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https://shef.ac.uk

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
79
GRADE
C
FIX
5
REVIEW
3
PASS
7
INFO
2

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

Mobile Desktop
55
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
99
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
96
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
92
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.

5.53 s

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

8.07 s

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

134 ms

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

0.067

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

9.26 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.

11.12 s

Page Load Progression

735 ms
1.5 s
2.2 s
2.9 s
3.7 s
4.4 s
5.1 s
5.9 s
Checks
17
7 PASS 3 REVIEW 5 FIX
D
Page Weight Budget
Action
2.1 MB transferred, 53 requests
FIX
2.1 MB transferred, 53 requests
Info::
Page weighs 3.5 MB (2.1 MB transferred)
Warning::
Images are 1.3 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 1.3 MB
Info::
Fonts are 365 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 365 KB
Info::
53 HTTP requests
Info::
Estimated 0.44 g CO2 per page load
2.1 MB / 2.4 MB budget
2.1 MB transferred
53 requests
0.44 g CO2 per page load
Images 1.3 MiB 62%
Fonts 365.5 KiB 17%
JavaScript 291.3 KiB 14%
CSS 60.8 KiB 3%
Other 47.8 KiB 2%
HTML 24.0 KiB 1%
Other 17.8 KiB 1%
Other 2.6 KiB 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

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

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 (2.1 MiB of 2.1 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
D
JS Execution Cost
Action
2133ms total JS execution
FIX
2133ms total JS execution
Warning::
https://sheffield.ac.uk/: 735ms CPU time
Warning::
https://sheffield.ac.uk/sites/default/files/js/js_...: 582ms CPU time
Warning::
Unattributable: 470ms CPU time
Warning::
https://cdn-ukwest.onetrust.com/scripttemplates/20...: 264ms CPU time
Info::
https://cdn-ukwest.onetrust.com/consent/a3110129-5...: 82ms CPU time
Warning::
Third-party scripts: 2133ms (100% of total)

Main Thread Breakdown

Script Evaluation 33% Other 24% Style & Layout 21% Rendering 8% Parse HTML & CSS 7% Script Parsing & Compilation 7%
ScriptTotalScriptingParse/CompileParty
https://sheffield.ac.uk/735ms8ms2ms3rd
https://sheffield.ac.uk/sites/default/files/js/js_2vteZ97-nwa3u581M7hObqBeT9L58uGfk8ciEUfAce8.js?scope=footer&delta=0&language=en&theme=uos_public&include=eJxNjEEKgDAMBD9U7JNCm0ap1q7G5KCvFxHE28wchhcp1aCUmKGlosePhlHRTXoJ8-6iJ3ml5AbGujUxiX8JjoM2z61ynBpyauFyzTTCe0n2jN98A0vELbc582ms376ms69ms3rd
Unattributable470ms68ms0ms3rd
https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/otBannerSdk.js264ms173ms63ms3rd
https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/OtAutoBlock.js82ms70ms10ms3rd
D
Page Weight Inventory
Action
53 resources · 2.1 MB · 140 KB savings available
FIX
53 resources · 2.1 MB · 140 KB savings available
Warning::
Page weight 1.1 MB over 1MB target
Got: 2.1 MB Expected: ≤ 1 MB
Info::
~140 KB of savings available
Warning::
52 third-party resources (100% of weight)
Info::
2 resources over 200KB
53 resources · 2.1 MiB · 52 third-party 1.1 MiB over 1MB target
Image 63% · 1.3 MiB
Font 17% · 365.5 KiB
JavaScript 15% · 320.1 KiB
CSS 3% · 65.4 KiB
Document 1% · 24.5 KiB
Other 1% · 16.4 KiB

~139.6 KiB of savings available

Remove unused JavaScript: 139.6 KiB
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.

B
Image Optimization
27 images, 0 KB saveable
REVIEW
27 images, 0 KB saveable
Warning::
https://sheffield.ac.uk/themes/custom/uos_public/i... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
27 images 1.3 MB
0 oversized -0 KB
26 legacy format
1 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

B
JS Bundles
7 scripts, 140 KB unused
REVIEW
7 scripts, 140 KB unused
Warning::
https://sheffield.ac.uk/sites/default/files/js/js_...: 74 KB unused (53%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://cdn-ukwest.onetrust.com/scripttemplates/20...: 66 KB unused (53%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 140 KB
140 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://sheffield.ac.uk/sites/default/files/js/js_2vteZ97-nwa3u581M7hObqBeT9L58uGfk8ciEUfAce8.js?scope=footer&delta=0&language=en&theme=uos_public&include=eJxNjEEKgDAMBD9U7JNCm0ap1q7G5KCvFxHE28wchhcp1aCUmKGlosePhlHRTXoJ8-6iJ3ml5AbGujUxiX8JjoM2z61ynBpyauFyzTTCe0n2jN98A0vELbc140 KB74 KB (53%)✓3rd
https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/otBannerSdk.js124 KB66 KB (53%)✓3rd
https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/OtAutoBlock.js17 KB—✓3rd
https://cdn-ukwest.onetrust.com/scripttemplates/otSDKStub.js9 KB—✓3rd
https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/a3110129-5f04-4e81-9c5e-b494a7836315.json2 KB—✓3rd
https://sheffield.ac.uk/sites/default/files/google_tag/primary/google_tag.script.js?tdwnjd1 KB—✓3rd
https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/6d67dddd-eaa6-4c34-b216-835e23374a00/en.json26 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

C
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
Info::
All text resources are compressed
All text resources are properly compressed.
A+
Font Loading
6 fonts (365 KB)
PASS
6 fonts (365 KB)
Info::
6 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

6

365 KB total

Render-blocking

0

of 6

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 5.0 s 6.0 s 7.0 s 8.0 s FCP 5.5 s LCP 8.1 shttps://sheffield.ac.uk/themes/custom/common/uos/fonts/source-sans-3-v15-latin-regular.woff2source-sans-3-v15-latin... https://sheffield.ac.uk/themes/custom/common/uos/fonts/source-sans-3-v15-latin-regular.woff2 — 16.1 KiB — 267 ms — font-display: swaphttps://sheffield.ac.uk/themes/custom/common/uos/fonts/source-serif-4-v8-latin-700.woff2source-serif-4-v8-latin... https://sheffield.ac.uk/themes/custom/common/uos/fonts/source-serif-4-v8-latin-700.woff2 — 22.1 KiB — 348 ms — font-display: swaphttps://sheffield.ac.uk/themes/custom/common/uos/fonts/source-sans-3-v15-latin-900.woff2source-sans-3-v15-latin... https://sheffield.ac.uk/themes/custom/common/uos/fonts/source-sans-3-v15-latin-900.woff2 — 15.2 KiB — 407 ms — font-display: swaphttps://sheffield.ac.uk/themes/custom/common/uos/fonts/HotMess.ttfHotMess.ttf https://sheffield.ac.uk/themes/custom/common/uos/fonts/HotMess.ttf — 215.2 KiB — 1.0 s — font-display: swaphttps://sheffield.ac.uk/themes/custom/common/uos/fonts/source-sans-3-v15-latin-700.woff2source-sans-3-v15-latin... https://sheffield.ac.uk/themes/custom/common/uos/fonts/source-sans-3-v15-latin-700.woff2 — 16.0 KiB — 522 ms — font-display: swaphttps://sheffield.ac.uk/themes/custom/common/uos/fonts/SourceSerif4Roman-Regular.woff2SourceSerif4Roman-Regul... https://sheffield.ac.uk/themes/custom/common/uos/fonts/SourceSerif4Roman-Regular.woff2 — 80.8 KiB — 819 ms — font-display: swap
source-sans-3-v15-latin... woff2 swap
Size 16 KB
Load time 267 ms
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
source-serif-4-v8-latin... woff2 swap
Size 22 KB
Load time 348 ms
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
source-sans-3-v15-latin... woff2 swap
Size 15 KB
Load time 407 ms
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
HotMess.ttf ttf swap
Size 215 KB
Load time 1.0 s
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
source-sans-3-v15-latin... woff2 swap
Size 16 KB
Load time 522 ms
Start 3.8 s
Risk FOUT — text flashes from fallback to web font
SourceSerif4Roman-Regul... woff2 swap
Size 81 KB
Load time 819 ms
Start 3.8 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)

Fixing the unchecked items could save ~172 KB and ~344 ms

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
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
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
53 requests over 5846ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s 6.0 s 7.0 s 8.0 s FCP 5.5 s LCP 8.1 shttps://shef.ac.uk// https://shef.ac.uk/ — 301 — 179 B — 1.1 s — http/1.1https://www.sheffield.ac.uk/www.sheffield.ac.uk/ https://www.sheffield.ac.uk/ — 301 — 310 B — 1.1 s — http/1.1https://sheffield.ac.uk/sheffield.ac.uk/ https://sheffield.ac.uk/ — 200 — 24.0 KiB — 946 ms — http/1.1https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/OtAutoBlock.jscdn-ukwest.onetrust.com/consent/a31... https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/OtAutoBlock.js — 200 — 16.8 KiB — 68 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/otSDKStub.jscdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/otSDKStub.js — 200 — 9.1 KiB — 39 ms — h2https://sheffield.ac.uk/sites/default/files/css/css_0B-QxziIjQfKmCZM4hNEb7gF6bID8sdb99Y5aJ4wlj0.css?delta=0&language=en&theme=uos_public&include=eJxNj2tuwzAMgy_kxkcSZFtptTmWq0eG7PRLg2HdH4H6SAlg_aTGLgpYq2hjGflPLavKcBot0XD2A2gr1HLF6aebPp5BekAwYLhU2WYnp_x_SR0PCYfGVmU_01kGVelpouJdcT4sN42JfXmTJcaM0tke1JKSTRnGO4Fj6QQrdyfNb367eLLDnLZc0CiFGFwvar53KdjTzvRl-ZrLJi3Og-_QAqvEaPiq85v8AQBhbFssheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/css/css_0B-QxziIjQfKmCZM4hNEb7gF6bID8sdb99Y5aJ4wlj0.css?delta=0&language=en&theme=uos_public&include=eJxNj2tuwzAMgy_kxkcSZFtptTmWq0eG7PRLg2HdH4H6SAlg_aTGLgpYq2hjGflPLavKcBot0XD2A2gr1HLF6aebPp5BekAwYLhU2WYnp_x_SR0PCYfGVmU_01kGVelpouJdcT4sN42JfXmTJcaM0tke1JKSTRnGO4Fj6QQrdyfNb367eLLDnLZc0CiFGFwvar53KdjTzvRl-ZrLJi3Og-_QAqvEaPiq85v8AQBhbFs — 200 — 5.2 KiB — 318 ms — http/1.1https://sheffield.ac.uk/sites/default/files/css/css_aLjOu322Fb88fUU5m2nCEukbdfZLOpfebsSyCTJHqy0.css?delta=1&language=en&theme=uos_public&include=eJxNj2tuwzAMgy_kxkcSZFtptTmWq0eG7PRLg2HdH4H6SAlg_aTGLgpYq2hjGflPLavKcBot0XD2A2gr1HLF6aebPp5BekAwYLhU2WYnp_x_SR0PCYfGVmU_01kGVelpouJdcT4sN42JfXmTJcaM0tke1JKSTRnGO4Fj6QQrdyfNb367eLLDnLZc0CiFGFwvar53KdjTzvRl-ZrLJi3Og-_QAqvEaPiq85v8AQBhbFssheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/css/css_aLjOu322Fb88fUU5m2nCEukbdfZLOpfebsSyCTJHqy0.css?delta=1&language=en&theme=uos_public&include=eJxNj2tuwzAMgy_kxkcSZFtptTmWq0eG7PRLg2HdH4H6SAlg_aTGLgpYq2hjGflPLavKcBot0XD2A2gr1HLF6aebPp5BekAwYLhU2WYnp_x_SR0PCYfGVmU_01kGVelpouJdcT4sN42JfXmTJcaM0tke1JKSTRnGO4Fj6QQrdyfNb367eLLDnLZc0CiFGFwvar53KdjTzvRl-ZrLJi3Og-_QAqvEaPiq85v8AQBhbFs — 200 — 55.6 KiB — 692 ms — http/1.1https://sheffield.ac.uk/themes/custom/uos_public/images/logos/uos-crest.svgsheffield.ac.uk/themes/custom/uos_p... https://sheffield.ac.uk/themes/custom/uos_public/images/logos/uos-crest.svg — 200 — 7.1 KiB — 760 ms — http/1.1https://sheffield.ac.uk/sites/default/files/styles/main_home/public/2026-03/Cover_v03_large%20%281%29.jpg?h=76294784&itok=rFrH5kntsheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/styles/main_home/public/2026-03/Cover_v03_large%20%281%29.jpg?h=76294784&itok=rFrH5knt — 200 — 207.2 KiB — 1.4 s — http/1.1https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/a3110129-5f04-4e81-9c5e-b494a7836315.jsoncdn-ukwest.onetrust.com/consent/a31... https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/a3110129-5f04-4e81-9c5e-b494a7836315.json — 200 — 2.4 KiB — 49 ms — h2https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2026-03/Cover_v03_large%20%281%29.jpg?h=647c1a54&itok=5FnZ3f3Osheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2026-03/Cover_v03_large%20%281%29.jpg?h=647c1a54&itok=5FnZ3f3O — 200 — 57.1 KiB — 1.0 s — http/1.1https://sheffield.ac.uk/sites/default/files/google_tag/primary/google_tag.script.js?tdwnjdsheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/google_tag/primary/google_tag.script.js?tdwnjd — 200 — 1.1 KiB — 742 ms — http/1.1https://geolocation.onetrust.com/cookieconsentpub/v1/geo/locationgeolocation.onetrust.com/cookiecons... https://geolocation.onetrust.com/cookieconsentpub/v1/geo/location — 200 — 207 B — 22 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/otBannerSdk.jscdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/otBannerSdk.js — 200 — 124.1 KiB — 19 ms — h2https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/6d67dddd-eaa6-4c34-b216-835e23374a00/en.jsoncdn-ukwest.onetrust.com/consent/a31... https://cdn-ukwest.onetrust.com/consent/a3110129-5f04-4e81-9c5e-b494a7836315/6d67dddd-eaa6-4c34-b216-835e23374a00/en.json — 200 — 26.5 KiB — 35 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/assets/otFloatingFlat.jsoncdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/assets/otFloatingFlat.json — 200 — 3.0 KiB — 19 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/assets/v2/otPcCenter.jsoncdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/assets/v2/otPcCenter.json — 200 — 13.2 KiB — 24 ms — h2https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/assets/otCommonStyles.csscdn-ukwest.onetrust.com/scripttempl... https://cdn-ukwest.onetrust.com/scripttemplates/202510.2.0/assets/otCommonStyles.css — 200 — 4.6 KiB — 16 ms — h2https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2019-02/economics_undergrads.jpg?h=7eb62d8e&itok=3N1RKbzZsheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2019-02/economics_undergrads.jpg?h=7eb62d8e&itok=3N1RKbzZ — 200 — 41.0 KiB — 718 ms — http/1.1https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2020-03/pgde-30564.jpg?h=82e026d0&itok=LtF34PvCsheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2020-03/pgde-30564.jpg?h=82e026d0&itok=LtF34PvC — 200 — 52.9 KiB — 251 ms — http/1.1data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="32" height="24…www.w3.org/2000/svg" version="1.1" ... data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="32" height="24… — 200 — 0 B — 0 ms — 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https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2025-05/image.jpg?h=1ca0f118&itok=mUVDVM36 — 200 — 58.6 KiB — 220 ms — http/1.1https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2019-04/light-blur-city-scape_0.jpg?h=b5941091&itok=Kkgagqessheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2019-04/light-blur-city-scape_0.jpg?h=b5941091&itok=Kkgagqes — 200 — 66.5 KiB — 233 ms — http/1.1https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2019-10/SheffieldCityView_0.jpg?h=b7adc06c&itok=2m5inwuQsheffield.ac.uk/sites/default/files... https://sheffield.ac.uk/sites/default/files/styles/mobile_single_column_2x/public/2019-10/SheffieldCityView_0.jpg?h=b7adc06c&itok=2m5inwuQ — 200 — 81.0 KiB — 271 ms — http/1.1https://sheffield.ac.uk/themes/custom/uos_public/images/accDOWN.pngsheffield.ac.uk/themes/custom/uos_p... https://sheffield.ac.uk/themes/custom/uos_public/images/accDOWN.png — 200 — 1.4 KiB — 192 ms — http/1.1https://sheffield.ac.uk/themes/custom/uos_public/favicon.svgsheffield.ac.uk/themes/custom/uos_p... https://sheffield.ac.uk/themes/custom/uos_public/favicon.svg — 200 — 4.8 KiB — 194 ms — http/1.1https://sheffield.ac.uk/themes/custom/uos_public/favicon.icosheffield.ac.uk/themes/custom/uos_p... https://sheffield.ac.uk/themes/custom/uos_public/favicon.ico — 200 — 12.6 KiB — 220 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 2133ms · 305KB · £22/mo
sheffield.ac.uk
Other
Costly
Execution 735ms
Transfer 24 KB
Monthly Cost £8/mo
sheffield.ac.uk
Other
Costly
Execution 582ms
Transfer 140 KB
Unused 53%
Monthly Cost £6/mo
Unattributable
Other
Costly
Execution 470ms
Transfer 0 KB
Monthly Cost £5/mo
cdn-ukwest.onetrust.com
Other
Costly
Execution 264ms
Transfer 124 KB
Unused 53%
Monthly Cost £3/mo
cdn-ukwest.onetrust.com
Other
Optional
Execution 82ms
Transfer 17 KB
Monthly Cost £1/mo

These scripts may cost more than they're worth

  • sheffield.ac.uk adds 735ms and costs ~£8/month
  • sheffield.ac.uk adds 582ms and costs ~£6/month
  • Unattributable adds 470ms and costs ~£5/month
  • cdn-ukwest.onetrust.com adds 264ms and costs ~£3/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

sheffield.ac.uk takes 735ms 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

sheffield.ac.uk takes 582ms 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

53% of sheffield.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

Unattributable takes 470ms 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-ukwest.onetrust.com takes 264ms 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

53% of cdn-ukwest.onetrust.com'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.

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