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https://nationalarchives.gov.uk

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
91
GRADE
A
FIX
2
REVIEW
1
PASS
10
INFO
2

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

Mobile Desktop
86
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.

1.05 s

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

1.11 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.

0.205

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

1.05 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.

1.11 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
15
10 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 (535.0 KiB of 535.2 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
535 KB transferred, 23 requests
PASS
535 KB transferred, 23 requests
Info::
Page weighs 781 KB (535 KB transferred)
Info::
Fonts are 223 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 223 KB
Info::
23 HTTP requests
Info::
Estimated 0.11 g CO2 per page load
535 KB / 2.4 MB budget
535 KB transferred
23 requests
0.11 g CO2 per page load
Fonts 222.9 KiB 42%
Images 216.2 KiB 40%
CSS 53.3 KiB 10%
JavaScript 19.8 KiB 4%
HTML 13.5 KiB 3%
Other 9.5 KiB 2%
0 2.4 MB 4.9 MB
Under budget

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

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
6 images, 0 KB saveable
PASS
6 images, 0 KB saveable
Info::
All images are well-optimized
6 images 216 KB
0 oversized -0 KB
0 legacy format
0 missing dimensions CLS risk
A+
JS Execution Cost
371ms total JS execution
PASS
371ms total JS execution
Warning::
https://www.nationalarchives.gov.uk/: 308ms CPU time
Info::
Unattributable: 63ms CPU time
Warning::
Third-party scripts: 371ms (100% of total)

Main Thread Breakdown

Other 34% Style & Layout 31% Rendering 26% Script Evaluation 5%
ScriptTotalScriptingParse/CompileParty
https://www.nationalarchives.gov.uk/308ms3ms0ms3rd
Unattributable63ms3ms0ms3rd
A+
Font Loading
4 fonts (223 KB)
PASS
4 fonts (223 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

223 KB total

Render-blocking

0

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 500 ms 1.0 s FCP 1.0 s LCP 1.1 shttps://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2memvYaGs126MiZpBA-UvWbX... https://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2 — 42.0 KiB — 30 ms — font-display: swaphttps://use.typekit.net/af/a025b5/00000000000000007735a262/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3l https://use.typekit.net/af/a025b5/00000000000000007735a262/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 34.8 KiB — 10 ms — font-display: swaphttps://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2L0x5DF4xlVMF-BfR8bXMIjh... https://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2 — 32.0 KiB — 29 ms — font-display: swaphttps://www.nationalarchives.gov.uk/static/assets/fonts/fa-solid-900.woff2fa-solid-900.woff2 https://www.nationalarchives.gov.uk/static/assets/fonts/fa-solid-900.woff2 — 114.1 KiB — 38 ms — font-display: swap
memvYaGs126MiZpBA-UvWbX... woff2 swap
Size 42 KB
Load time 30 ms
Start 248 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 35 KB
Load time 10 ms
Start 248 ms
Risk FOUT — text flashes from fallback to web font
L0x5DF4xlVMF-BfR8bXMIjh... woff2 swap
Size 32 KB
Load time 29 ms
Start 249 ms
Risk FOUT — text flashes from fallback to web font
fa-solid-900.woff2 woff2 swap
Size 114 KB
Load time 38 ms
Start 249 ms
Risk FOUT — text flashes from fallback to web font
  • 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 ~57 KB and ~114 ms

A+
JS Bundles
2 scripts, 0 KB unused
PASS
2 scripts, 0 KB unused
0 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.nationalarchives.gov.uk/static/main.min.js?v=26.04.16.163012 KB—✓3rd
https://www.nationalarchives.gov.uk/static/analytics.min.js?v=26.04.16.16308 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
23 resources · 535 KB · 0 KB savings available
PASS
23 resources · 535 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 535 KB
Warning::
22 third-party resources (100% of weight)
23 resources · 535.2 KiB · 22 third-party Within 1MB page-weight target
Image 42% · 225.4 KiB
Font 42% · 222.9 KiB
CSS 10% · 53.3 KiB
JavaScript 4% · 19.8 KiB
Document 3% · 13.5 KiB
Other 0% · 255 B
Network Waterfall
23 requests over 336ms
INFO
0 ms 500 ms 1.0 s FCP 1.0 s LCP 1.1 shttps://nationalarchives.gov.uk// https://nationalarchives.gov.uk/ — 302 — 255 B — 44 ms — h2https://www.nationalarchives.gov.uk/www.nationalarchives.gov.uk/ https://www.nationalarchives.gov.uk/ — 200 — 13.5 KiB — 32 ms — http/1.1https://www.nationalarchives.gov.uk/static/main.css?v=26.04.16.1630www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/main.css?v=26.04.16.1630 — 200 — 20.0 KiB — 13 ms — http/1.1https://use.typekit.net/kaq6qqh.cssuse.typekit.net/kaq6qqh.css https://use.typekit.net/kaq6qqh.css — 200 — 854 B — 44 ms — h2https://fonts.googleapis.com/css2?family=Open+Sans:wght@400..700&family=Roboto+Mono:wght@400..500&display=swapfonts.googleapis.com/css2?family=Op... https://fonts.googleapis.com/css2?family=Open+Sans:wght@400..700&family=Roboto+Mono:wght@400..500&display=swap — 200 — 2.1 KiB — 73 ms — h2https://www.nationalarchives.gov.uk/static/font-awesome.css?v=26.04.16.1630www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/font-awesome.css?v=26.04.16.1630 — 200 — 22.0 KiB — 42 ms — http/1.1https://www.nationalarchives.gov.uk/static/homepage.css?v=26.04.16.1630www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/homepage.css?v=26.04.16.1630 — 200 — 2.2 KiB — 35 ms — http/1.1https://www.nationalarchives.gov.uk/static/main.min.js?v=26.04.16.1630www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/main.min.js?v=26.04.16.1630 — 200 — 12.2 KiB — 38 ms — http/1.1https://www.nationalarchives.gov.uk/static/analytics.min.js?v=26.04.16.1630www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/analytics.min.js?v=26.04.16.1630 — 200 — 7.6 KiB — 38 ms — http/1.1https://www.nationalarchives.gov.uk/static/print.css?v=26.04.16.1630www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/print.css?v=26.04.16.1630 — 200 — 2.9 KiB — 35 ms — http/1.1https://www.nationalarchives.gov.uk/static/ie.css?v=26.04.16.1630www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/ie.css?v=26.04.16.1630 — 200 — 3.0 KiB — 35 ms — http/1.1https://p.typekit.net/p.css?s=1&k=kaq6qqh&ht=tk&f=17141&a=157040217&app=typekit&e=cssp.typekit.net/p.css?s=1&k=kaq6qqh&h... https://p.typekit.net/p.css?s=1&k=kaq6qqh&ht=tk&f=17141&a=157040217&app=typekit&e=css — 200 — 173 B — 20 ms — h2https://www.nationalarchives.gov.uk/media/images/Emmeline-pankhurst-.23b1d58d.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webpwww.nationalarchives.gov.uk/media/i... https://www.nationalarchives.gov.uk/media/images/Emmeline-pankhurst-.23b1d58d.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webp — 200 — 14.0 KiB — 32 ms — http/1.1https://www.nationalarchives.gov.uk/media/images/On_the_Record_VE_Day.90141c71.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webpwww.nationalarchives.gov.uk/media/i... https://www.nationalarchives.gov.uk/media/images/On_the_Record_VE_Day.90141c71.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webp — 200 — 26.0 KiB — 32 ms — http/1.1https://www.nationalarchives.gov.uk/media/images/Collection_image_E3_iKGMwH6.2e16d0ba.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webpwww.nationalarchives.gov.uk/media/i... https://www.nationalarchives.gov.uk/media/images/Collection_image_E3_iKGMwH6.2e16d0ba.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webp — 200 — 59.2 KiB — 32 ms — http/1.1https://www.nationalarchives.gov.uk/media/images/The_National_Archiv_GNi1HG1.2e16d0ba.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webpwww.nationalarchives.gov.uk/media/i... https://www.nationalarchives.gov.uk/media/images/The_National_Archiv_GNi1HG1.2e16d0ba.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webp — 200 — 37.0 KiB — 33 ms — http/1.1https://www.nationalarchives.gov.uk/media/images/hg-us-declaration-indepe.6b5ea91c.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webpwww.nationalarchives.gov.uk/media/i... https://www.nationalarchives.gov.uk/media/images/hg-us-declaration-indepe.6b5ea91c.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webp — 200 — 52.6 KiB — 32 ms — http/1.1https://www.nationalarchives.gov.uk/media/images/researching-in-docu_cmfInz2.6f6e9d24.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webpwww.nationalarchives.gov.uk/media/i... https://www.nationalarchives.gov.uk/media/images/researching-in-docu_cmfInz2.6f6e9d24.fill-600x400.format-webp.webpquality-70.bgcolor-fff.webp — 200 — 27.3 KiB — 31 ms — http/1.1https://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2fonts.gstatic.com/s/opensans/v44/me... https://fonts.gstatic.com/s/opensans/v44/memvYaGs126MiZpBA-UvWbX2vVnXBbObj2OVTS-mu0SC55I.woff2 — 200 — 42.0 KiB — 30 ms — h3https://use.typekit.net/af/a025b5/00000000000000007735a262/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3use.typekit.net/af/a025b5/000000000... https://use.typekit.net/af/a025b5/00000000000000007735a262/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 200 — 34.8 KiB — 10 ms — h2https://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2fonts.gstatic.com/s/robotomono/v31/... https://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2 — 200 — 32.0 KiB — 29 ms — h3https://www.nationalarchives.gov.uk/static/assets/fonts/fa-solid-900.woff2www.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/assets/fonts/fa-solid-900.woff2 — 200 — 114.1 KiB — 38 ms — http/1.1https://www.nationalarchives.gov.uk/static/assets/images/favicon.icowww.nationalarchives.gov.uk/static/... https://www.nationalarchives.gov.uk/static/assets/images/favicon.ico — 200 — 9.3 KiB — 8 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 371ms · 13KB · £4/mo
www.nationalarchives.gov.uk
Other
Costly
Execution 308ms
Transfer 13 KB
Monthly Cost £3/mo
Unattributable
Other
Optional
Execution 63ms
Transfer 0 KB
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • www.nationalarchives.gov.uk adds 308ms 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.nationalarchives.gov.uk takes 308ms 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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