Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.

SCORE

GRADE

FIX

REVIEW

PASS

INFO

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

Mobile Desktop

Performance

Accessibility

100

Best Practices

SEO

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

1.39 s

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

2.50 s

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

9 ms

Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.

0.029

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

1.39 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.

2.50 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

7 PASS 4 REVIEW 2 FIX

Third-Party Impact

Action

100% third-party, 0 ms blocking

FIX

100% third-party, 0 ms blocking

Third-party code accounts for 100% of page weight (1.7 MiB of 1.7 MiB)

Third-party blocking time is low (0 ms)

100%

First-party Third-party

Page Weight Inventory

Action

26 resources · 1.7 MB · 57 KB savings available

FIX

26 resources · 1.7 MB · 57 KB savings available

Page weight 761 KB over 1MB target

Got: 1.7 MB Expected: ≤ 1 MB

~57 KB of savings available

25 third-party resources (100% of weight)

1 resources over 200KB

26 resources · 1.7 MiB · 25 third-party 761.3 KiB over 1MB target

Image 79% · 1.4 MiB

JavaScript 13% · 240.3 KiB

Font 4% · 64.0 KiB

CSS 3% · 46.3 KiB

Document 1% · 22.5 KiB

Other 0% · 1.7 KiB

~57.4 KiB of savings available

Remove unused JavaScript: 57.4 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

26 resources			1.7 MiB

Page Weight Budget

Action

1.7 MB transferred, 26 requests

REVIEW

1.7 MB transferred, 26 requests

Page weighs 2.6 MB (1.7 MB transferred)

Images are 1.4 MB — compress or use modern formats

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Got: 1.4 MB

26 HTTP requests

Estimated 0.37 g CO2 per page load

1.7 MB transferred

26 requests

0.37 g CO2 per page load

Images 1.4 MiB 79%

JavaScript 240.3 KiB 13%

Fonts 64.0 KiB 4%

CSS 46.3 KiB 3%

HTML 22.0 KiB 1%

Other 1.8 KiB 0%

Other 1.1 KiB 0%

Other 616 B 0%

0 2.4 MB 4.9 MB

Approaching limit

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Why this matters

Image bandwidth is high — modern formats (WebP/AVIF) and resizing typically cut it 50%+.

Source: web.dev

Image Optimization

3 images, 0 KB saveable

REVIEW

3 images, 0 KB saveable

https://healthmedia.blog.gov.uk/wp-content/uploads... is missing width/height — may cause layout shift

Set explicit width and height to prevent CLS.

https://educationhub.blog.gov.uk/wp-content/upload... is missing width/height — may cause layout shift

Set explicit width and height to prevent CLS.

3 images 1.4 MB

0 oversized -0 KB

3 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

JS Bundles

11 scripts, 57 KB unused

REVIEW

11 scripts, 57 KB unused

https://cc.cdn.civiccomputing.com/9/cookieControl-...: 57 KB unused (47%)

Consider code splitting or tree shaking to reduce unused code.

Total unused JavaScript: 57 KB

57 KB unused JavaScript

Downloaded but never executed on this page.

Script	Size	Unused	Minified	Party
https://cc.cdn.civiccomputing.com/9/cookieControl-9.x.min.js?ver=6.9.4	123 KB	57 KB (47%)	✓	3rd
https://www.blog.gov.uk/wp-includes/js/jquery/jquery.min.js?ver=3.7.1	30 KB	—	✓	3rd
https://www.blog.gov.uk/wp-includes/js/jquery/jquery-migrate.min.js?ver=3.4.1	5 KB	—	✓	3rd
https://www.blog.gov.uk/wp-content/themes/gds-blogs/build/main-1a574665cb89c6954a0fc51bba2076ee798236b6.min.js?ver=6.9.4	5 KB	—	✓	3rd
https://www.blog.gov.uk/wp-content/plugins/gds-cookies-and-analytics/assets/cookieControlConfig.js?ver=6.9.4	2 KB	—	✓	3rd
https://www.blog.gov.uk/wp-content/plugins/dxw-digest/assets/js/dxw-digest.js?ver=6.9.4	1 KB	—	✓	3rd
https://www.blog.gov.uk/wp-content/themes/gds-blogs-root/build/main.min.js?ver=6.9.4	11 KB	—	✓	3rd
https://www.blog.gov.uk/wp-content/themes/gds-blogs/build/govuk-frontend-load.js?ver=6.9.4	0 KB	—	✓	3rd
https://www.blog.gov.uk/wp-content/plugins/aurora-heatmap/js/aurora-heatmap.min.js?ver=1.7.1	39 KB	—	✓	3rd
https://www.blog.gov.uk/wp-content/plugins/page-links-to/dist/new-tab.js?ver=3.4.1	13 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

Green Hosting

Action

Whether the site is served from green-energy infrastructure

REVIEW

Green Hosting

No green hosting detected

A+

Text Compression

All text resources are compressed

PASS

All text resources are compressed

All text resources are properly compressed.

A+

JS Execution Cost

212ms total JS execution

PASS

212ms total JS execution

https://www.blog.gov.uk/: 80ms CPU time

https://cc.cdn.civiccomputing.com/9/cookieControl-...: 76ms CPU time

Unattributable: 57ms CPU time

Third-party scripts: 212ms (100% of total)

Main Thread Breakdown

Script Evaluation 41% Other 25% Style & Layout 20% Script Parsing & Compilation 6% Parse HTML & CSS 5%

Script	Total	Scripting	Parse/Compile	Party
https://www.blog.gov.uk/	80ms	1ms	1ms	3rd
https://cc.cdn.civiccomputing.com/9/cookieControl-9.x.min.js?ver=6.9.4	76ms	61ms	10ms	3rd
Unattributable	57ms	1ms	0ms	3rd

A+

Font Loading

2 fonts (64 KB)

PASS

2 fonts (64 KB)

2 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

64 KB total

Render-blocking

of 2

Dominant font-display

swap

Most common across fonts

Font loading timeline

Transfer FOIT (block) FOUT (swap)

bold-b542beb274-v2.woff2 woff2 swap

Size 31 KB

Load time 26 ms

Start 610 ms

Risk FOUT — text flashes from fallback to web font

light-94a07e06a1-v2.woff2 woff2 swap

Size 33 KB

Load time 25 ms

Start 611 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+

Resource Caching

All resources properly cached

PASS

All resources properly cached

No caching issues found

All static resources have appropriate caching headers.

A+

Critical Rendering Path

No render-blocking resources

PASS

No render-blocking resources

No render-blocking resources detected

A+

Resource Hints

No optimization needed

PASS

No optimization needed

No resource hint issues

HTTP Caching

max-age=3600 (1 hour)

PASS

max-age=3600 (1 hour)

Cache-Control header is set

Got: max-age=3600

Effective TTL: 1 hour (max-age=3600)

No ETag or Last-Modified header

Conditional requests (304 Not Modified) are not possible without validators.

Cache-Control

max-age=3600

Directive	Value	Meaning
max-age	3600	Cache for 1 hour

Effective TTL: 3600 seconds

Network Waterfall

26 requests over 701ms

INFO

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 212ms · 145KB · £2/mo

Script	Category	Execution	Transfer	Unused	Monthly Cost	Verdict
www.blog.gov.uk www.blog.gov.uk	Other	80ms	22 KB	—	£1/mo	Optional
cc.cdn.civiccomputing.com cc.cdn.civiccomputing.com	Other	76ms	123 KB	47%	£1/mo	Optional
Unattributable Unattributable	Other	57ms	0 KB	—	£1/mo	Optional

www.blog.gov.uk

Other

Optional

Execution 80ms

Transfer 22 KB

Monthly Cost £1/mo

cc.cdn.civiccomputing.com

Other

Optional

Execution 76ms

Transfer 123 KB

Unused 47%

Monthly Cost £1/mo

Unattributable

Other

Optional

Execution 57ms

Transfer 0 KB

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

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.