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https://www.gov.uk

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
95
GRADE
A
FIX
0
REVIEW
2
PASS
10
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.

404 ms

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

418 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.

404 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.

420 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
14
10 PASS 2 REVIEW
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
194 KB transferred, 17 requests
PASS
194 KB transferred, 17 requests
Info::
Page weighs 741 KB (194 KB transferred)
Info::
17 HTTP requests
Info::
Estimated 0.04 g CO2 per page load
194 KB / 2.4 MB budget
194 KB transferred
17 requests
0.04 g CO2 per page load
Fonts 64.1 KiB 33%
JavaScript 54.9 KiB 28%
CSS 36.1 KiB 19%
Images 24.2 KiB 12%
HTML 13.2 KiB 7%
Other 1.2 KiB 1%
0 2.4 MB 4.9 MB
Under budget
A+
Third-Party Impact
No third-party resources
PASS
No third-party resources
Info::
No third-party resources detected
No third-party resources detected — all resources are first-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+
JS Execution Cost
127ms total JS execution
PASS
127ms total JS execution
Info::
https://www.gov.uk/: 76ms CPU time
Info::
Unattributable: 51ms CPU time
Info::
Third-party scripts: 51ms (40% of total)

Main Thread Breakdown

Other 37% Style & Layout 31% Script Evaluation 21% Parse HTML & CSS 6% Rendering 5%
ScriptTotalScriptingParse/CompileParty
https://www.gov.uk/76ms3ms0ms1st
Unattributable51ms3ms0ms3rd
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 404 ms LCP 418 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 — 0 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 — 0 ms — font-display: swap
bold-b542beb274-v2-35bf... woff2 swap
Size 31 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
light-94a07e06a1-v2-015... woff2 swap
Size 33 KB
Load time 0 ms
Start 0 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%)✓1st
https://www.gov.uk/assets/frontend/govuk_publishing_components/vendor/lux/lux-measurer-d66192b1b665d415e1874e49a48138b7ae339548aa6cdb8687c7f9933e72b969.js1 KB—✓1st
https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-custom-data-b9e1806d1da2fa8ef1855d01aa71ba5eb0afc010dd2c4de3672cc7c7a39b0c8c.js0 KB—✓1st
https://www.gov.uk/assets/frontend/govuk_publishing_components/rum-loader-a65b10e18ceeba3bd8a2eac507c7f2c513cdc82f35097df903fdea87f1dc2e33.js0 KB—✓1st
https://www.gov.uk/assets/frontend/govuk_publishing_components/load-analytics-c0b21edf0d79bd3dd6172b0c5be4dfd3c073a8aab9275e31253be3a26762c9a9.js12 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

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+
HTTP Caching
max-age=300 (5 minutes)
PASS
max-age=300 (5 minutes)
Info::
Cache-Control header is set
Got: max-age=300, public
Info::
Effective TTL: 5 minutes (max-age=300)
Info::
ETag present — enables conditional (304) responses
Cache-Control

max-age=300, public

DirectiveValueMeaning
max-age300Cache for 5 minutes
public—Any cache may store this response
Effective TTL: 300 seconds
Network Waterfall
17 requests over 0ms
INFO

Performance analysis not available for this result.

Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
40% of JavaScript execution is third-party
First-party Third-party 51ms · 0KB · £1/mo
Unattributable
Other
Optional
Execution 51ms
Transfer 0 KB
Monthly Cost £1/mo

40% of JavaScript execution time comes from third-party scripts.

Why this matters

Third-party scripts (analytics, ads, social, A/B testing) often dominate execution time — every one is a perf-and-privacy tax.

Learn more ▾

Each third-party script is a black box: you don't control when it loads, what it executes, or how much it grows. They often account for a major share of total blocking time on average sites (HTTP Archive's Web Almanac documents the trend). Audit which ones you actually need, defer the rest, and use facade patterns (lite-youtube, lite-vimeo) for embedded media.

Source: web.dev / HTTP Archive Web Almanac

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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