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Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
71
GRADE
C
FIX
5
REVIEW
3
PASS
7
INFO
2

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

Mobile Desktop
38
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
95
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.

3.01 s

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

9.51 s

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

1.98 s

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

0.019

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

5.31 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.

21.52 s

Page Load Progression

375 ms
750 ms
1.1 s
1.5 s
1.9 s
2.2 s
2.6 s
3.0 s
Checks
17
7 PASS 3 REVIEW 5 FIX
F
Page Weight Budget
Action
4.7 MB transferred, 124 requests
FIX
4.7 MB transferred, 124 requests
Critical::
Page weighs 21.9 MB (4.7 MB transferred)
Warning::
JavaScript is 2.1 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 2.1 MB
Warning::
Images are 2.0 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 2.0 MB
Warning::
124 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.99 g CO2 per page load
4.7 MB / 2.4 MB budget
4.7 MB transferred
124 requests
0.99 g CO2 per page load
JavaScript 2.1 MiB 45%
Images 2.0 MiB 42%
HTML 342.8 KiB 7%
Fonts 142.6 KiB 3%
CSS 116.6 KiB 2%
Other 41.2 KiB 1%
Other 4.2 KiB 0%
Other 844 B 0%
Other 726 B 0%
Other 0 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

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Why this matters

Image bandwidth is high — modern formats (WebP/AVIF) and resizing typically cut it 50%+.

Source: web.dev

Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.

Why this matters

High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.

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 (4.7 MiB of 4.7 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Execution Cost
Action
4445ms total JS execution
FIX
4445ms total JS execution
Warning::
https://www.bfi.org.uk/dist/client/header.3d71a25a...: 2221ms CPU time
Warning::
Unattributable: 772ms CPU time
Warning::
https://www.bfi.org.uk/: 490ms CPU time
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-TPS...: 291ms CPU time
Warning::
https://cookie-cdn.cookiepro.com/scripttemplates/6...: 270ms CPU time
Warning::
Third-party scripts: 4445ms (100% of total)

Main Thread Breakdown

Script Evaluation 65% Other 18% Style & Layout 6% Script Parsing & Compilation 5%
ScriptTotalScriptingParse/CompileParty
https://www.bfi.org.uk/dist/client/header.3d71a25a335fdeada447.js2221ms2052ms47ms3rd
Unattributable772ms115ms0ms3rd
https://www.bfi.org.uk/490ms7ms27ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-TPS5SNQ291ms217ms36ms3rd
https://cookie-cdn.cookiepro.com/scripttemplates/6.34.0/otBannerSdk.js270ms190ms34ms3rd
https://www.bfi.org.uk/dist/client/main.35f4e4ddf81dfc0d5a66.js261ms196ms53ms3rd
https://loader.wisepops.com/get-loader.js?v=1&site=vhfQzVz3qj89ms78ms5ms3rd
https://www.bfi.org.uk/dist/client/458.6fecf68cf57238bed5e0.js51ms34ms16ms3rd
D
Page Weight Inventory
Action
124 resources · 4.7 MB · 275 KB savings available
FIX
124 resources · 4.7 MB · 275 KB savings available
Warning::
Page weight 3.7 MB over 1MB target
Got: 4.7 MB Expected: ≤ 1 MB
Info::
~275 KB of savings available
Warning::
123 third-party resources (100% of weight)
Info::
6 resources over 200KB
124 resources · 4.7 MiB · 123 third-party 3.7 MiB over 1MB target
JavaScript 45% · 2.1 MiB
Image 42% · 2.0 MiB
Document 7% · 342.8 KiB
Font 3% · 142.6 KiB
CSS 3% · 121.3 KiB
Other 0% · 20.1 KiB

~275.4 KiB of savings available

Remove unused JavaScript: 275.4 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.

C
Image Optimization
Action
29 images, 0 KB saveable
REVIEW
29 images, 0 KB saveable
Warning::
https://core-cms.bfi.org.uk/sites/default/files/st... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://core-cms.bfi.org.uk/sites/default/files/st... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
29 images 2.0 MB
0 oversized -0 KB
25 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

Performance issues directly impact user engagement and conversion rates.

C
JS Bundles
Action
37 scripts, 275 KB unused
REVIEW
37 scripts, 275 KB unused
Warning::
https://www.bfi.org.uk/dist/client/main.35f4e4ddf8...: 82 KB unused (39%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.bfi.org.uk/dist/client/header.3d71a25a...: 80 KB unused (46%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-TPS...: 71 KB unused (47%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://cookie-cdn.cookiepro.com/scripttemplates/6...: 43 KB unused (51%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 275 KB
275 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.bfi.org.uk/dist/client/main.35f4e4ddf81dfc0d5a66.js213 KB82 KB (39%)✓3rd
https://www.bfi.org.uk/dist/client/header.3d71a25a335fdeada447.js173 KB80 KB (46%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-TPS5SNQ151 KB71 KB (47%)✓3rd
https://cookie-cdn.cookiepro.com/scripttemplates/6.34.0/otBannerSdk.js83 KB43 KB (51%)✓3rd
https://www.youtube.com/s/_/ytembeds/_/js/k=ytembeds.base.en_US.5f0apfZzpOA.2021.O/am=AAAABA/d=1/br=1/rs=AGKMywFg3MG1UeKh8ePjbhY_YEMv-NHjmA/m=root,base0 KB—✓3rd
https://www.youtube.com/s/_/ytembeds/_/js/k=ytembeds.base.en_US.5f0apfZzpOA.2021.O/am=AAAABA/d=1/exm=base,root/ed=1/br=1/rs=AGKMywFg3MG1UeKh8ePjbhY_YEMv-NHjmA/m=r78Drb0 KB—✓3rd
https://www.bfi.org.uk/dist/client/221.ca8a0580ca295700de76.js5 KB—✓3rd
https://www.bfi.org.uk/dist/client/855.89bf89ff8df193b3087b.js14 KB—✓3rd
https://www.bfi.org.uk/dist/client/457.21f7c1b616af2cd49187.js5 KB—✓3rd
https://www.bfi.org.uk/dist/client/458.6fecf68cf57238bed5e0.js45 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

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Text Compression
All text resources are compressed
PASS
All text resources are compressed
Info::
All text resources are compressed
All text resources are properly compressed.
A+
Font Loading
7 fonts (143 KB)
PASS
7 fonts (143 KB)
Info::
7 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

7

143 KB total

Render-blocking

0

of 7

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 5.0 s 6.0 s 7.0 s 8.0 s 9.0 s FCP 3.0 s LCP 9.5 shttps://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2memvYaGs126MiZpBA-UvWbX... https://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2 — 42.0 KiB — 45 ms — font-display: swaphttps://www.bfi.org.uk/dist/client/a69ce9c0d611d0866111.woff2a69ce9c0d611d0866111.woff2 https://www.bfi.org.uk/dist/client/a69ce9c0d611d0866111.woff2 — 27.6 KiB — 195 ms — font-display: swaphttps://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 33.9 KiB — 79 ms — font-display: swaphttps://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 0 B — 86 ms — font-display: swaphttps://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 0 B — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBA.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBA.woff2 — 39.2 KiB — 43 ms — font-display: swaphttps://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBA.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBA.woff2 — 0 B — 42 ms — font-display: swap
memvYaGs126MiZpBA-UvWbX... woff2 swap
Size 42 KB
Load time 45 ms
Start 285 ms
Risk FOUT — text flashes from fallback to web font
a69ce9c0d611d0866111.woff2 woff2 swap
Size 28 KB
Load time 195 ms
Start 744 ms
Risk FOUT — text flashes from fallback to web font
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 34 KB
Load time 79 ms
Start 948 ms
Risk FOUT — text flashes from fallback to web font
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 0 KB
Load time 86 ms
Start 949 ms
Risk FOUT — text flashes from fallback to web font
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 0 KB
Load time 0 ms
Start 1.4 s
Risk FOUT — text flashes from fallback to web font
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 39 KB
Load time 43 ms
Start 1.8 s
Risk FOUT — text flashes from fallback to web font
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 0 KB
Load time 42 ms
Start 1.8 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
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
A+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
Network Waterfall
124 requests over 5023ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s 6.0 s 7.0 s 8.0 s 9.0 s FCP 3.0 s LCP 9.5 shttps://bfi.org.uk// https://bfi.org.uk/ — 301 — 257 B — 10 ms — h2https://www.bfi.org.uk/www.bfi.org.uk/ https://www.bfi.org.uk/ — 200 — 74.9 KiB — 14 ms — h2https://cookie-cdn.cookiepro.com/scripttemplates/otSDKStub.jscookie-cdn.cookiepro.com/scripttemp... https://cookie-cdn.cookiepro.com/scripttemplates/otSDKStub.js — 200 — 9.3 KiB — 101 ms — h2https://fonts.googleapis.com/css?family=Open+Sans:400,600,700&display=swapfonts.googleapis.com/css?family=Ope... https://fonts.googleapis.com/css?family=Open+Sans:400,600,700&display=swap — 200 — 2.2 KiB — 114 ms — h2https://www.bfi.org.uk/dist/client/main.91accebbcdc09556dc84.csswww.bfi.org.uk/dist/client/main.91a... https://www.bfi.org.uk/dist/client/main.91accebbcdc09556dc84.css — 200 — 859 B — 4 ms — h2https://www.bfi.org.uk/dist/client/header.91accebbcdc09556dc84.csswww.bfi.org.uk/dist/client/header.9... https://www.bfi.org.uk/dist/client/header.91accebbcdc09556dc84.css — 200 — 929 B — 5 ms — h2https://www.bfi.org.uk/dist/client/0207614d447715c2d2b9.svgwww.bfi.org.uk/dist/client/0207614d... https://www.bfi.org.uk/dist/client/0207614d447715c2d2b9.svg — 200 — 1.4 KiB — 367 ms — h2https://www.bfi.org.uk/dist/client/e51a86bb7ce82a9e9741.svgwww.bfi.org.uk/dist/client/e51a86bb... https://www.bfi.org.uk/dist/client/e51a86bb7ce82a9e9741.svg — 200 — 1.5 KiB — 214 ms — h2https://cookie-cdn.cookiepro.com/consent/bd6dd4ce-0e1b-4bd8-b05b-5376972199ca/bd6dd4ce-0e1b-4bd8-b05b-5376972199ca.jsoncookie-cdn.cookiepro.com/consent/bd... https://cookie-cdn.cookiepro.com/consent/bd6dd4ce-0e1b-4bd8-b05b-5376972199ca/bd6dd4ce-0e1b-4bd8-b05b-5376972199ca.json — 200 — 2.5 KiB — 83 ms — h2https://hello.myfonts.net/count/3bb155hello.myfonts.net/count/3bb155 https://hello.myfonts.net/count/3bb155 — 200 — 373 B — 107 ms — h2https://www.bfi.org.uk/dist/client/header.3d71a25a335fdeada447.jswww.bfi.org.uk/dist/client/header.3... https://www.bfi.org.uk/dist/client/header.3d71a25a335fdeada447.js — 200 — 173.4 KiB — 188 ms — h3https://core-cms.bfi.org.uk/sites/default/files/styles/responsive/public/2020-07/bfiplayer-white.png/400x0/bfiplayer-white.pngcore-cms.bfi.org.uk/sites/default/f... https://core-cms.bfi.org.uk/sites/default/files/styles/responsive/public/2020-07/bfiplayer-white.png/400x0/bfiplayer-white.png — 200 — 3.1 KiB — 141 ms — h2https://core-cms.bfi.org.uk/sites/default/files/styles/responsive/public/2023-01/sight-and-sound-logo-black-300x93.png/400x0/sight-and-sound-logo-black-300x93.pngcore-cms.bfi.org.uk/sites/default/f... https://core-cms.bfi.org.uk/sites/default/files/styles/responsive/public/2023-01/sight-and-sound-logo-black-300x93.png/400x0/sight-and-sound-logo-black-300x93.png — 200 — 6.8 KiB — 138 ms — h2https://www.bfi.org.uk/dist/client/main.35f4e4ddf81dfc0d5a66.jswww.bfi.org.uk/dist/client/main.35f... https://www.bfi.org.uk/dist/client/main.35f4e4ddf81dfc0d5a66.js — 200 — 212.5 KiB — 625 ms — h3https://www.googletagmanager.com/gtm.js?id=GTM-TPS5SNQwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-TPS5SNQ — 200 — 150.9 KiB — 194 ms — h2https://geolocation.onetrust.com/cookieconsentpub/v1/geo/locationgeolocation.onetrust.com/cookiecons... https://geolocation.onetrust.com/cookieconsentpub/v1/geo/location — 200 — 281 B — 108 ms — h2https://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2fonts.gstatic.com/s/opensans/v44/me... https://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2 — 200 — 42.0 KiB — 45 ms — h3https://cookie-cdn.cookiepro.com/scripttemplates/6.34.0/otBannerSdk.jscookie-cdn.cookiepro.com/scripttemp... https://cookie-cdn.cookiepro.com/scripttemplates/6.34.0/otBannerSdk.js — 200 — 83.2 KiB — 44 ms — h2https://www.youtube.com/embed/2AVisfWtgTs?feature=oembed&cc_load_policy=1www.youtube.com/embed/2AVisfWtgTs?f... https://www.youtube.com/embed/2AVisfWtgTs?feature=oembed&cc_load_policy=1 — -1 — 0 B — 211 ms — https://www.youtube.com/embed/h4s11I82Ofk?feature=oembed&cc_load_policy=1www.youtube.com/embed/h4s11I82Ofk?f... https://www.youtube.com/embed/h4s11I82Ofk?feature=oembed&cc_load_policy=1 — 200 — 56.6 KiB — 233 ms — h2https://www.youtube.com/embed/SrmUFHdxxHE?feature=oembed&cc_load_policy=1www.youtube.com/embed/SrmUFHdxxHE?f... https://www.youtube.com/embed/SrmUFHdxxHE?feature=oembed&cc_load_policy=1 — 200 — 54.0 KiB — 229 ms — h2https://core-cms.bfi.org.uk/sites/default/files/styles/responsive/public/2026-03/raging-bull-1980-de-niro-in-boxing-ring-punch-homepage-crop.jpg/1920x1080/raging-bull-1980-de-niro-in-boxing-ring-punch-homepage-crop.jpgcore-cms.bfi.org.uk/sites/default/f... 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h2https://www.youtube.com/generate_204?MNnHpgwww.youtube.com/generate_204?MNnHpg https://www.youtube.com/generate_204?MNnHpg — 204 — 10 B — 30 ms — h3https://www.youtube.com/generate_204?YSuTzwwww.youtube.com/generate_204?YSuTzw https://www.youtube.com/generate_204?YSuTzw — 204 — 10 B — 31 ms — h3https://jnn-pa.googleapis.com/$rpc/google.internal.waa.v1.Waa/GenerateITjnn-pa.googleapis.com/$rpc/google.i... https://jnn-pa.googleapis.com/$rpc/google.internal.waa.v1.Waa/GenerateIT — 200 — 189 B — 36 ms — h2https://jnn-pa.googleapis.com/$rpc/google.internal.waa.v1.Waa/GenerateITjnn-pa.googleapis.com/$rpc/google.i... https://jnn-pa.googleapis.com/$rpc/google.internal.waa.v1.Waa/GenerateIT — 200 — 145 B — 34 ms — h3https://activity.wisepops.com/?v=2.1.136&site=vhfQzVz3qjactivity.wisepops.com/?v=2.1.136&si... https://activity.wisepops.com/?v=2.1.136&site=vhfQzVz3qj — 200 — 0 B — 197 ms — h2https://activity.wisepops.com/?v=2.1.136&site=vhfQzVz3qjactivity.wisepops.com/?v=2.1.136&si... https://activity.wisepops.com/?v=2.1.136&site=vhfQzVz3qj — 200 — 257 B — 122 ms — h2https://www.youtube.com/youtubei/v1/log_event?alt=jsonwww.youtube.com/youtubei/v1/log_eve... https://www.youtube.com/youtubei/v1/log_event?alt=json — 200 — 50 B — 43 ms — h3https://www.youtube.com/youtubei/v1/log_event?alt=jsonwww.youtube.com/youtubei/v1/log_eve... https://www.youtube.com/youtubei/v1/log_event?alt=json — 200 — 50 B — 40 ms — h3https://www.youtube.com/youtubei/v1/log_event?alt=jsonwww.youtube.com/youtubei/v1/log_eve... https://www.youtube.com/youtubei/v1/log_event?alt=json — 200 — 50 B — 44 ms — h3
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 4445ms · 740KB · £46/mo
www.bfi.org.uk
Other
Costly
Execution 2221ms
Transfer 173 KB
Unused 46%
Monthly Cost £23/mo
Unattributable
Other
Costly
Execution 772ms
Transfer 0 KB
Monthly Cost £8/mo
www.bfi.org.uk
Other
Costly
Execution 490ms
Transfer 75 KB
Monthly Cost £5/mo
Google Tag Manager
Tag Manager
Costly
Execution 291ms
Transfer 151 KB
Unused 47%
Monthly Cost £3/mo
cookie-cdn.cookiepro.com
Other
Costly
Execution 270ms
Transfer 83 KB
Unused 51%
Monthly Cost £3/mo
www.bfi.org.uk
Other
Costly
Execution 261ms
Transfer 213 KB
Unused 39%
Monthly Cost £3/mo
loader.wisepops.com
Other
Optional
Execution 89ms
Transfer 0 KB
Monthly Cost £1/mo
www.bfi.org.uk
Other
Optional
Execution 51ms
Transfer 45 KB
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • www.bfi.org.uk adds 2221ms and costs ~£23/month
  • Unattributable adds 772ms and costs ~£8/month
  • www.bfi.org.uk adds 490ms and costs ~£5/month
  • Google Tag Manager adds 291ms and costs ~£3/month
  • cookie-cdn.cookiepro.com adds 270ms and costs ~£3/month
  • www.bfi.org.uk adds 261ms and costs ~£3/month

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

Why this matters

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

Learn more ▾

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

Source: web.dev

www.bfi.org.uk takes 2221ms 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 772ms 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.bfi.org.uk takes 490ms 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 291ms 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

cookie-cdn.cookiepro.com 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

51% of cookie-cdn.cookiepro.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.bfi.org.uk 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

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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