Skip to content
https://service.gov.uk

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
93
GRADE
A
FIX
2
REVIEW
1
PASS
12
INFO
2

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

Mobile Desktop
93
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.

2.55 s

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

2.60 s

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

24 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.

2.55 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.

2.61 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
12 PASS 1 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 (188.2 KiB of 188.4 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.

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

Green Hosting

No green hosting detected

A+
Page Weight Budget
188 KB transferred, 15 requests
PASS
188 KB transferred, 15 requests
Info::
Page weighs 746 KB (188 KB transferred)
Info::
15 HTTP requests
Info::
Estimated 0.04 g CO2 per page load
188 KB / 2.4 MB budget
188 KB transferred
15 requests
0.04 g CO2 per page load
Fonts 64.1 KiB 34%
JavaScript 54.9 KiB 29%
CSS 38.6 KiB 21%
Images 16.2 KiB 9%
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
Image Optimization
3 images, 0 KB saveable
PASS
3 images, 0 KB saveable
Info::
All images are well-optimized
3 images 16 KB
0 oversized -0 KB
3 legacy format
0 missing dimensions CLS risk
A+
JS Execution Cost
487ms total JS execution
PASS
487ms total JS execution
Info::
https://www.gov.uk/: 193ms CPU time
Info::
Unattributable: 153ms CPU time
Info::
https://www.gov.uk/assets/frontend/application-527...: 141ms CPU time
Warning::
Third-party scripts: 487ms (100% of total)

Main Thread Breakdown

Other 37% Script Evaluation 27% Style & Layout 24% Parse HTML & CSS 6% Rendering 5%
ScriptTotalScriptingParse/CompileParty
https://www.gov.uk/193ms8ms1ms3rd
Unattributable153ms8ms0ms3rd
https://www.gov.uk/assets/frontend/application-527c564759ff9aa7cb6e6b9fd78dc91ee7add2454050e3a6c441e53d9db254ba.js141ms122ms1ms3rd
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 1.5 s 2.0 s 2.5 s FCP 2.6 s LCP 2.6 shttps://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 — 4 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 — 4 ms — font-display: swap
bold-b542beb274-v2-35bf... woff2 swap
Size 31 KB
Load time 4 ms
Start 142 ms
Risk FOUT — text flashes from fallback to web font
light-94a07e06a1-v2-015... woff2 swap
Size 33 KB
Load time 4 ms
Start 142 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
15 resources · 188 KB · 26 KB savings available
PASS
15 resources · 188 KB · 26 KB savings available
Info::
Within 1MB page-weight target
Got: 188 KB
Warning::
14 third-party resources (100% of weight)
15 resources · 188.4 KiB · 14 third-party Within 1MB page-weight target
Font 34% · 64.1 KiB
JavaScript 29% · 54.9 KiB
CSS 21% · 38.6 KiB
Image 9% · 17.4 KiB
Document 7% · 13.3 KiB
Other 0% · 136 B

~25.9 KiB of savings available

Remove unused JavaScript: 25.9 KiB
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
15 requests over 165ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s 2.5 s FCP 2.6 s LCP 2.6 shttps://service.gov.uk// https://service.gov.uk/ — 302 — 136 B — 9 ms — h2https://www.gov.uk/www.gov.uk/ https://www.gov.uk/ — 200 — 13.3 KiB — 30 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 — 4 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 — 6 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 — 6 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 — 428 B — 9 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 — 12.1 KiB — 10 ms — h2https://www.gov.uk/assets/frontend/application-6e85cd8055c5001deff4f2121849990c359f2e9ce33f89c8e7e6bca2afaf323c.csswww.gov.uk/assets/frontend/applicat... https://www.gov.uk/assets/frontend/application-6e85cd8055c5001deff4f2121849990c359f2e9ce33f89c8e7e6bca2afaf323c.css — 200 — 37.0 KiB — 11 ms — h2https://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 — 517 B — 2 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 — 4 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 — 4 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 — 2 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 487ms · 55KB · £5/mo
www.gov.uk
Other
Optional
Execution 193ms
Transfer 13 KB
Monthly Cost £2/mo
Unattributable
Other
Optional
Execution 153ms
Transfer 0 KB
Monthly Cost £2/mo
www.gov.uk
Other
Optional
Execution 141ms
Transfer 41 KB
Unused 63%
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

63% of www.gov.uk'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.

Send Feedback