bundles
Action
16 scripts, 595 KB unused
FIX
16 scripts, 595 KB unused
Warning::
https://www.britishmuseum.org/sites/default/files/...: 76 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-967...: 64 KB unused (44%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 595 KB
595 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 KB76 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-967338294&cx=c&gtm=4e64h1144 KB64 KB (44%)✓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-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 · 3.9 MB · 595 KB savings available
FIX
49 resources · 3.9 MB · 595 KB savings available
Warning::
Page weight 2.9 MB over 1MB target
Got: 3.9 MB Expected: ≤ 1 MB
Info::
~595 KB of savings available
Warning::
48 third-party resources (100% of weight)
Info::
4 resources over 200KB
49 resources · 3.9 MiB · 48 third-party 2.9 MiB over 1MB target
JavaScript 38% · 1.5 MiB
Media 32% · 1.2 MiB
Image 24% · 960.2 KiB
Font 3% · 124.7 KiB
CSS 1% · 45.9 KiB
Document 1% · 34.6 KiB
Other 0% · 3.2 KiB

~594.6 KiB of savings available

Remove unused JavaScript: 594.6 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 958 KB
0 oversized -0 KB
8 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 1.0 s 2.0 s 3.0 s 4.0 s FCP 918 ms LCP 1.7 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 — 24 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 — 24 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 — 23 ms — font-display: swap
30be5afa71f98fd86158.woff2 woff2 swap
Size 42 KB
Load time 24 ms
Start 230 ms
Risk FOUT — text flashes from fallback to web font
6ec9f4d567808508ff88.woff2 woff2 swap
Size 41 KB
Load time 24 ms
Start 230 ms
Risk FOUT — text flashes from fallback to web font
c299e7cc33987d1c5420.woff2 woff2 swap
Size 41 KB
Load time 23 ms
Start 3.9 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+
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 4062ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s FCP 918 ms LCP 1.7 shttps://britishmuseum.org// https://britishmuseum.org/ — 301 — 162 B — 41 ms — h3https://www.britishmuseum.org/www.britishmuseum.org/ https://www.britishmuseum.org/ — 200 — 33.8 KiB — 68 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 — 21 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 — 26 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 — 25 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 — 21 ms — h3https://www.britishmuseum.org/sites/default/files/styles/uncropped_large/public/2019-10/Great%20Court%2004.jpg?itok=PKKEIUbnwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_large/public/2019-10/Great%20Court%2004.jpg?itok=PKKEIUbn — 200 — 109.3 KiB — 25 ms — h3https://www.britishmuseum.org/sites/default/files/styles/16_9_media_large/public/2026-02/Bayeux_Tapestry_teaser_1920x1080.jpg?h=57ddbe17&itok=dbI2QmpBwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/16_9_media_large/public/2026-02/Bayeux_Tapestry_teaser_1920x1080.jpg?h=57ddbe17&itok=dbI2QmpB — 200 — 219.0 KiB — 77 ms — h3https://www.britishmuseum.org/sites/default/files/styles/16_9_media_large/public/2025-09/Hawaii_teaser_1920x1080.jpg?h=91e50914&itok=R1qJ0R0Dwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/16_9_media_large/public/2025-09/Hawaii_teaser_1920x1080.jpg?h=91e50914&itok=R1qJ0R0D — 200 — 247.3 KiB — 94 ms — h3https://www.britishmuseum.org/sites/default/files/styles/16_9_media_large/public/2025-10/Samurai_teaser_2000x1160px.jpg?h=c34677e7&itok=oRdKOFEkwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/16_9_media_large/public/2025-10/Samurai_teaser_2000x1160px.jpg?h=c34677e7&itok=oRdKOFEk — 200 — 104.4 KiB — 56 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 — 75 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 — 39 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 — 47 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 — 954 B — 38 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 — 86 ms — h3https://consent.cookiebot.com/uc.jsconsent.cookiebot.com/uc.js https://consent.cookiebot.com/uc.js — 200 — 35.7 KiB — 261 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 — 74 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 — 60 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 — 68 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 — 77 ms — h3https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Japanese%20Cat%20Tea%20Cups_British%20Museum_edit.jpg?itok=XD3nZqMGwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2020-08/Japanese%20Cat%20Tea%20Cups_British%20Museum_edit.jpg?itok=XD3nZqMG — 200 — 9.0 KiB — 63 ms — h3https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2019-10/Inspired%20by%20Hokusai.jpg?itok=asBwnNi5www.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_small/public/2019-10/Inspired%20by%20Hokusai.jpg?itok=asBwnNi5 — 200 — 46.9 KiB — 71 ms — h3https://www.britishmuseum.org/sites/default/files/styles/uncropped_large/public/2019-10/Inspired%20by%20Ancient%20Egypt.jpg?itok=6jEEjhRKwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/styles/uncropped_large/public/2019-10/Inspired%20by%20Ancient%20Egypt.jpg?itok=6jEEjhRK — 200 — 54.9 KiB — 80 ms — h3https://www.googletagmanager.com/gtm.js?id=GTM-MW5VCKwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-MW5VCK — 200 — 189.9 KiB — 86 ms — h2https://www.britishmuseum.org/sites/default/files/css/css_VpCEM3F-0hKPgm5WXV0rtDP5CZ6RXUx9YqaUGOvAUq0.css?delta=2&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S0uqczJzEvXKUotLsjPK84sS40vSUzKSY1Py8wpSS3SR4jrgsUBEDQY4wwww.britishmuseum.org/sites/default... https://www.britishmuseum.org/sites/default/files/css/css_VpCEM3F-0hKPgm5WXV0rtDP5CZ6RXUx9YqaUGOvAUq0.css?delta=2&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S0uqczJzEvXKUotLsjPK84sS40vSUzKSY1Py8wpSS3SR4jrgsUBEDQY4w — 200 — 1.1 KiB — 34 ms — h3https://www.britishmuseum.org/themes/custom/numiko/dist/img/icon-chevron-white.svgwww.britishmuseum.org/themes/custom... 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h3
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https://pagead2.googlesyndication.com/ccm/collect?rcb=5&frm=0&en=page_view&dl=https%3A%2F%2Fwww.britishmuseum.org%2F&scrsrc=www.googletagmanager.com&rnd=1980792561.1776807039&navt=n&npa=1&us_privacy=1YNY&gdpr=1&gdpr_consent=tcempty&gdid=dMWZhNz&_tu=CA&gtm=45fe64h1v9181637325z871766321za20gzb71766321zd71766321xec&gcs=G100&gcd=13q3p3q3q5l1&dma_cps=-&dma=1&tcfd=1265a&tag_exp=0~115616985~115938465~115938469~117266400&apve=1&apvf=f&apvc=0&tids=DC-8361401&tid=DC-8361401&tft=1776807038591&tfd=1617 — 200 — 21 B — 43 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 — 23 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 — 69 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 — 28 ms — h3https://www.google-analytics.com/g/collect?v=2&tid=G-08TLB9R8X1&gtm=45je64h1v885594199z871766321za20gzb71766321zd71766321&_p=1776807037122&gcs=G100&gcd=13q3p3q3q5l1&npa=1&dma_cps=-&dma=0&tcfd=1265g&gdid=dMWZhNz&_eu=EAAAAEA&are=1&cid=937861798.1776807043&frm=0&ir=1&pscdl=denied&rcb=15&sr=800x600&uaa=x86&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115616985~115938465~115938469~117266400&sid=1776807041&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=3.94&ep.gtm_tag=ga4%20-%20event%20-%20page%20load%20time&tfd=6240www.google-analytics.com/g/collect?... https://www.google-analytics.com/g/collect?v=2&tid=G-08TLB9R8X1&gtm=45je64h1v885594199z871766321za20gzb71766321zd71766321&_p=1776807037122&gcs=G100&gcd=13q3p3q3q5l1&npa=1&dma_cps=-&dma=0&tcfd=1265g&gdid=dMWZhNz&_eu=EAAAAEA&are=1&cid=937861798.1776807043&frm=0&ir=1&pscdl=denied&rcb=15&sr=800x600&uaa=x86&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115616985~115938465~115938469~117266400&sid=1776807041&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=3.94&ep.gtm_tag=ga4%20-%20event%20-%20page%20load%20time&tfd=6240 — -1 — 0 B — 0 ms —
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 2974ms · 987KB · €32/mo
consent.cookiebot.com
Other
Costly
Execution 1639ms
Transfer 298 KB
Unused 7%
Monthly Cost €18/mo
www.britishmuseum.org
Other
Costly
Execution 270ms
Transfer 34 KB
Monthly Cost €3/mo
Unattributable
Other
Costly
Execution 243ms
Transfer 0 KB
Monthly Cost €3/mo
www.britishmuseum.org
Other
Costly
Execution 207ms
Transfer 112 KB
Unused 68%
Monthly Cost €2/mo
Google Tag Manager
Tag Manager
Optional
Execution 181ms
Transfer 190 KB
Unused 39%
Monthly Cost €2/mo
Google Tag Manager
Tag Manager
Optional
Execution 178ms
Transfer 174 KB
Unused 38%
Monthly Cost €2/mo
consent.cookiebot.com
Other
Optional
Execution 117ms
Transfer 36 KB
Unused 62%
Monthly Cost €1/mo
www.britishmuseum.org
Other
Optional
Execution 88ms
Transfer 0 KB
Monthly Cost €1/mo
Google Tag Manager
Tag Manager
Optional
Execution 52ms
Transfer 144 KB
Unused 44%
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • consent.cookiebot.com adds 1639ms and costs ~€18/month
  • www.britishmuseum.org adds 270ms and costs ~€3/month
  • Unattributable adds 243ms and costs ~€3/month
  • www.britishmuseum.org adds 207ms 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 1639ms 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 270ms 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 243ms 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 207ms 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

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

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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