Performance

· 17 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

100

Accessibility

100

Best Practices

100

SEO

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

3.23 s

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

4.15 s

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

110 ms

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

0.448

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

3.59 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.

6.55 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

9 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 (779.1 KiB of 779.5 KiB)

Third-party blocking time is low (0 ms)

100%

First-party Third-party

HTTP Caching

Action

No cache headers

FIX

No cache headers

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.

Image Optimization

11 images, 0 KB saveable

REVIEW

11 images, 0 KB saveable

All images are well-optimized

11 images 85 KB

0 oversized -0 KB

7 legacy format

0 missing dimensions CLS risk

JS Execution Cost

Action

1639ms total JS execution

REVIEW

1639ms total JS execution

https://www.surrey.ac.uk/: 765ms CPU time

Unattributable: 379ms CPU time

https://www.googletagmanager.com/gtm.js?id=GTM-PQ5...: 353ms CPU time

https://www.surrey.ac.uk/themes/custom/surrey_2024...: 74ms CPU time

https://www.surrey.ac.uk/sites/default/files/js/js...: 69ms CPU time

Third-party scripts: 1639ms (100% of total)

Main Thread Breakdown

Style & Layout 31% Other 31% Script Evaluation 25% Script Parsing & Compilation 6% Parse HTML & CSS 4% Rendering 3%

Script	Total	Scripting	Parse/Compile	Party
https://www.surrey.ac.uk/	765ms	35ms	1ms	3rd
Unattributable	379ms	33ms	0ms	3rd
https://www.googletagmanager.com/gtm.js?id=GTM-PQ53KG	353ms	270ms	74ms	3rd
https://www.surrey.ac.uk/themes/custom/surrey_2024/dist/js/custom/cookie-consent.js?tdsuht	74ms	9ms	1ms	3rd
https://www.surrey.ac.uk/sites/default/files/js/js_5J6pLjqetCgxzofYaHlsl_D7ui4cQ0kOhkzNjdlE00E.js?scope=footer&delta=6&language=en&theme=surrey&include=eJxdjEEOwjAMBD-EVVTxH7Skq9aC2JGdVOrvOQCHcp0ZTY4IHtPmlQ0rpeORl_zACjUx7Lqiq9sX3-frfJuK-1MpxS1p_U-NSEoSUTb5nU9JY6QbXppcZEHH2XobTSptvAGJ9Trc	69ms	39ms	14ms	3rd

JS Bundles

11 scripts, 105 KB unused

REVIEW

11 scripts, 105 KB unused

https://www.googletagmanager.com/gtm.js?id=GTM-PQ5...: 85 KB unused (48%)

Consider code splitting or tree shaking to reduce unused code.

https://www.surrey.ac.uk/sites/default/files/js/js...: 21 KB unused (71%)

Consider code splitting or tree shaking to reduce unused code.

Total unused JavaScript: 105 KB

105 KB unused JavaScript

Downloaded but never executed on this page.

Script	Size	Unused	Minified	Party
https://www.googletagmanager.com/gtm.js?id=GTM-PQ53KG	179 KB	85 KB (48%)	✓	3rd
https://www.surrey.ac.uk/sites/default/files/js/js_5J6pLjqetCgxzofYaHlsl_D7ui4cQ0kOhkzNjdlE00E.js?scope=footer&delta=6&language=en&theme=surrey&include=eJxdjEEOwjAMBD-EVVTxH7Skq9aC2JGdVOrvOQCHcp0ZTY4IHtPmlQ0rpeORl_zACjUx7Lqiq9sX3-frfJuK-1MpxS1p_U-NSEoSUTb5nU9JY6QbXppcZEHH2XobTSptvAGJ9Trc	29 KB	21 KB (71%)	✓	3rd
https://www.surrey.ac.uk/sites/default/files/js/js_e1yp0WAqUMS7Pj1XbPb8uVQw6kzbevBRW2rDMisRw1g.js?scope=footer&delta=0&language=en&theme=surrey&include=eJxdjEEOwjAMBD-EVVTxH7Skq9aC2JGdVOrvOQCHcp0ZTY4IHtPmlQ0rpeORl_zACjUx7Lqiq9sX3-frfJuK-1MpxS1p_U-NSEoSUTb5nU9JY6QbXppcZEHH2XobTSptvAGJ9Trc	4 KB	—	✓	3rd
https://www.surrey.ac.uk/themes/custom/surrey/assets/dist/js/custom/navigation.js?tdsuht	2 KB	—	✓	3rd
https://www.surrey.ac.uk/sites/default/files/js/js_Uxb4wibJrcJ0OTsmxQiH5jHFcysgnQXTfYe7fVAqlms.js?scope=footer&delta=2&language=en&theme=surrey&include=eJxdjEEOwjAMBD-EVVTxH7Skq9aC2JGdVOrvOQCHcp0ZTY4IHtPmlQ0rpeORl_zACjUx7Lqiq9sX3-frfJuK-1MpxS1p_U-NSEoSUTb5nU9JY6QbXppcZEHH2XobTSptvAGJ9Trc	4 KB	—	✓	3rd
https://www.surrey.ac.uk/themes/custom/surrey_2024/dist/js/custom/helpers.js?tdsuht	1 KB	—	✓	3rd
https://www.surrey.ac.uk/themes/custom/surrey_2024/dist/js/custom/personalisation-state.js?tdsuht	2 KB	—	✓	3rd
https://www.surrey.ac.uk/themes/custom/surrey_2024/dist/js/custom/cookie-consent.js?tdsuht	2 KB	—	✓	3rd
https://www.surrey.ac.uk/themes/custom/surrey_2024/dist/js/custom/course-search-homepage.js?tdsuht	4 KB	—	✓	3rd
https://www.surrey.ac.uk/themes/custom/surrey_2024/dist/js/custom/personalised-data.js?tdsuht	15 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

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

Page Weight Budget

779 KB transferred, 45 requests

PASS

779 KB transferred, 45 requests

Page weighs 1.5 MB (779 KB transferred)

45 HTTP requests

Estimated 0.16 g CO2 per page load

779 KB transferred

45 requests

0.16 g CO2 per page load

JavaScript 244.8 KiB 31%

HTML 166.7 KiB 21%

Fonts 142.6 KiB 18%

Images 84.7 KiB 11%

Other 74.0 KiB 9%

CSS 63.0 KiB 8%

Other 3.0 KiB 0%

Other 681 B 0%

0 2.4 MB 4.9 MB

Under budget

A+

Text Compression

All text resources are compressed

PASS

All text resources are compressed

All text resources are properly compressed.

A+

Font Loading

4 fonts (143 KB)

PASS

4 fonts (143 KB)

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

Web fonts

143 KB total

Render-blocking

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline

Transfer FOIT (block) FOUT (swap)

352B6B_0_0.woff2 woff2 swap

Size 41 KB

Load time 374 ms

Start 867 ms

Risk FOUT — text flashes from fallback to web font

ProximaNova-Light.woff2 woff2 swap

Size 34 KB

Load time 372 ms

Start 868 ms

Risk FOUT — text flashes from fallback to web font

ProximaNova-Regular.woff2 woff2 swap

Size 34 KB

Load time 372 ms

Start 868 ms

Risk FOUT — text flashes from fallback to web font

ProximaNova-Semibold.woff2 woff2 swap

Size 34 KB

Load time 372 ms

Start 868 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

5 hints, 0 missing preconnects

PASS

5 hints, 0 missing preconnects

Page uses 5 resource hint(s)

Current Resource Hints

preconnect

—

preload

dns-prefetch

prefetch

—

5 resource hints configured

Page Weight Inventory

45 resources · 779 KB · 105 KB savings available

PASS

45 resources · 779 KB · 105 KB savings available

Within 1MB page-weight target

Got: 779 KB

~105 KB of savings available

44 third-party resources (100% of weight)

45 resources · 779.5 KiB · 44 third-party Within 1MB page-weight target

JavaScript 31% · 244.8 KiB

Document 21% · 167.1 KiB

Font 18% · 142.6 KiB

Image 11% · 87.2 KiB

Other 10% · 74.7 KiB

CSS 8% · 63.0 KiB

~105.4 KiB of savings available

Remove unused JavaScript: 105.4 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

45 resources			779.5 KiB

A+

Render-Blocking Resources

No render-blocking resources detected

PASS

No render-blocking resources detected

No render-blocking resources detected in <head>

A+

Third-Party Resources

No third-party resources detected

PASS

No third-party resources detected

Network Waterfall

45 requests over 2360ms

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 1639ms · 377KB · £17/mo

Script	Category	Execution	Transfer	Unused	Monthly Cost	Verdict
www.surrey.ac.uk www.surrey.ac.uk	Other	765ms	167 KB	—	£8/mo	Costly
Unattributable Unattributable	Other	379ms	0 KB	—	£4/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	353ms	179 KB	48%	£4/mo	Costly
www.surrey.ac.uk www.surrey.ac.uk	Other	74ms	2 KB	—	£1/mo	Optional
www.surrey.ac.uk www.surrey.ac.uk	Other	69ms	29 KB	71%	£1/mo	Optional

www.surrey.ac.uk

Other

Costly

Execution 765ms

Transfer 167 KB

Monthly Cost £8/mo

Unattributable

Other

Costly

Execution 379ms

Transfer 0 KB

Monthly Cost £4/mo

Google Tag Manager

Tag Manager

Costly

Execution 353ms

Transfer 179 KB

Unused 48%

Monthly Cost £4/mo

www.surrey.ac.uk

Other

Optional

Execution 74ms

Transfer 2 KB

Monthly Cost £1/mo

www.surrey.ac.uk

Other

Optional

Execution 69ms

Transfer 29 KB

Unused 71%

Monthly Cost £1/mo

These scripts may cost more than they're worth

www.surrey.ac.uk adds 765ms and costs ~£8/month
Unattributable adds 379ms and costs ~£4/month
Google Tag Manager adds 353ms and costs ~£4/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.surrey.ac.uk takes 765ms 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 379ms 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

Google Tag Manager takes 353ms 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

71% of www.surrey.ac.uk's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

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.