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

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
91
GRADE
A
FIX
2
REVIEW
2
PASS
11
INFO
2

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

Mobile Desktop
74
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.

4.24 s

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

4.47 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.

0.001

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

4.24 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.

4.49 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
11 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 (418.0 KiB of 418.3 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
JS Execution Cost
Action
1313ms total JS execution
REVIEW
1313ms total JS execution
Warning::
https://www.nationalarchives.gov.uk/: 1062ms CPU time
Info::
Unattributable: 182ms CPU time
Info::
https://www.nationalarchives.gov.uk/static/main.mi...: 69ms CPU time
Warning::
Third-party scripts: 1313ms (100% of total)

Main Thread Breakdown

Other 35% Rendering 30% Style & Layout 25% Parse HTML & CSS 4% Script Evaluation 4%
ScriptTotalScriptingParse/CompileParty
https://www.nationalarchives.gov.uk/1062ms6ms1ms3rd
Unattributable182ms6ms0ms3rd
https://www.nationalarchives.gov.uk/static/main.min.js?v=26.04.16.163069ms17ms6ms3rd
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
418 KB transferred, 20 requests
PASS
418 KB transferred, 20 requests
Info::
Page weighs 665 KB (418 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::
20 HTTP requests
Info::
Estimated 0.09 g CO2 per page load
418 KB / 2.4 MB budget
418 KB transferred
20 requests
0.09 g CO2 per page load
Fonts 222.9 KiB 53%
Images 99.2 KiB 24%
CSS 53.3 KiB 13%
JavaScript 19.8 KiB 5%
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
3 images, 0 KB saveable
PASS
3 images, 0 KB saveable
Info::
All images are well-optimized
3 images 99 KB
0 oversized -0 KB
0 legacy format
0 missing dimensions CLS risk
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 1.0 s 2.0 s 3.0 s 4.0 s FCP 4.2 s LCP 4.5 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 — 19 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 — 14 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 — 16 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 — 19 ms — font-display: swap
memvYaGs126MiZpBA-UvWbX... woff2 swap
Size 42 KB
Load time 19 ms
Start 583 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 35 KB
Load time 14 ms
Start 583 ms
Risk FOUT — text flashes from fallback to web font
L0x5DF4xlVMF-BfR8bXMIjh... woff2 swap
Size 32 KB
Load time 16 ms
Start 584 ms
Risk FOUT — text flashes from fallback to web font
fa-solid-900.woff2 woff2 swap
Size 114 KB
Load time 19 ms
Start 584 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
3 hints, 0 missing preconnects
PASS
3 hints, 0 missing preconnects
Info::
Page uses 3 resource hint(s)

Current Resource Hints

preconnect
3
preload
—
dns-prefetch
—
prefetch
—

3 resource hints configured

A
Page Weight Inventory
20 resources · 418 KB · 0 KB savings available
PASS
20 resources · 418 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 418 KB
Warning::
19 third-party resources (100% of weight)
20 resources · 418.3 KiB · 19 third-party Within 1MB page-weight target
Font 53% · 222.9 KiB
Image 26% · 108.5 KiB
CSS 13% · 53.3 KiB
JavaScript 5% · 19.8 KiB
Document 3% · 13.5 KiB
Other 0% · 254 B
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
20 requests over 640ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s FCP 4.2 s LCP 4.5 shttps://nationalarchives.gov.uk// https://nationalarchives.gov.uk/ — 302 — 254 B — 25 ms — h2https://www.nationalarchives.gov.uk/www.nationalarchives.gov.uk/ https://www.nationalarchives.gov.uk/ — 200 — 13.5 KiB — 383 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 — 23 ms — http/1.1https://use.typekit.net/kaq6qqh.cssuse.typekit.net/kaq6qqh.css https://use.typekit.net/kaq6qqh.css — 200 — 853 B — 43 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 — 63 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 — 33 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 — 27 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 — 30 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 — 30 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 — 26 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 — 10 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 — 24 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 — 22 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 — 21 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 — 21 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 — 19 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 — 14 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 — 16 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 — 19 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 — 6 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 1313ms · 26KB · £14/mo
www.nationalarchives.gov.uk
Other
Costly
Execution 1062ms
Transfer 13 KB
Monthly Cost £11/mo
Unattributable
Other
Optional
Execution 182ms
Transfer 0 KB
Monthly Cost £2/mo
www.nationalarchives.gov.uk
Other
Optional
Execution 69ms
Transfer 12 KB
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • www.nationalarchives.gov.uk adds 1062ms and costs ~£11/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 1062ms 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.

Send Feedback