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

Accessibility

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.

10.18 s

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

40.76 s

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

2.40 s

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

0.000

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

12.22 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.

41.46 s

Page Load Progression

664 ms

1.3 s

2.0 s

2.7 s

3.3 s

4.0 s

4.6 s

5.3 s

Checks

9 PASS 2 REVIEW 4 FIX

Page Weight Budget

Action

19.0 MB transferred, 156 requests

FIX

19.0 MB transferred, 156 requests

Page weighs 27.4 MB (19.0 MB transferred)

Images are 3.2 MB — compress or use modern formats

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

Got: 3.2 MB

JavaScript is 3.0 MB — consider code splitting or lazy loading

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Got: 3.0 MB

CSS is 384 KB — consider purging unused styles

Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.

Got: 384 KB

156 HTTP requests — consider bundling or reducing

Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.

Estimated 4.0 g CO2 per page load

19.0 MB transferred

156 requests

4.0 g CO2 per page load

Other 11.9 MiB 63%

Images 3.2 MiB 17%

JavaScript 3.0 MiB 16%

CSS 384.5 KiB 2%

Other 294.6 KiB 2%

Fonts 106.7 KiB 1%

HTML 79.5 KiB 0%

Other 62.1 KiB 0%

Other 1.9 KiB 0%

Other 841 B 0%

Other 0 B 0%

0 2.4 MB 4.9 MB

Over budget

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

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Why this matters

JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.

Source: web.dev

Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.

Why this matters

CSS bundle is large — purge unused styles (PurgeCSS, Tailwind JIT) to reduce CSS payload.

Source: web.dev

Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.

Why this matters

High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.

Source: web.dev

JS Execution Cost

Action

7250ms total JS execution

FIX

7250ms total JS execution

Unattributable: 1109ms CPU time

https://dur.ac.uk/: 761ms CPU time

https://www.googletagmanager.com/gtm.js?id=GTM-MD8...: 539ms CPU time

https://www.googletagmanager.com/gtag/js?id=G-HTQ6...: 463ms CPU time

https://dur.ac.uk/media/durham-university/site-ass...: 452ms CPU time

Third-party scripts: 5792ms (80% of total)

Main Thread Breakdown

Script Evaluation 56% Other 22% Script Parsing & Compilation 10% Style & Layout 7% Parse HTML & CSS 3%

Script	Total	Scripting	Parse/Compile	Party
Unattributable	1109ms	37ms	0ms	3rd
https://dur.ac.uk/	761ms	13ms	4ms	1st
https://www.googletagmanager.com/gtm.js?id=GTM-MD895GR	539ms	425ms	94ms	3rd
https://www.googletagmanager.com/gtag/js?id=G-HTQ6N1C1EK&cx=c&gtm=4e64k0	463ms	343ms	44ms	3rd
https://dur.ac.uk/media/durham-university/site-assets/js/dependencies-20231018.js	452ms	116ms	31ms	1st
https://www.googletagmanager.com/gtag/js?id=DC-14248141&cx=c&gtm=4e64k0	327ms	269ms	58ms	3rd
https://www.googletagmanager.com/gtag/js?id=AW-943473154&cx=c&gtm=4e64k0	307ms	268ms	37ms	3rd
https://www.googletagmanager.com/gtag/js?id=DC-13730620&cx=c&gtm=4e64k0	254ms	188ms	65ms	3rd
https://cdn.curator.io/5.0/curator.embed.js	238ms	130ms	42ms	3rd
https://code.jquery.com/jquery-3.5.1.min.js	233ms	196ms	21ms	3rd

Showing top 10 of 29 scripts

JS Bundles

Action

42 scripts, 908 KB unused

FIX

42 scripts, 908 KB unused

https://www.googletagmanager.com/gtag/js?id=G-HTQ6...: 70 KB unused (40%)

Consider code splitting or tree shaking to reduce unused code.

https://cdn.curator.io/5.0/curator.embed.js: 64 KB unused (63%)

Consider code splitting or tree shaking to reduce unused code.

https://www.googletagmanager.com/gtag/js?id=AW-465...: 63 KB unused (44%)

Consider code splitting or tree shaking to reduce unused code.

https://www.googletagmanager.com/gtag/js?id=AW-174...: 62 KB unused (43%)

Consider code splitting or tree shaking to reduce unused code.

https://www.googletagmanager.com/gtag/js?id=AW-943...: 62 KB unused (43%)

Consider code splitting or tree shaking to reduce unused code.

Total unused JavaScript: 908 KB

908 KB unused JavaScript

Downloaded but never executed on this page.

Script	Size	Unused	Minified	Party
https://www.googletagmanager.com/gtag/js?id=G-HTQ6N1C1EK&cx=c&gtm=4e64k0	173 KB	70 KB (40%)	✓	3rd
https://cdn.curator.io/5.0/curator.embed.js	103 KB	64 KB (63%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=AW-465216367&cx=c&gtm=4e64k0	144 KB	63 KB (44%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=AW-17497736984&cx=c&gtm=4e64k0	144 KB	62 KB (43%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=AW-943473154&cx=c&gtm=4e64k0	143 KB	62 KB (43%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=AW-958583275&cx=c&gtm=4e64k0	144 KB	62 KB (43%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=DC-4768938&cx=c&gtm=4e64k0	129 KB	61 KB (47%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=DC-4743369&cx=c&gtm=4e64k0	129 KB	61 KB (47%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=DC-14248141&cx=c&gtm=4e64k0	129 KB	61 KB (47%)	✓	3rd
https://www.googletagmanager.com/gtag/js?id=DC-13730620&cx=c&gtm=4e64k0	132 KB	61 KB (46%)	✓	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

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

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

Page Weight Inventory

Action

156 resources · 19.0 MB · 908 KB savings available

FIX

156 resources · 19.0 MB · 908 KB savings available

Page weight 18.0 MB over 1MB target

Got: 19.0 MB Expected: ≤ 1 MB

~908 KB of savings available

135 third-party resources (25% of weight)

5 resources over 200KB

156 resources · 19.0 MiB · 135 third-party 18.0 MiB over 1MB target

Media 63% · 11.9 MiB

Image 18% · 3.5 MiB

JavaScript 16% · 3.0 MiB

CSS 2% · 384.5 KiB

Font 1% · 106.7 KiB

Document 0% · 79.5 KiB

Other 0% · 64.8 KiB

~908.4 KiB of savings available

Remove unused JavaScript: 908.4 KiB

#	Resource	Type	Size	Cache	Unused	3rd party	Issues

156 resources			19.0 MiB

Image Optimization

63 images, 0 KB saveable

REVIEW

63 images, 0 KB saveable

All images are well-optimized

63 images 3.2 MB

0 oversized -0 KB

22 legacy format

0 missing dimensions CLS risk

Green Hosting

Action

Whether the site is served from green-energy infrastructure

REVIEW

Green Hosting

No green hosting detected

Third-Party Impact

25% third-party, 0 ms blocking

PASS

25% third-party, 0 ms blocking

Third-party code accounts for 25% of page weight (4.7 MiB of 19.0 MiB)

Third-party blocking time is low (0 ms)

75%

25%

First-party Third-party

A+

Text Compression

All text resources are compressed

PASS

All text resources are compressed

All text resources are properly compressed.

A+

Font Loading

6 fonts (107 KB)

PASS

6 fonts (107 KB)

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

Web fonts

107 KB total

Render-blocking

of 6

Dominant font-display

swap

Most common across fonts

Font loading timeline

Transfer FOIT (block) FOUT (swap)

KFO7CnqEu92Fr1ME7kSn66a... woff2 swap

Size 34 KB

Load time 114 ms

Start 670 ms

Risk FOUT — text flashes from fallback to web font

open-sans-v17-latin-reg... woff2 swap

Size 14 KB

Load time 153 ms

Start 706 ms

Risk FOUT — text flashes from fallback to web font

open-sans-v17-latin-600... woff2 swap

Size 15 KB

Load time 146 ms

Start 706 ms

Risk FOUT — text flashes from fallback to web font

open-sans-v17-latin-700... woff2 swap

Size 15 KB

Load time 149 ms

Start 706 ms

Risk FOUT — text flashes from fallback to web font

open-sans-v17-latin-300... woff2 swap

Size 15 KB

Load time 150 ms

Start 707 ms

Risk FOUT — text flashes from fallback to web font

open-sans-v17-latin-ita... woff2 swap

Size 14 KB

Load time 43 ms

Start 2.1 s

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

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

HTTP Caching

max-age=172800 (2 days)

PASS

max-age=172800 (2 days)

Cache-Control header is set

Got: max-age=172800

Effective TTL: 2 days (max-age=172800)

No ETag or Last-Modified header

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

Cache-Control

max-age=172800

Directive	Value	Meaning
max-age	172800	Cache for 2 days

Effective TTL: 172800 seconds

Network Waterfall

156 requests over 4020ms

INFO

HTML JavaScript CSS Images Fonts XHR/Fetch Other

Third-Party Script Cost

Per-script blocking time, transfer cost, and cache headers

INFO

80% of JavaScript execution is third-party

First-party Third-party 5792ms · 2128KB · £60/mo

Script	Category	Execution	Transfer	Unused	Monthly Cost	Verdict
Unattributable Unattributable	Other	1109ms	0 KB	—	£12/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	539ms	190 KB	23%	£6/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	463ms	173 KB	40%	£5/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	327ms	129 KB	47%	£3/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	307ms	143 KB	43%	£3/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	254ms	132 KB	46%	£3/mo	Costly
cdn.curator.io cdn.curator.io	Other	238ms	103 KB	63%	£2/mo	Costly
code.jquery.com code.jquery.com	Other	233ms	31 KB	—	£2/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	230ms	144 KB	43%	£2/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	221ms	144 KB	43%	£2/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	205ms	144 KB	44%	£2/mo	Costly
Microsoft Clarity scripts.clarity.ms	Session Replay	203ms	25 KB	—	£2/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	202ms	129 KB	45%	£2/mo	Costly
Google Tag Manager www.googletagmanager.com	Tag Manager	155ms	129 KB	47%	£2/mo	Optional
Facebook Pixel connect.facebook.net	Advertising	155ms	45 KB	—	£2/mo	Optional
Google Tag Manager www.googletagmanager.com	Tag Manager	151ms	129 KB	47%	£2/mo	Optional
Hotjar script.hotjar.com	Session Replay	134ms	57 KB	67%	£1/mo	Optional
hit.uptrendsdata.com hit.uptrendsdata.com	Other	125ms	37 KB	—	£1/mo	Optional
Facebook Pixel connect.facebook.net	Advertising	116ms	97 KB	36%	£1/mo	Optional
Facebook Pixel connect.facebook.net	Advertising	116ms	78 KB	69%	£1/mo	Optional
LinkedIn Insight snap.licdn.com	Advertising	77ms	19 KB	—	£1/mo	Optional
Google Analytics www.google-analytics.com	Analytics	63ms	21 KB	—	£1/mo	Optional
cdn.curator.io cdn.curator.io	Other	59ms	1 KB	—	£1/mo	Optional
Twitter/X Pixel static.ads-twitter.com	Advertising	57ms	13 KB	—	£1/mo	Optional
Facebook Pixel connect.facebook.net	Advertising	51ms	16 KB	—	£1/mo	Optional

Unattributable

Other

Costly

Execution 1109ms

Transfer 0 KB

Monthly Cost £12/mo

Google Tag Manager

Tag Manager

Costly

Execution 539ms

Transfer 190 KB

Unused 23%

Monthly Cost £6/mo

Google Tag Manager

Tag Manager

Costly

Execution 463ms

Transfer 173 KB

Unused 40%

Monthly Cost £5/mo

Google Tag Manager

Tag Manager

Costly

Execution 327ms

Transfer 129 KB

Unused 47%

Monthly Cost £3/mo

Google Tag Manager

Tag Manager

Costly

Execution 307ms

Transfer 143 KB

Unused 43%

Monthly Cost £3/mo

Google Tag Manager

Tag Manager

Costly

Execution 254ms

Transfer 132 KB

Unused 46%

Monthly Cost £3/mo

cdn.curator.io

Other

Costly

Execution 238ms

Transfer 103 KB

Unused 63%

Monthly Cost £2/mo

code.jquery.com

Other

Costly

Execution 233ms

Transfer 31 KB

Monthly Cost £2/mo

Google Tag Manager

Tag Manager

Costly

Execution 230ms

Transfer 144 KB

Unused 43%

Monthly Cost £2/mo

Google Tag Manager

Tag Manager

Costly

Execution 221ms

Transfer 144 KB

Unused 43%

Monthly Cost £2/mo

Google Tag Manager

Tag Manager

Costly

Execution 205ms

Transfer 144 KB

Unused 44%

Monthly Cost £2/mo

Microsoft Clarity

Session Replay

Costly

Execution 203ms

Transfer 25 KB

Monthly Cost £2/mo

Google Tag Manager

Tag Manager

Costly

Execution 202ms

Transfer 129 KB

Unused 45%

Monthly Cost £2/mo

Google Tag Manager

Tag Manager

Optional

Execution 155ms

Transfer 129 KB

Unused 47%

Monthly Cost £2/mo

Facebook Pixel

Advertising

Optional

Execution 155ms

Transfer 45 KB

Monthly Cost £2/mo

Google Tag Manager

Tag Manager

Optional

Execution 151ms

Transfer 129 KB

Unused 47%

Monthly Cost £2/mo

Hotjar

Session Replay

Optional

Execution 134ms

Transfer 57 KB

Unused 67%

Monthly Cost £1/mo

hit.uptrendsdata.com

Other

Optional

Execution 125ms

Transfer 37 KB

Monthly Cost £1/mo

Facebook Pixel

Advertising

Optional

Execution 116ms

Transfer 97 KB

Unused 36%

Monthly Cost £1/mo

Facebook Pixel

Advertising

Optional

Execution 116ms

Transfer 78 KB

Unused 69%

Monthly Cost £1/mo

LinkedIn Insight

Advertising

Optional

Execution 77ms

Transfer 19 KB

Monthly Cost £1/mo

Google Analytics

Analytics

Optional

Execution 63ms

Transfer 21 KB

Monthly Cost £1/mo

cdn.curator.io

Other

Optional

Execution 59ms

Transfer 1 KB

Monthly Cost £1/mo

Twitter/X Pixel

Advertising

Optional

Execution 57ms

Transfer 13 KB

Monthly Cost £1/mo

Facebook Pixel

Advertising

Optional

Execution 51ms

Transfer 16 KB

Monthly Cost £1/mo

These scripts may cost more than they're worth

Unattributable adds 1109ms and costs ~£12/month
Google Tag Manager adds 539ms and costs ~£6/month
Google Tag Manager adds 463ms and costs ~£5/month
Google Tag Manager adds 327ms and costs ~£3/month
Google Tag Manager adds 307ms and costs ~£3/month
Google Tag Manager adds 254ms and costs ~£3/month
cdn.curator.io adds 238ms and costs ~£2/month
code.jquery.com adds 233ms and costs ~£2/month
Google Tag Manager adds 230ms and costs ~£2/month
Google Tag Manager adds 221ms and costs ~£2/month
Google Tag Manager adds 205ms and costs ~£2/month
Microsoft Clarity adds 203ms and costs ~£2/month
Google Tag Manager adds 202ms and costs ~£2/month

80% 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

Unattributable takes 1109ms 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 539ms 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 463ms 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 327ms 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 307ms 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 254ms 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

cdn.curator.io takes 238ms 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

63% of cdn.curator.io'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

code.jquery.com takes 233ms 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 230ms 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 221ms 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 205ms 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

Microsoft Clarity takes 203ms 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 202ms 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

67% of Hotjar'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

69% of Facebook Pixel'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.