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https://service.gov.uk

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
93
GRADE
A
FIX
2
REVIEW
2
PASS
9
INFO
2

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

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

563 ms

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

653 ms

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

0 ms

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.

563 ms

Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.

655 ms

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
15
9 PASS 2 REVIEW 2 FIX
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 (196.5 KiB of 196.7 KiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
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
6 images, 0 KB saveable
REVIEW
6 images, 0 KB saveable
Info::
All images are well-optimized
6 images 24 KB
0 oversized -0 KB
6 legacy format
0 missing dimensions CLS risk
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
197 KB transferred, 18 requests
PASS
197 KB transferred, 18 requests
Info::
Page weighs 753 KB (197 KB transferred)
Info::
18 HTTP requests
Info::
Estimated 0.04 g CO2 per page load
197 KB / 2.4 MB budget
197 KB transferred
18 requests
0.04 g CO2 per page load
Fonts 64.1 KiB 33%
JavaScript 55.1 KiB 28%
CSS 38.7 KiB 20%
Images 24.2 KiB 12%
HTML 13.3 KiB 7%
Other 1.3 KiB 1%
0 2.4 MB 4.9 MB
Under budget
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+
JS Execution Cost
54ms total JS execution
PASS
54ms total JS execution
Info::
https://www.gov.uk/: 54ms CPU time
Warning::
Third-party scripts: 54ms (100% of total)

Main Thread Breakdown

Other 39% Style & Layout 27% Script Evaluation 22% Rendering 6% Parse HTML & CSS 5%
ScriptTotalScriptingParse/CompileParty
https://www.gov.uk/54ms2ms0ms3rd
A+
Font Loading
2 fonts (64 KB)
PASS
2 fonts (64 KB)
Info::
2 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

2

64 KB total

Render-blocking

0

of 2

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 500 ms 1.0 s FCP 563 ms LCP 653 mshttps://www.gov.uk/assets/frontend/bold-b542beb274-v2-35bf540bb39615b6a517986f3aa83f7fefa1efd1878603eeeb196488078542d1.woff2bold-b542beb274-v2-35bf... https://www.gov.uk/assets/frontend/bold-b542beb274-v2-35bf540bb39615b6a517986f3aa83f7fefa1efd1878603eeeb196488078542d1.woff2 — 31.1 KiB — 25 ms — font-display: swaphttps://www.gov.uk/assets/frontend/light-94a07e06a1-v2-01565b0034e61d4609689bbb7ae0be844701f3812c8fe029fa1659b7ef3aa94f.woff2light-94a07e06a1-v2-015... https://www.gov.uk/assets/frontend/light-94a07e06a1-v2-01565b0034e61d4609689bbb7ae0be844701f3812c8fe029fa1659b7ef3aa94f.woff2 — 33.0 KiB — 23 ms — font-display: swap
bold-b542beb274-v2-35bf... woff2 swap
Size 31 KB
Load time 25 ms
Start 105 ms
Risk FOUT — text flashes from fallback to web font
light-94a07e06a1-v2-015... woff2 swap
Size 33 KB
Load time 23 ms
Start 105 ms
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+
JS Bundles
5 scripts, 26 KB unused
PASS
5 scripts, 26 KB unused
Warning::
https://www.gov.uk/assets/frontend/application-527...: 26 KB unused (63%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 26 KB
26 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.gov.uk/assets/frontend/application-527c564759ff9aa7cb6e6b9fd78dc91ee7add2454050e3a6c441e53d9db254ba.js41 KB26 KB (63%)✓3rd
https://www.gov.uk/assets/frontend/govuk_publishing_components/vendor/lux/lux-measurer-d66192b1b665d415e1874e49a48138b7ae339548aa6cdb8687c7f9933e72b969.js1 KB—✓3rd
https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-custom-data-b9e1806d1da2fa8ef1855d01aa71ba5eb0afc010dd2c4de3672cc7c7a39b0c8c.js0 KB—✓3rd
https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-loader-a65b10e18ceeba3bd8a2eac507c7f2c513cdc82f35097df903fdea87f1dc2e33.js0 KB—✓3rd
https://www.gov.uk/assets/frontend/govuk_publishing_components/load-analytics-79a977bd852f5a521fd985f15017e47a032bab5cc877b5ac11678a2d40d99f49.js12 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

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
Page Weight Inventory
18 resources · 197 KB · 26 KB savings available
PASS
18 resources · 197 KB · 26 KB savings available
Info::
Within 1MB page-weight target
Got: 197 KB
Warning::
17 third-party resources (100% of weight)
18 resources · 196.7 KiB · 17 third-party Within 1MB page-weight target
Font 33% · 64.1 KiB
JavaScript 28% · 55.1 KiB
CSS 20% · 38.7 KiB
Image 13% · 25.4 KiB
Document 7% · 13.3 KiB
Other 0% · 136 B

~25.9 KiB of savings available

Remove unused JavaScript: 25.9 KiB
Network Waterfall
18 requests over 149ms
INFO
0 ms 200 ms 400 ms 600 ms FCP 563 ms LCP 653 mshttps://service.gov.uk// https://service.gov.uk/ — 302 — 136 B — 6 ms — h2https://www.gov.uk/www.gov.uk/ https://www.gov.uk/ — 200 — 13.3 KiB — 7 ms — h2https://www.gov.uk/assets/frontend/views/_homepage-64a9f4f542bbda5bcdae1df09ea442583c3981460eb5cd3be12e18ba1885ba31.csswww.gov.uk/assets/frontend/views/_h... https://www.gov.uk/assets/frontend/views/_homepage-64a9f4f542bbda5bcdae1df09ea442583c3981460eb5cd3be12e18ba1885ba31.css — 200 — 1.6 KiB — 3 ms — h2https://www.gov.uk/assets/frontend/govuk_publishing_components/vendor/lux/lux-measurer-d66192b1b665d415e1874e49a48138b7ae339548aa6cdb8687c7f9933e72b969.jswww.gov.uk/assets/frontend/govuk_pu... https://www.gov.uk/assets/frontend/govuk_publishing_components/vendor/lux/lux-measurer-d66192b1b665d415e1874e49a48138b7ae339548aa6cdb8687c7f9933e72b969.js — 200 — 834 B — 4 ms — h2https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-custom-data-b9e1806d1da2fa8ef1855d01aa71ba5eb0afc010dd2c4de3672cc7c7a39b0c8c.jswww.gov.uk/assets/frontend/govuk_pu... https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-custom-data-b9e1806d1da2fa8ef1855d01aa71ba5eb0afc010dd2c4de3672cc7c7a39b0c8c.js — 200 — 290 B — 2 ms — h2https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-loader-a65b10e18ceeba3bd8a2eac507c7f2c513cdc82f35097df903fdea87f1dc2e33.jswww.gov.uk/assets/frontend/govuk_pu... https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-loader-a65b10e18ceeba3bd8a2eac507c7f2c513cdc82f35097df903fdea87f1dc2e33.js — 200 — 460 B — 3 ms — h2https://www.gov.uk/assets/frontend/govuk_publishing_components/load-analytics-79a977bd852f5a521fd985f15017e47a032bab5cc877b5ac11678a2d40d99f49.jswww.gov.uk/assets/frontend/govuk_pu... https://www.gov.uk/assets/frontend/govuk_publishing_components/load-analytics-79a977bd852f5a521fd985f15017e47a032bab5cc877b5ac11678a2d40d99f49.js — 200 — 12.3 KiB — 10 ms — h3https://www.gov.uk/assets/frontend/application-6e85cd8055c5001deff4f2121849990c359f2e9ce33f89c8e7e6bca2afaf323c.csswww.gov.uk/assets/frontend/applicat... https://www.gov.uk/assets/frontend/application-6e85cd8055c5001deff4f2121849990c359f2e9ce33f89c8e7e6bca2afaf323c.css — 200 — 37.1 KiB — 9 ms — h3https://www.gov.uk/assets/frontend/application-527c564759ff9aa7cb6e6b9fd78dc91ee7add2454050e3a6c441e53d9db254ba.jswww.gov.uk/assets/frontend/applicat... https://www.gov.uk/assets/frontend/application-527c564759ff9aa7cb6e6b9fd78dc91ee7add2454050e3a6c441e53d9db254ba.js — 200 — 41.3 KiB — 10 ms — h3https://www.gov.uk/assets/frontend/govuk_publishing_components/icon-close-eecb5fdf67d1688ddf2f93e6e09d5f87b9b24e0fc53596ad2a65cf187c2c7c76.svgwww.gov.uk/assets/frontend/govuk_pu... https://www.gov.uk/assets/frontend/govuk_publishing_components/icon-close-eecb5fdf67d1688ddf2f93e6e09d5f87b9b24e0fc53596ad2a65cf187c2c7c76.svg — 200 — 515 B — 3 ms — h3https://www.gov.uk/assets/frontend/govuk-crest-9f82a3631d8ac5feb4660345a2b44ca98f077b48248f2cc139a0f412355bebef.svgwww.gov.uk/assets/frontend/govuk-cr... https://www.gov.uk/assets/frontend/govuk-crest-9f82a3631d8ac5feb4660345a2b44ca98f077b48248f2cc139a0f412355bebef.svg — 200 — 14.6 KiB — 3 ms — h3https://www.gov.uk/assets/frontend/bold-b542beb274-v2-35bf540bb39615b6a517986f3aa83f7fefa1efd1878603eeeb196488078542d1.woff2www.gov.uk/assets/frontend/bold-b54... https://www.gov.uk/assets/frontend/bold-b542beb274-v2-35bf540bb39615b6a517986f3aa83f7fefa1efd1878603eeeb196488078542d1.woff2 — 200 — 31.1 KiB — 25 ms — h3https://www.gov.uk/assets/frontend/light-94a07e06a1-v2-01565b0034e61d4609689bbb7ae0be844701f3812c8fe029fa1659b7ef3aa94f.woff2www.gov.uk/assets/frontend/light-94... https://www.gov.uk/assets/frontend/light-94a07e06a1-v2-01565b0034e61d4609689bbb7ae0be844701f3812c8fe029fa1659b7ef3aa94f.woff2 — 200 — 33.0 KiB — 23 ms — h3https://www.gov.uk/assets/frontend/homepage/travel-advice-blue-icon-featured-a03f6981ba9d86e6b84ecfe7bb28557dad14cf00b5270082cd3d3e264e6e63e0.pngwww.gov.uk/assets/frontend/homepage... https://www.gov.uk/assets/frontend/homepage/travel-advice-blue-icon-featured-a03f6981ba9d86e6b84ecfe7bb28557dad14cf00b5270082cd3d3e264e6e63e0.png — 200 — 1.1 KiB — 15 ms — h3https://www.gov.uk/assets/frontend/homepage/register-to-vote-featured-69de22ff8962dcce8f8ebe40a1155a39cc04a6525c0d8e21e68fe5bfd01ee2f5.pngwww.gov.uk/assets/frontend/homepage... https://www.gov.uk/assets/frontend/homepage/register-to-vote-featured-69de22ff8962dcce8f8ebe40a1155a39cc04a6525c0d8e21e68fe5bfd01ee2f5.png — 200 — 1.7 KiB — 15 ms — h3https://www.gov.uk/assets/frontend/homepage/find-a-job-4d38717b0451da3bb223ddea7f681d79e48c1c022da5a08f16aba3f681503150.pngwww.gov.uk/assets/frontend/homepage... https://www.gov.uk/assets/frontend/homepage/find-a-job-4d38717b0451da3bb223ddea7f681d79e48c1c022da5a08f16aba3f681503150.png — 200 — 1.7 KiB — 17 ms — h3https://www.gov.uk/assets/frontend/app-promo/govuk-app-icon-0bca94cf05737106d8e80f32a66f773d7b6ff9b9652fc555917d855914309af0.pngwww.gov.uk/assets/frontend/app-prom... https://www.gov.uk/assets/frontend/app-promo/govuk-app-icon-0bca94cf05737106d8e80f32a66f773d7b6ff9b9652fc555917d855914309af0.png — 200 — 4.6 KiB — 17 ms — h3https://www.gov.uk/assets/frontend/favicon-d962d21b5bb443f546c097ea21b567cde639adef7370da45be5e349ba8d62d33.svgwww.gov.uk/assets/frontend/favicon-... https://www.gov.uk/assets/frontend/favicon-d962d21b5bb443f546c097ea21b567cde639adef7370da45be5e349ba8d62d33.svg — 200 — 1.2 KiB — 2 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 54ms · 13KB · £1/mo
www.gov.uk
Other
Optional
Execution 54ms
Transfer 13 KB
Monthly Cost £1/mo

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

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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