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https://cancerresearchuk.org

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
71
GRADE
C
FIX
6
REVIEW
2
PASS
7
INFO
2

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

Mobile Desktop
44
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.
100
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.

2.77 s

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

8.35 s

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

1.27 s

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

0.000

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

4.61 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.

17.27 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 2 REVIEW 6 FIX
F
Page Weight Budget
Action
3.1 MB transferred, 64 requests
FIX
3.1 MB transferred, 64 requests
Warning::
Page weighs 7.4 MB (3.1 MB transferred)
Warning::
JavaScript is 1.8 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.8 MB
Info::
Fonts are 782 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 782 KB
Info::
64 HTTP requests
Info::
Estimated 0.65 g CO2 per page load
3.1 MB / 2.4 MB budget
3.1 MB transferred
64 requests
0.65 g CO2 per page load
JavaScript 1.8 MiB 58%
Fonts 782.0 KiB 24%
Images 382.5 KiB 12%
Other 65.8 KiB 2%
HTML 56.3 KiB 2%
Other 38.3 KiB 1%
CSS 10.9 KiB 0%
Other 3.6 KiB 0%
Other 2.7 KiB 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

Subset fonts to include only used characters, or switch to system font stacks.

Why this matters

Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).

Source: web.dev font loading

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 (3.1 MiB of 3.1 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Execution Cost
Action
3740ms total JS execution
FIX
3740ms total JS execution
Warning::
https://www.cancerresearchuk.org/_next/static/chun...: 767ms CPU time
Warning::
Unattributable: 627ms CPU time
Warning::
https://www.cancerresearchuk.org/_next/static/chun...: 411ms CPU time
Warning::
https://www.cancerresearchuk.org/: 402ms CPU time
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-KHM...: 276ms CPU time
Warning::
Third-party scripts: 3740ms (100% of total)

Main Thread Breakdown

Script Evaluation 61% Other 14% Script Parsing & Compilation 12% Style & Layout 8%
ScriptTotalScriptingParse/CompileParty
https://www.cancerresearchuk.org/_next/static/chunks/18-f78cdf1f90d3fe0f.js767ms717ms19ms3rd
Unattributable627ms113ms0ms3rd
https://www.cancerresearchuk.org/_next/static/chunks/7105-e8c503187482c546.js411ms348ms63ms3rd
https://www.cancerresearchuk.org/402ms15ms21ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-KHMJ7CS276ms226ms44ms3rd
https://www.cancerresearchuk.org/_next/static/chunks/1377-c76d500bf8de9995.js255ms202ms52ms3rd
https://cdn.cookielaw.org/scripttemplates/202411.2.0/otBannerSdk.js243ms148ms35ms3rd
https://www.googletagmanager.com/gtag/js?id=DC-8727222&cx=c&gtm=4e64h1204ms177ms25ms3rd
https://www.googletagmanager.com/gtag/js?id=G-58736Z2GNN&cx=c&gtm=4e64h1200ms148ms51ms3rd
https://www.cancerresearchuk.org/_next/static/chunks/87c73c54-dd8d81ac9604067c.js175ms137ms12ms3rd

Showing top 10 of 12 scripts

F
JS Bundles
Action
28 scripts, 628 KB unused
FIX
28 scripts, 628 KB unused
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-KHM...: 78 KB unused (43%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.cancerresearchuk.org/_next/static/chun...: 77 KB unused (45%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=G-5873...: 77 KB unused (46%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=AW-986...: 65 KB unused (48%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=DC-872...: 64 KB unused (49%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 628 KB
628 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtm.js?id=GTM-KHMJ7CS181 KB78 KB (43%)✓3rd
https://www.cancerresearchuk.org/_next/static/chunks/7180-be8f246206a70c65.js174 KB77 KB (45%)✓3rd
https://www.googletagmanager.com/gtag/js?id=G-58736Z2GNN&cx=c&gtm=4e64h1168 KB77 KB (46%)✓3rd
https://www.googletagmanager.com/gtag/js?id=AW-986083629&cx=c&gtm=4e64h1137 KB65 KB (48%)✓3rd
https://www.googletagmanager.com/gtag/js?id=DC-8727222&cx=c&gtm=4e64h1130 KB64 KB (49%)✓3rd
https://cdn.cookielaw.org/scripttemplates/202411.2.0/otBannerSdk.js113 KB61 KB (54%)✓3rd
https://www.cancerresearchuk.org/_next/static/chunks/2691-38189575cf339bed.js64 KB49 KB (81%)✓3rd
https://www.cancerresearchuk.org/_next/static/chunks/7105-e8c503187482c546.js263 KB46 KB (18%)✓3rd
https://www.cancerresearchuk.org/_next/static/chunks/1377-c76d500bf8de9995.js256 KB42 KB (16%)✓3rd
https://www.cancerresearchuk.org/_next/static/chunks/7693-ddc473c47d5fbf1c.js55 KB37 KB (72%)✓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
64 resources · 3.1 MB · 628 KB savings available
FIX
64 resources · 3.1 MB · 628 KB savings available
Warning::
Page weight 2.1 MB over 1MB target
Got: 3.1 MB Expected: ≤ 1 MB
Info::
~628 KB of savings available
Warning::
63 third-party resources (100% of weight)
Info::
2 resources over 200KB
64 resources · 3.1 MiB · 63 third-party 2.1 MiB over 1MB target
JavaScript 58% · 1.8 MiB
Font 24% · 782.0 KiB
Image 13% · 421.2 KiB
Other 2% · 67.2 KiB
Document 2% · 56.4 KiB
CSS 0% · 15.3 KiB

~628.2 KiB of savings available

Remove unused JavaScript: 628.2 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
9 images, 0 KB saveable
REVIEW
9 images, 0 KB saveable
Warning::
is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
9 images 382 KB
0 oversized -0 KB
3 legacy format
1 missing dimensions CLS risk

Set explicit width and height to prevent CLS.

Why this matters

Performance issues directly impact user engagement and conversion rates.

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
10 fonts (782 KB)
PASS
10 fonts (782 KB)
Info::
10 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

10

782 KB total

Render-blocking

0

of 10

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 FCP 2.8 s LCP 8.3 shttps://www.cancerresearchuk.org/_next/static/media/001e002f03b017c1-s.p.woff001e002f03b017c1-s.p.woff https://www.cancerresearchuk.org/_next/static/media/001e002f03b017c1-s.p.woff — 74.4 KiB — 37 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/22f59f5d5b479322-s.p.woff22f59f5d5b479322-s.p.woff https://www.cancerresearchuk.org/_next/static/media/22f59f5d5b479322-s.p.woff — 143.8 KiB — 43 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/35789c96e49e6b7f-s.p.woff35789c96e49e6b7f-s.p.woff https://www.cancerresearchuk.org/_next/static/media/35789c96e49e6b7f-s.p.woff — 72.6 KiB — 41 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/6eb962549b7dc14e-s.p.woff6eb962549b7dc14e-s.p.woff https://www.cancerresearchuk.org/_next/static/media/6eb962549b7dc14e-s.p.woff — 45.7 KiB — 46 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/72b3d441bbdb517b-s.p.woff72b3d441bbdb517b-s.p.woff https://www.cancerresearchuk.org/_next/static/media/72b3d441bbdb517b-s.p.woff — 44.8 KiB — 41 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/82b68f6f091d46c1-s.p.woff82b68f6f091d46c1-s.p.woff https://www.cancerresearchuk.org/_next/static/media/82b68f6f091d46c1-s.p.woff — 44.6 KiB — 37 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/aac452a0af5508c6-s.p.woffaac452a0af5508c6-s.p.woff https://www.cancerresearchuk.org/_next/static/media/aac452a0af5508c6-s.p.woff — 45.6 KiB — 53 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/bb3853c711608cc5-s.p.woffbb3853c711608cc5-s.p.woff https://www.cancerresearchuk.org/_next/static/media/bb3853c711608cc5-s.p.woff — 69.7 KiB — 43 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/e21fa8781a9a32b3-s.p.woffe21fa8781a9a32b3-s.p.woff https://www.cancerresearchuk.org/_next/static/media/e21fa8781a9a32b3-s.p.woff — 74.9 KiB — 44 ms — font-display: swaphttps://www.cancerresearchuk.org/_next/static/media/fb98212e27cc7064-s.p.wofffb98212e27cc7064-s.p.woff https://www.cancerresearchuk.org/_next/static/media/fb98212e27cc7064-s.p.woff — 166.0 KiB — 62 ms — font-display: swap
001e002f03b017c1-s.p.woff woff swap
Size 74 KB
Load time 37 ms
Start 115 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
22f59f5d5b479322-s.p.woff woff swap
Size 144 KB
Load time 43 ms
Start 116 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
35789c96e49e6b7f-s.p.woff woff swap
Size 73 KB
Load time 41 ms
Start 116 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
6eb962549b7dc14e-s.p.woff woff swap
Size 46 KB
Load time 46 ms
Start 116 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
72b3d441bbdb517b-s.p.woff woff swap
Size 45 KB
Load time 41 ms
Start 116 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
82b68f6f091d46c1-s.p.woff woff swap
Size 45 KB
Load time 37 ms
Start 116 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
aac452a0af5508c6-s.p.woff woff swap
Size 46 KB
Load time 53 ms
Start 117 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
bb3853c711608cc5-s.p.woff woff swap
Size 70 KB
Load time 43 ms
Start 117 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
e21fa8781a9a32b3-s.p.woff woff swap
Size 75 KB
Load time 44 ms
Start 117 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
fb98212e27cc7064-s.p.woff woff swap
Size 166 KB
Load time 62 ms
Start 117 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
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 ~389 KB and ~778 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
15 hints, 0 missing preconnects
PASS
15 hints, 0 missing preconnects
Info::
Page uses 15 resource hint(s)

Current Resource Hints

preconnect
—
preload
+5
15
dns-prefetch
—
prefetch
—

15 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
Network Waterfall
64 requests over 1230ms
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 FCP 2.8 s LCP 8.3 shttps://cancerresearchuk.org// https://cancerresearchuk.org/ — 301 — 91 B — 84 ms — h2https://www.cancerresearchuk.org/www.cancerresearchuk.org/ https://www.cancerresearchuk.org/ — 200 — 56.3 KiB — 16 ms — h2https://www.cancerresearchuk.org/_next/static/media/001e002f03b017c1-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/001e002f03b017c1-s.p.woff — 200 — 74.4 KiB — 37 ms — h2https://www.cancerresearchuk.org/_next/static/media/22f59f5d5b479322-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/22f59f5d5b479322-s.p.woff — 200 — 143.8 KiB — 43 ms — h2https://www.cancerresearchuk.org/_next/static/media/35789c96e49e6b7f-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/35789c96e49e6b7f-s.p.woff — 200 — 72.6 KiB — 41 ms — h2https://www.cancerresearchuk.org/_next/static/media/6eb962549b7dc14e-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/6eb962549b7dc14e-s.p.woff — 200 — 45.7 KiB — 46 ms — h2https://www.cancerresearchuk.org/_next/static/media/72b3d441bbdb517b-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/72b3d441bbdb517b-s.p.woff — 200 — 44.8 KiB — 41 ms — h2https://www.cancerresearchuk.org/_next/static/media/82b68f6f091d46c1-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/82b68f6f091d46c1-s.p.woff — 200 — 44.6 KiB — 37 ms — h2https://www.cancerresearchuk.org/_next/static/media/aac452a0af5508c6-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/aac452a0af5508c6-s.p.woff — 200 — 45.6 KiB — 53 ms — h2https://www.cancerresearchuk.org/_next/static/media/bb3853c711608cc5-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/bb3853c711608cc5-s.p.woff — 200 — 69.7 KiB — 43 ms — h2https://www.cancerresearchuk.org/_next/static/media/e21fa8781a9a32b3-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/e21fa8781a9a32b3-s.p.woff — 200 — 74.9 KiB — 44 ms — h2https://www.cancerresearchuk.org/_next/static/media/fb98212e27cc7064-s.p.woffwww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/media/fb98212e27cc7064-s.p.woff — 200 — 166.0 KiB — 62 ms — h2https://www.cancerresearchuk.org/_next/static/css/c361d1f26b524758.csswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/css/c361d1f26b524758.css — 200 — 3.6 KiB — 14 ms — h2https://www.cancerresearchuk.org/_next/static/css/c682fa5ca7232dbe.csswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/css/c682fa5ca7232dbe.css — 200 — 3.4 KiB — 30 ms — h2https://www.cancerresearchuk.org/_next/static/css/761dc5ff23fcdfa0.csswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/css/761dc5ff23fcdfa0.css — 200 — 3.9 KiB — 32 ms — h2https://www.googletagmanager.com/gtm.js?id=GTM-KHMJ7CSwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-KHMJ7CS — 200 — 181.5 KiB — 197 ms — h2https://cdn.cookielaw.org/scripttemplates/otSDKStub.jscdn.cookielaw.org/scripttemplates/o... https://cdn.cookielaw.org/scripttemplates/otSDKStub.js — 200 — 9.1 KiB — 73 ms — h2https://images.ctfassets.net/u7vsjnoopqo5/4uDzgmkufKEz5N4ef7374L/6418128c52a524c1ffad4a815f68ecee/cruk-logo.svgimages.ctfassets.net/u7vsjnoopqo5/4... https://images.ctfassets.net/u7vsjnoopqo5/4uDzgmkufKEz5N4ef7374L/6418128c52a524c1ffad4a815f68ecee/cruk-logo.svg — 200 — 6.7 KiB — 104 ms — h2https://www.cancerresearchuk.org/_next/image?url=https%3A%2F%2Fimages.ctfassets.net%2Fu7vsjnoopqo5%2F4KvYfwN2xheb6YkPFfL0Re%2F483d435617c31f7394ada12dbed5d7a8%2FDAT-DSC_0678.webp&w=750&q=65www.cancerresearchuk.org/_next/imag... https://www.cancerresearchuk.org/_next/image?url=https%3A%2F%2Fimages.ctfassets.net%2Fu7vsjnoopqo5%2F4KvYfwN2xheb6YkPFfL0Re%2F483d435617c31f7394ada12dbed5d7a8%2FDAT-DSC_0678.webp&w=750&q=65 — 200 — 22.3 KiB — 50 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/webpack-d18f008b72876714.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/webpack-d18f008b72876714.js — 200 — 5.7 KiB — 49 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/87c73c54-dd8d81ac9604067c.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/87c73c54-dd8d81ac9604067c.js — 200 — 57.6 KiB — 74 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/18-f78cdf1f90d3fe0f.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/18-f78cdf1f90d3fe0f.js — 200 — 48.2 KiB — 79 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/main-app-57aa1716f0d0f500.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/main-app-57aa1716f0d0f500.js — 200 — 3.8 KiB — 50 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/7180-be8f246206a70c65.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/7180-be8f246206a70c65.js — 200 — 174.1 KiB — 104 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/7105-e8c503187482c546.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/7105-e8c503187482c546.js — 200 — 262.6 KiB — 105 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/8619-0ff90b77525dda4d.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/8619-0ff90b77525dda4d.js — 200 — 14.5 KiB — 70 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/7852-beba7ef95a6f0242.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/7852-beba7ef95a6f0242.js — 200 — 8.3 KiB — 52 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/3295-faf68d8d3dc812dd.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/3295-faf68d8d3dc812dd.js — 200 — 6.4 KiB — 54 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/2691-38189575cf339bed.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/2691-38189575cf339bed.js — 200 — 63.7 KiB — 101 ms — h2https://www.cancerresearchuk.org/_next/static/chunks/4925-3876f624fa71ddb4.jswww.cancerresearchuk.org/_next/stat... https://www.cancerresearchuk.org/_next/static/chunks/4925-3876f624fa71ddb4.js — 200 — 7.3 KiB — 66 ms — h2
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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
100% of JavaScript execution is third-party
First-party Third-party 3740ms · 1585KB · €60/mo
www.cancerresearchuk.org
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Unattributable
Other
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www.cancerresearchuk.org
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Unused 18%
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www.cancerresearchuk.org
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Google Tag Manager
Tag Manager
Costly
Execution 276ms
Transfer 181 KB
Unused 43%
Monthly Cost €4/mo
www.cancerresearchuk.org
Other
Costly
Execution 255ms
Transfer 256 KB
Unused 16%
Monthly Cost €4/mo
OneTrust
Consent
Essential
Execution 243ms
Transfer 113 KB
Unused 54%
Monthly Cost €4/mo
Google Tag Manager
Tag Manager
Costly
Execution 204ms
Transfer 130 KB
Unused 49%
Monthly Cost €3/mo
Google Tag Manager
Tag Manager
Costly
Execution 200ms
Transfer 168 KB
Unused 46%
Monthly Cost €3/mo
www.cancerresearchuk.org
Other
Optional
Execution 175ms
Transfer 58 KB
Monthly Cost €3/mo
Google Tag Manager
Tag Manager
Optional
Execution 128ms
Transfer 137 KB
Unused 48%
Monthly Cost €2/mo
www.cancerresearchuk.org
Other
Optional
Execution 53ms
Transfer 174 KB
Unused 45%
Monthly Cost €1/mo

These scripts may cost more than they're worth

  • www.cancerresearchuk.org adds 767ms and costs ~€12/month
  • Unattributable adds 627ms and costs ~€10/month
  • www.cancerresearchuk.org adds 411ms and costs ~€7/month
  • www.cancerresearchuk.org adds 402ms and costs ~€6/month
  • Google Tag Manager adds 276ms and costs ~€4/month
  • www.cancerresearchuk.org adds 255ms and costs ~€4/month
  • Google Tag Manager adds 204ms and costs ~€3/month
  • Google Tag Manager adds 200ms 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.cancerresearchuk.org takes 767ms 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 627ms 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.cancerresearchuk.org takes 411ms 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.cancerresearchuk.org takes 402ms 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 276ms 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.cancerresearchuk.org takes 255ms 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

54% of OneTrust'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 204ms 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 200ms 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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