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https://legislation.gov.uk

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
90
GRADE
A
FIX
2
REVIEW
3
PASS
10
INFO
2

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

Mobile Desktop
68
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
98
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.
92
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.

4.54 s

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

5.71 s

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.

0.031

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

4.54 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.

5.72 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 3 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 (444.4 KiB of 444.5 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
Image Optimization
Action
11 images, 0 KB saveable
REVIEW
11 images, 0 KB saveable
Warning::
https://www.legislation.gov.uk/images/chrome/site_... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.legislation.gov.uk/images/analytics/co... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
11 images 280 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

B
JS Execution Cost
678ms total JS execution
REVIEW
678ms total JS execution
Warning::
https://www.legislation.gov.uk/scripts/jquery-3.7....: 277ms CPU time
Info::
Unattributable: 207ms CPU time
Info::
https://www.legislation.gov.uk/: 194ms CPU time
Warning::
Third-party scripts: 678ms (100% of total)

Main Thread Breakdown

Other 50% Style & Layout 21% Script Evaluation 18% Rendering 4%
ScriptTotalScriptingParse/CompileParty
https://www.legislation.gov.uk/scripts/jquery-3.7.1.min.js277ms112ms9ms3rd
Unattributable207ms6ms0ms3rd
https://www.legislation.gov.uk/194ms11ms2ms3rd
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
444 KB transferred, 30 requests
PASS
444 KB transferred, 30 requests
Info::
Page weighs 864 KB (444 KB transferred)
Info::
30 HTTP requests
Info::
Estimated 0.09 g CO2 per page load
444 KB / 2.4 MB budget
444 KB transferred
30 requests
0.09 g CO2 per page load
Images 279.5 KiB 63%
JavaScript 62.9 KiB 14%
CSS 57.1 KiB 13%
Fonts 36.7 KiB 8%
HTML 6.1 KiB 1%
Other 2.1 KiB 0%
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+
Font Loading
1 fonts (37 KB)
PASS
1 fonts (37 KB)
Info::
1 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

1

37 KB total

Render-blocking

0

of 1

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 FCP 4.5 s LCP 5.7 shttps://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 36.7 KiB — 35 ms — font-display: swap
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 37 KB
Load time 35 ms
Start 1.0 s
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
8 scripts, 0 KB unused
PASS
8 scripts, 0 KB unused
Warning::
https://www.legislation.gov.uk/scripts/chrome.js: unminified — 9 KB could be saved
0 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.legislation.gov.uk/scripts/jquery-3.7.1.min.js30 KB—✓3rd
https://www.legislation.gov.uk/scripts/CentralConfig.js4 KB—✓3rd
https://www.legislation.gov.uk/scripts/survey/survey.js2 KB—✓3rd
https://www.legislation.gov.uk/scripts/chrome.js17 KB—✗3rd
https://www.legislation.gov.uk/scripts/homepageChrome.js2 KB—✓3rd
https://www.legislation.gov.uk/scripts/jquery-cookie-directive/jquery.cookie.js2 KB—✓3rd
https://www.legislation.gov.uk/scripts/jquery-cookie-directive/jquery-cookie-functions.js2 KB—✓3rd
https://www.legislation.gov.uk/scripts/cookie-directive.js4 KB—✓3rd
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
30 resources · 444 KB · 0 KB savings available
PASS
30 resources · 444 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 444 KB
Warning::
29 third-party resources (100% of weight)
Info::
1 resources over 200KB
30 resources · 444.5 KiB · 29 third-party Within 1MB page-weight target
Image 63% · 281.5 KiB
JavaScript 14% · 62.9 KiB
CSS 13% · 57.1 KiB
Font 8% · 36.7 KiB
Document 1% · 6.2 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
30 requests over 1181ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s FCP 4.5 s LCP 5.7 shttps://legislation.gov.uk// https://legislation.gov.uk/ — 301 — 90 B — 84 ms — h2https://www.legislation.gov.uk/www.legislation.gov.uk/ https://www.legislation.gov.uk/ — 200 — 5.7 KiB — 449 ms — http/1.1https://www.legislation.gov.uk/styles/screen.csswww.legislation.gov.uk/styles/scree... https://www.legislation.gov.uk/styles/screen.css — 200 — 20.5 KiB — 23 ms — http/1.1https://www.legislation.gov.uk/styles/survey/survey.csswww.legislation.gov.uk/styles/surve... https://www.legislation.gov.uk/styles/survey/survey.css — 200 — 1.2 KiB — 21 ms — http/1.1https://www.legislation.gov.uk/scripts/jquery-3.7.1.min.jswww.legislation.gov.uk/scripts/jque... https://www.legislation.gov.uk/scripts/jquery-3.7.1.min.js — 200 — 30.3 KiB — 23 ms — http/1.1https://www.legislation.gov.uk/scripts/CentralConfig.jswww.legislation.gov.uk/scripts/Cent... https://www.legislation.gov.uk/scripts/CentralConfig.js — 200 — 4.2 KiB — 21 ms — http/1.1https://www.legislation.gov.uk/scripts/survey/survey.jswww.legislation.gov.uk/scripts/surv... https://www.legislation.gov.uk/scripts/survey/survey.js — 200 — 1.8 KiB — 21 ms — http/1.1https://www.legislation.gov.uk/scripts/chrome.jswww.legislation.gov.uk/scripts/chro... https://www.legislation.gov.uk/scripts/chrome.js — 200 — 16.7 KiB — 23 ms — http/1.1https://www.legislation.gov.uk/scripts/homepageChrome.jswww.legislation.gov.uk/scripts/home... https://www.legislation.gov.uk/scripts/homepageChrome.js — 200 — 2.1 KiB — 21 ms — http/1.1https://www.legislation.gov.uk/styles/website.csswww.legislation.gov.uk/styles/websi... https://www.legislation.gov.uk/styles/website.css — 200 — 30.0 KiB — 24 ms — http/1.1https://fonts.googleapis.com/css2?family=Roboto:ital,wght@0,100;0,200;0,300;0,400;0,500;0,700;0,900;1,100;1,300;1,400;1,500;1,700;1,900&display=swapfonts.googleapis.com/css2?family=Ro... https://fonts.googleapis.com/css2?family=Roboto:ital,wght@0,100;0,200;0,300;0,400;0,500;0,700;0,900;1,100;1,300;1,400;1,500;1,700;1,900&display=swap — 200 — 3.0 KiB — 97 ms — h2https://www.legislation.gov.uk/styles/print.csswww.legislation.gov.uk/styles/print... https://www.legislation.gov.uk/styles/print.css — 200 — 1.1 KiB — 22 ms — http/1.1https://www.legislation.gov.uk/styles/buy-now.csswww.legislation.gov.uk/styles/buy-n... https://www.legislation.gov.uk/styles/buy-now.css — 200 — 1.4 KiB — 43 ms — http/1.1https://www.legislation.gov.uk/scripts/jquery-cookie-directive/jquery.cookie.jswww.legislation.gov.uk/scripts/jque... https://www.legislation.gov.uk/scripts/jquery-cookie-directive/jquery.cookie.js — 200 — 1.7 KiB — 21 ms — http/1.1https://www.legislation.gov.uk/scripts/jquery-cookie-directive/jquery-cookie-functions.jswww.legislation.gov.uk/scripts/jque... https://www.legislation.gov.uk/scripts/jquery-cookie-directive/jquery-cookie-functions.js — 200 — 1.8 KiB — 21 ms — http/1.1https://www.legislation.gov.uk/scripts/cookie-directive.jswww.legislation.gov.uk/scripts/cook... https://www.legislation.gov.uk/scripts/cookie-directive.js — 200 — 4.3 KiB — 20 ms — http/1.1https://www.legislation.gov.uk/images/chrome/site_logo_legislation.gifwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/site_logo_legislation.gif — 200 — 7.3 KiB — 23 ms — http/1.1https://www.legislation.gov.uk/images/chrome/ogl-symbol.gifwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/ogl-symbol.gif — 200 — 1.6 KiB — 22 ms — http/1.1https://www.legislation.gov.uk/images/chrome/homepageCountryBG/welcome.pngwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/homepageCountryBG/welcome.png — 200 — 18.8 KiB — 29 ms — http/1.1https://www.legislation.gov.uk/images/chrome/nat-archive-delivered-en.svgwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/nat-archive-delivered-en.svg — 200 — 5.2 KiB — 28 ms — http/1.1https://www.legislation.gov.uk/images/uk-govt-crest.pngwww.legislation.gov.uk/images/uk-go... https://www.legislation.gov.uk/images/uk-govt-crest.png — 200 — 232.6 KiB — 92 ms — http/1.1https://www.legislation.gov.uk/images/ogl.pngwww.legislation.gov.uk/images/ogl.p... https://www.legislation.gov.uk/images/ogl.png — 200 — 9.0 KiB — 65 ms — http/1.1https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2fonts.gstatic.com/s/roboto/v51/KFO7... https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 200 — 36.7 KiB — 35 ms — h3https://www.legislation.gov.uk/images/analytics/cookiesBannerIgnored.gifwww.legislation.gov.uk/images/analy... https://www.legislation.gov.uk/images/analytics/cookiesBannerIgnored.gif — 200 — 638 B — 44 ms — http/1.1https://www.legislation.gov.uk/images/chrome/pause-circle-outline.svgwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/pause-circle-outline.svg — 200 — 1.2 KiB — 44 ms — http/1.1https://www.legislation.gov.uk/images/chrome/checkmark-sharp.svgwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/checkmark-sharp.svg — 200 — 881 B — 40 ms — http/1.1https://www.legislation.gov.uk/images/chrome/close-sharp-inverse.svgwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/close-sharp-inverse.svg — 200 — 923 B — 40 ms — http/1.1https://www.googletagmanager.com/ns.html?id=GTM-TWB7339www.googletagmanager.com/ns.html?id... https://www.googletagmanager.com/ns.html?id=GTM-TWB7339 — 200 — 437 B — 101 ms — h2https://www.legislation.gov.uk/images/chrome/settings-sharp.svgwww.legislation.gov.uk/images/chrom... https://www.legislation.gov.uk/images/chrome/settings-sharp.svg — 200 — 1.6 KiB — 21 ms — http/1.1https://www.legislation.gov.uk/favicon.icowww.legislation.gov.uk/favicon.ico https://www.legislation.gov.uk/favicon.ico — 200 — 2.0 KiB — 21 ms — http/1.1
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 678ms · 36KB · £7/mo
www.legislation.gov.uk
Other
Costly
Execution 277ms
Transfer 30 KB
Monthly Cost £3/mo
Unattributable
Other
Costly
Execution 207ms
Transfer 0 KB
Monthly Cost £2/mo
www.legislation.gov.uk
Other
Optional
Execution 194ms
Transfer 6 KB
Monthly Cost £2/mo

These scripts may cost more than they're worth

  • www.legislation.gov.uk adds 277ms and costs ~£3/month
  • Unattributable adds 207ms and costs ~£2/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.legislation.gov.uk takes 277ms 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 207ms 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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