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https://tfl.gov.uk

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
77
GRADE
C
FIX
3
REVIEW
2
PASS
10
INFO
2

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

Mobile Desktop
39
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
97
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.
77
SEO Measures basic SEO optimizations: meta tags, crawlability, link text, and mobile friendliness.

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

2.31 s

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

14.32 s

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

1.67 s

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

0.102

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

5.33 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.

14.41 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
10 PASS 2 REVIEW 3 FIX
F
JS Execution Cost
Action
6337ms total JS execution
FIX
6337ms total JS execution
Warning::
https://consent.cookiebot.com/uc.js: 4442ms CPU time
Warning::
https://tfl.gov.uk/cdn/static/scripts/core/min/glo...: 738ms CPU time
Warning::
https://tfl.gov.uk/: 482ms CPU time
Info::
Unattributable: 205ms CPU time
Info::
https://consent.cookiebot.com/e601acc6-2e6f-4bed-a...: 146ms CPU time
Warning::
Third-party scripts: 4929ms (78% of total)

Main Thread Breakdown

Parse HTML & CSS 43% Script Evaluation 35% Style & Layout 8% Other 6% Script Parsing & Compilation 6%
ScriptTotalScriptingParse/CompileParty
https://consent.cookiebot.com/uc.js4442ms1576ms11ms3rd
https://tfl.gov.uk/cdn/static/scripts/core/min/global.min.846723f5.js738ms376ms142ms1st
https://tfl.gov.uk/482ms16ms9ms1st
Unattributable205ms5ms0ms3rd
https://consent.cookiebot.com/e601acc6-2e6f-4bed-a826-046477b39b61/cc.js?renew=false&referer=tfl.gov.uk&dnt=false&init=false&framework=TCFv2.3146ms23ms122ms3rd
https://assets.adobedtm.com/launch-ENc5e3f827edc94f2a816110524598acd7.min.js136ms70ms19ms3rd
https://tfl.gov.uk/cdn/static/scripts/core/min/init.min.347d0889.js125ms96ms3ms1st
https://tfl.gov.uk/cdn/static/scripts/jquery/1.12.4/jquery.min.js64ms39ms9ms1st
F
JS Bundles
Action
19 scripts, 461 KB unused
FIX
19 scripts, 461 KB unused
Warning::
https://tfl.gov.uk/cdn/static/scripts/core/min/glo...: 244 KB unused (78%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://tfl.gov.uk/cdn/static/scripts/core/min/glo...: unminified — 111 KB could be saved
Warning::
https://translate.googleapis.com/_/translate_http/...: 109 KB unused (92%)
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://consent.cookiebot.com/uc.js: 22 KB unused (63%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://consent.cookiebot.com/e601acc6-2e6f-4bed-a...: 21 KB unused (7%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 461 KB
461 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://tfl.gov.uk/cdn/static/scripts/core/min/global.min.846723f5.js313 KB244 KB (78%)✗1st
https://translate.googleapis.com/_/translate_http/_/js/k=translate_http.tr.es.eNjH1Jo6ldQ.O/am=AAAAAQ/d=1/exm=el_conf/ed=1/rs=AN8SPfq_osd-q7vwQm5aouAQRZibUmx4sg/m=el_main119 KB109 KB (92%)✓3rd
https://consent.cookiebot.com/Framework/IAB/consent-sdk-2.3.js88 KB64 KB (73%)✓3rd
https://consent.cookiebot.com/uc.js36 KB22 KB (63%)✓3rd
https://consent.cookiebot.com/e601acc6-2e6f-4bed-a826-046477b39b61/cc.js?renew=false&referer=tfl.gov.uk&dnt=false&init=false&framework=TCFv2.3300 KB21 KB (7%)✓3rd
https://tfl.gov.uk/cdn/static/scripts/jquery/1.12.4/jquery.min.js46 KB—✗1st
https://tfl.gov.uk/cdn/static/scripts//plugins/includes/knockout-2.3.0.min.js19 KB—✓1st
https://assets.adobedtm.com/extensions/EP31dbb9c60e404ba1aa6e746d49be6f29/AppMeasurement_Module_ActivityMap.min.js2 KB—✓3rd
https://tfl.gov.uk/cdn/static/scripts/plugins/smart-banner/smartbanner.js4 KB—✓1st
https://tfl.gov.uk/cdn/static/scripts/jquery/jquery.xdomainrequest.js1 KB—✓1st

Consider code splitting or tree shaking to reduce unused code.

Why this matters

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

Source: web.dev / Lighthouse coverage

Consider code splitting or tree shaking to reduce unused code.

Why this matters

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

Source: web.dev / Lighthouse coverage

Consider code splitting or tree shaking to reduce unused code.

Why this matters

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

Source: web.dev / Lighthouse coverage

Consider code splitting or tree shaking to reduce unused code.

Why this matters

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

Source: web.dev / Lighthouse coverage

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
49 resources · 2.0 MB · 461 KB savings available
FIX
49 resources · 2.0 MB · 461 KB savings available
Warning::
Page weight 1.0 MB over 1MB target
Got: 2.0 MB Expected: ≤ 1 MB
Info::
~461 KB of savings available
Info::
14 third-party resources (31% of weight)
Info::
3 resources over 200KB
49 resources · 2.0 MiB · 14 third-party 1.0 MiB over 1MB target
JavaScript 51% · 1.0 MiB
Image 28% · 571.1 KiB
CSS 15% · 299.2 KiB
Font 5% · 96.5 KiB
Document 1% · 26.5 KiB
Other 0% · 8.1 KiB

~460.5 KiB of savings available

Remove unused JavaScript: 460.5 KiB
C
Page Weight Budget
Action
2.0 MB transferred, 49 requests
REVIEW
2.0 MB transferred, 49 requests
Info::
Page weighs 6.1 MB (2.0 MB transferred)
Warning::
JavaScript is 1.0 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.0 MB
Info::
CSS is 299 KB — consider purging unused styles
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
Got: 299 KB
Info::
49 HTTP requests
Info::
Estimated 0.42 g CO2 per page load
2.0 MB / 2.4 MB budget
2.0 MB transferred
49 requests
0.42 g CO2 per page load
JavaScript 1.0 MiB 51%
Images 569.8 KiB 28%
CSS 299.2 KiB 15%
Fonts 96.5 KiB 5%
HTML 24.3 KiB 1%
Other 10.2 KiB 0%
Other 1.3 KiB 0%
0 2.4 MB 4.9 MB
Approaching limit

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Why this matters

JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.

Source: web.dev

Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.

Why this matters

CSS bundle is large — purge unused styles (PurgeCSS, Tailwind JIT) to reduce CSS payload.

Source: web.dev

C
Image Optimization
Action
11 images, 0 KB saveable
REVIEW
11 images, 0 KB saveable
Warning::
https://tfl.gov.uk/cdn/static/cms/images/promos/tf... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://tfl.gov.uk/static/cms/images/MoL.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
11 images 570 KB
0 oversized -0 KB
11 legacy format
2 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

A
Third-Party Impact
31% third-party, 0 ms blocking
PASS
31% third-party, 0 ms blocking
Info::
Third-party code accounts for 31% of page weight (633.5 KiB of 2.0 MiB)
Info::
Third-party blocking time is low (0 ms)
69%
31%
First-party Third-party
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
4 fonts (97 KB)
PASS
4 fonts (97 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

97 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 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s FCP 2.3 s LCP 14.3 shttps://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Light.woff2Johnston100-Light.woff2 https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Light.woff2 — 21.0 KiB — 38 ms — font-display: swaphttps://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Regular.woff2Johnston100-Regular.woff2 https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Regular.woff2 — 20.3 KiB — 46 ms — font-display: swaphttps://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Medium.woff2Johnston100-Medium.woff2 https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Medium.woff2 — 20.6 KiB — 44 ms — font-display: swaphttps://tfl.gov.uk/static/1/assets/fonts/njfontsigning-medium.woffnjfontsigning-medium.woff https://tfl.gov.uk/static/1/assets/fonts/njfontsigning-medium.woff — 34.7 KiB — 36 ms — font-display: swap
Johnston100-Light.woff2 woff2 swap
Size 21 KB
Load time 38 ms
Start 275 ms
Risk FOUT — text flashes from fallback to web font
Johnston100-Regular.woff2 woff2 swap
Size 20 KB
Load time 46 ms
Start 275 ms
Risk FOUT — text flashes from fallback to web font
Johnston100-Medium.woff2 woff2 swap
Size 21 KB
Load time 44 ms
Start 276 ms
Risk FOUT — text flashes from fallback to web font
njfontsigning-medium.woff woff swap
Size 35 KB
Load time 36 ms
Start 583 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
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)

Fixing the unchecked items could save ~10 KB and ~20 ms

A+
Resource Caching
All resources properly cached
PASS
All resources properly cached
Info::
No caching issues found
All static resources have appropriate caching headers.
A+
Critical Rendering Path
No render-blocking resources
PASS
No render-blocking resources
Info::
No render-blocking resources detected
A+
Resource Hints
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
A+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
A+
Green Hosting
Whether the site is served from green-energy infrastructure
PASS

Green Hosting

This site is hosted on green energy infrastructure

Provider: Cloudflare

A+
HTTP Caching
max-age=60 (1 minute)
PASS
max-age=60 (1 minute)
Info::
Cache-Control header is set
Got: public, must-revalidate, max-age=60, s-maxage=60
Info::
Effective TTL: 1 minute (max-age=60)
Info::
CDN TTL: 1 minute (s-maxage=60)
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

public, must-revalidate, max-age=60, s-maxage=60

DirectiveValueMeaning
public—Any cache may store this response
must-revalidate—Must recheck with server after expiry
max-age60Cache for 1 minute
s-maxage60CDN caches for 1 minute
Effective TTL: 60 seconds
Network Waterfall
49 requests over 3794ms
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 2.3 s LCP 14.3 shttps://tfl.gov.uk// https://tfl.gov.uk/ — 200 — 23.5 KiB — 104 ms — h2https://consent.cookiebot.com/uc.jsconsent.cookiebot.com/uc.js https://consent.cookiebot.com/uc.js — 200 — 35.7 KiB — 51 ms — h2https://assets.adobedtm.com/launch-ENc5e3f827edc94f2a816110524598acd7.min.jsassets.adobedtm.com/launch-ENc5e3f8... https://assets.adobedtm.com/launch-ENc5e3f827edc94f2a816110524598acd7.min.js — 200 — 38.4 KiB — 46 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/small.min.1d5963c4.css/cdn/static/styles/core/min/small.m... https://tfl.gov.uk/cdn/static/styles/core/min/small.min.1d5963c4.css — 200 — 91.5 KiB — 59 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/modules.min.a75e2042.css/cdn/static/styles/core/min/modules... https://tfl.gov.uk/cdn/static/styles/core/min/modules.min.a75e2042.css — 200 — 82.9 KiB — 71 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/specifics-small.min.252ae3e0.css/cdn/static/styles/core/min/specifi... https://tfl.gov.uk/cdn/static/styles/core/min/specifics-small.min.252ae3e0.css — 200 — 85.2 KiB — 77 ms — h2https://tfl.gov.uk/cdn/static/cms/images/promos/tfl-go-hp_rdax_400x200.png/cdn/static/cms/images/promos/tfl-g... https://tfl.gov.uk/cdn/static/cms/images/promos/tfl-go-hp_rdax_400x200.png — 200 — 20.7 KiB — 81 ms — h2https://tfl.gov.uk/cdn/static/cms/images/promos/pom-pom-london-tfl-collection_rdax_400x200.png/cdn/static/cms/images/promos/pom-p... https://tfl.gov.uk/cdn/static/cms/images/promos/pom-pom-london-tfl-collection_rdax_400x200.png — 200 — 93.9 KiB — 81 ms — h2https://tfl.gov.uk/cdn/static/cms/images/promos/bank-closure-700x350_rdax_400x200s.jpg/cdn/static/cms/images/promos/bank-... https://tfl.gov.uk/cdn/static/cms/images/promos/bank-closure-700x350_rdax_400x200s.jpg — 200 — 36.9 KiB — 36 ms — h2https://tfl.gov.uk/static/cms/images/MoL.png/static/cms/images/MoL.png https://tfl.gov.uk/static/cms/images/MoL.png — 200 — 1.8 KiB — 38 ms — h2https://tfl.gov.uk/static/cms/images/GLA_Logo.png/static/cms/images/GLA_Logo.png https://tfl.gov.uk/static/cms/images/GLA_Logo.png — 200 — 2.0 KiB — 38 ms — h2https://tfl.gov.uk/cdn/static/scripts/core/min/init.min.347d0889.js/cdn/static/scripts/core/min/init.m... https://tfl.gov.uk/cdn/static/scripts/core/min/init.min.347d0889.js — 200 — 10.6 KiB — 48 ms — h2https://translate.google.com/translate_a/element.js?cb=googleTranslateElementInittranslate.google.com/translate_a/el... https://translate.google.com/translate_a/element.js?cb=googleTranslateElementInit — 200 — 28.3 KiB — 131 ms — h2https://tfl.gov.uk/cdn/static/scripts/jquery/1.12.4/jquery.min.js/cdn/static/scripts/jquery/1.12.4/j... https://tfl.gov.uk/cdn/static/scripts/jquery/1.12.4/jquery.min.js — 200 — 46.5 KiB — 49 ms — h2https://tfl.gov.uk/cdn/static/scripts/plugins/smart-banner/smartbanner.js/cdn/static/scripts/plugins/smart-b... https://tfl.gov.uk/cdn/static/scripts/plugins/smart-banner/smartbanner.js — 200 — 4.4 KiB — 39 ms — h2https://tfl.gov.uk/cdn/static/images/MoL-small.png/cdn/static/images/MoL-small.png https://tfl.gov.uk/cdn/static/images/MoL-small.png — 200 — 1.4 KiB — 42 ms — h2https://assets.adobedtm.com/extensions/EP31dbb9c60e404ba1aa6e746d49be6f29/AppMeasurement.min.jsassets.adobedtm.com/extensions/EP31... https://assets.adobedtm.com/extensions/EP31dbb9c60e404ba1aa6e746d49be6f29/AppMeasurement.min.js — 200 — 13.0 KiB — 9 ms — h2https://assets.adobedtm.com/extensions/EP31dbb9c60e404ba1aa6e746d49be6f29/AppMeasurement_Module_ActivityMap.min.jsassets.adobedtm.com/extensions/EP31... https://assets.adobedtm.com/extensions/EP31dbb9c60e404ba1aa6e746d49be6f29/AppMeasurement_Module_ActivityMap.min.js — 200 — 1.8 KiB — 7 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/medium.min.cc9ff121.css/cdn/static/styles/core/min/medium.... https://tfl.gov.uk/cdn/static/styles/core/min/medium.min.cc9ff121.css — 200 — 20.1 KiB — 48 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/large.min.c085d741.css/cdn/static/styles/core/min/large.m... https://tfl.gov.uk/cdn/static/styles/core/min/large.min.c085d741.css — 200 — 12.3 KiB — 40 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/print.min.2dbbc696.css/cdn/static/styles/core/min/print.m... https://tfl.gov.uk/cdn/static/styles/core/min/print.min.2dbbc696.css — 200 — 2.6 KiB — 45 ms — h2https://tfl.gov.uk/static/1/images/vsprite_x2.34614087.png/static/1/images/vsprite_x2.3461408... https://tfl.gov.uk/static/1/images/vsprite_x2.34614087.png — 200 — 249.3 KiB — 49 ms — h2https://tfl.gov.uk/static/1/images/vsprite.17114d90.png/static/1/images/vsprite.17114d90.p... https://tfl.gov.uk/static/1/images/vsprite.17114d90.png — 200 — 106.0 KiB — 41 ms — h2https://tfl.gov.uk/static/1/images/homepage_sprite_x2.png/static/1/images/homepage_sprite_x2... https://tfl.gov.uk/static/1/images/homepage_sprite_x2.png — 200 — 24.7 KiB — 35 ms — h2https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Light.woff2/cdn/static/assets/fonts/Johnston10... https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Light.woff2 — 200 — 21.0 KiB — 38 ms — h2https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Regular.woff2/cdn/static/assets/fonts/Johnston10... https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Regular.woff2 — 200 — 20.3 KiB — 46 ms — h2https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Medium.woff2/cdn/static/assets/fonts/Johnston10... https://tfl.gov.uk/cdn/static/assets/fonts/Johnston100-Medium.woff2 — 200 — 20.6 KiB — 44 ms — h2https://tfl.gov.uk/cdn/static/scripts/core/min/global.min.846723f5.js/cdn/static/scripts/core/min/global... https://tfl.gov.uk/cdn/static/scripts/core/min/global.min.846723f5.js — 200 — 312.6 KiB — 61 ms — h2https://tfl.gov.uk/cdn/static/scripts/jquery/jquery.xdomainrequest.js/cdn/static/scripts/jquery/jquery.x... https://tfl.gov.uk/cdn/static/scripts/jquery/jquery.xdomainrequest.js — 200 — 1.4 KiB — 39 ms — h2https://tfl.gov.uk/cdn/static/scripts//plugins/includes/jquery.signalR-2.2.0.min.js/cdn/static/scripts//plugins/includ... https://tfl.gov.uk/cdn/static/scripts//plugins/includes/jquery.signalR-2.2.0.min.js — 200 — 14.6 KiB — 47 ms — h2
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s FCP 2.3 s LCP 14.3 shttps://tfl.gov.uk// https://tfl.gov.uk/ — 200 — 23.5 KiB — 104 ms — h2https://consent.cookiebot.com/uc.jsconsent.cookiebot.com/uc.js https://consent.cookiebot.com/uc.js — 200 — 35.7 KiB — 51 ms — h2https://assets.adobedtm.com/launch-ENc5e3f827edc94f2a816110524598acd7.min.jsassets.adobedtm.com/launch-ENc5e3f8... https://assets.adobedtm.com/launch-ENc5e3f827edc94f2a816110524598acd7.min.js — 200 — 38.4 KiB — 46 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/small.min.1d5963c4.css/cdn/static/styles/core/min/small.m... https://tfl.gov.uk/cdn/static/styles/core/min/small.min.1d5963c4.css — 200 — 91.5 KiB — 59 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/modules.min.a75e2042.css/cdn/static/styles/core/min/modules... https://tfl.gov.uk/cdn/static/styles/core/min/modules.min.a75e2042.css — 200 — 82.9 KiB — 71 ms — h2https://tfl.gov.uk/cdn/static/styles/core/min/specifics-small.min.252ae3e0.css/cdn/static/styles/core/min/specifi... https://tfl.gov.uk/cdn/static/styles/core/min/specifics-small.min.252ae3e0.css — 200 — 85.2 KiB — 77 ms — h2https://tfl.gov.uk/cdn/static/cms/images/promos/tfl-go-hp_rdax_400x200.png/cdn/static/cms/images/promos/tfl-g... https://tfl.gov.uk/cdn/static/cms/images/promos/tfl-go-hp_rdax_400x200.png — 200 — 20.7 KiB — 81 ms — h2https://tfl.gov.uk/cdn/static/cms/images/promos/pom-pom-london-tfl-collection_rdax_400x200.png/cdn/static/cms/images/promos/pom-p... https://tfl.gov.uk/cdn/static/cms/images/promos/pom-pom-london-tfl-collection_rdax_400x200.png — 200 — 93.9 KiB — 81 ms — h2https://tfl.gov.uk/cdn/static/cms/images/promos/bank-closure-700x350_rdax_400x200s.jpg/cdn/static/cms/images/promos/bank-... https://tfl.gov.uk/cdn/static/cms/images/promos/bank-closure-700x350_rdax_400x200s.jpg — 200 — 36.9 KiB — 36 ms — h2https://tfl.gov.uk/static/cms/images/MoL.png/static/cms/images/MoL.png https://tfl.gov.uk/static/cms/images/MoL.png — 200 — 1.8 KiB — 38 ms — h2https://tfl.gov.uk/static/cms/images/GLA_Logo.png/static/cms/images/GLA_Logo.png https://tfl.gov.uk/static/cms/images/GLA_Logo.png — 200 — 2.0 KiB — 38 ms — h2https://tfl.gov.uk/cdn/static/scripts/core/min/init.min.347d0889.js/cdn/static/scripts/core/min/init.m... https://tfl.gov.uk/cdn/static/scripts/core/min/init.min.347d0889.js — 200 — 10.6 KiB — 48 ms — h2https://translate.google.com/translate_a/element.js?cb=googleTranslateElementInittranslate.google.com/translate_a/el... https://translate.google.com/translate_a/element.js?cb=googleTranslateElementInit — 200 — 28.3 KiB — 131 ms — h2https://tfl.gov.uk/cdn/static/scripts/jquery/1.12.4/jquery.min.js/cdn/static/scripts/jquery/1.12.4/j... https://tfl.gov.uk/cdn/static/scripts/jquery/1.12.4/jquery.min.js — 200 — 46.5 KiB — 49 ms — 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HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
78% of JavaScript execution is third-party
First-party Third-party 4929ms · 374KB · £51/mo
consent.cookiebot.com
Other
Costly
Execution 4442ms
Transfer 36 KB
Unused 63%
Monthly Cost £46/mo
Unattributable
Other
Costly
Execution 205ms
Transfer 0 KB
Monthly Cost £2/mo
consent.cookiebot.com
Other
Optional
Execution 146ms
Transfer 300 KB
Unused 7%
Monthly Cost £2/mo
assets.adobedtm.com
Other
Optional
Execution 136ms
Transfer 38 KB
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • consent.cookiebot.com adds 4442ms and costs ~£46/month
  • Unattributable adds 205ms and costs ~£2/month

78% 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 4442ms 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

63% 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

Unattributable takes 205ms 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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