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

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.

1.08 s

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

1.33 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.

0.369

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

1.46 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.

1.33 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

8 PASS 3 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 (955.3 KiB of 955.7 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

14 images, 0 KB saveable

REVIEW

14 images, 0 KB saveable

All images are well-optimized

14 images 261 KB

0 oversized -0 KB

6 legacy format

0 missing dimensions CLS risk

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	3 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

956 KB transferred, 48 requests

PASS

956 KB transferred, 48 requests

Page weighs 1.7 MB (956 KB transferred)

48 HTTP requests

Estimated 0.20 g CO2 per page load

956 KB transferred

48 requests

0.20 g CO2 per page load

Images 261.0 KiB 27%

JavaScript 244.7 KiB 26%

HTML 166.8 KiB 17%

Fonts 142.7 KiB 15%

Other 73.9 KiB 8%

CSS 63.0 KiB 7%

Other 3.0 KiB 0%

Other 658 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+

JS Execution Cost

317ms total JS execution

PASS

317ms total JS execution

https://www.surrey.ac.uk/: 137ms CPU time

Unattributable: 95ms CPU time

https://www.googletagmanager.com/gtm.js?id=GTM-PQ5...: 85ms CPU time

Third-party scripts: 317ms (100% of total)

Main Thread Breakdown

Other 39% Script Evaluation 27% Style & Layout 18% Script Parsing & Compilation 7% Parse HTML & CSS 5% Rendering 3%

Script	Total	Scripting	Parse/Compile	Party
https://www.surrey.ac.uk/	137ms	9ms	0ms	3rd
Unattributable	95ms	8ms	0ms	3rd
https://www.googletagmanager.com/gtm.js?id=GTM-PQ53KG	85ms	64ms	18ms	3rd

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 380 ms

Start 807 ms

Risk FOUT — text flashes from fallback to web font

ProximaNova-Light.woff2 woff2 swap

Size 34 KB

Load time 364 ms

Start 807 ms

Risk FOUT — text flashes from fallback to web font

ProximaNova-Regular.woff2 woff2 swap

Size 34 KB

Load time 364 ms

Start 808 ms

Risk FOUT — text flashes from fallback to web font

ProximaNova-Semibold.woff2 woff2 swap

Size 34 KB

Load time 364 ms

Start 808 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

Page Weight Inventory

48 resources · 956 KB · 105 KB savings available

PASS

48 resources · 956 KB · 105 KB savings available

Within 1MB page-weight target

Got: 956 KB

~105 KB of savings available

47 third-party resources (100% of weight)

48 resources · 955.7 KiB · 47 third-party Within 1MB page-weight target

Image 28% · 263.6 KiB

JavaScript 26% · 244.7 KiB

Document 17% · 167.2 KiB

Font 15% · 142.7 KiB

Other 8% · 74.5 KiB

CSS 7% · 63.0 KiB

~105.4 KiB of savings available

Remove unused JavaScript: 105.4 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

48 resources			955.7 KiB

Network Waterfall

48 requests over 2291ms

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 317ms · 345KB · £3/mo

Script	Category	Execution	Transfer	Unused	Monthly Cost	Verdict
www.surrey.ac.uk www.surrey.ac.uk	Other	137ms	167 KB	—	£1/mo	Optional
Unattributable Unattributable	Other	95ms	0 KB	—	£1/mo	Optional
Google Tag Manager www.googletagmanager.com	Tag Manager	85ms	179 KB	48%	£1/mo	Optional

www.surrey.ac.uk

Other

Optional

Execution 137ms

Transfer 167 KB

Monthly Cost £1/mo

Unattributable

Other

Optional

Execution 95ms

Transfer 0 KB

Monthly Cost £1/mo

Google Tag Manager

Tag Manager

Optional

Execution 85ms

Transfer 179 KB

Unused 48%

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.