Performance
· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.Performance-focused optimization plan with CWV assessment, top offenders, and time estimates
First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.
908 ms
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
1.38 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
12 ms
Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.
0.001
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
908 ms
Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.
2.42 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 sDThird-Party ImpactAction100% third-party, 0 ms blockingFIX
DJS BundlesAction14 scripts, 367 KB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.googletagmanager.com/gtag/js?id=G-LME5ZDDFS0&cx=c>m=4e64h1h1 | 171 KB | 68 KB (40%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-NDH95W87 | 191 KB | 68 KB (35%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-11002703160&cx=c>m=4e64h1h1 | 146 KB | 65 KB (45%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-17946844669&cx=c>m=4e64h1h1 | 145 KB | 64 KB (44%) | ✓ | 3rd |
| https://cdn-ukwest.onetrust.com/scripttemplates/202511.1.0/otBannerSdk.js | 124 KB | 64 KB (52%) | ✓ | 3rd |
| https://www.imperial.ac.uk/assets/website/js/build/application.2.3.5.min.js | 52 KB | 37 KB (72%) | ✓ | 3rd |
| https://cdnjs.cloudflare.com/ajax/libs/gsap/3.10.4/gsap.min.js | 23 KB | — | ✓ | 3rd |
| https://www.imperial.ac.uk/assets/website/js/require/vendor/jquery3-migrate.js | 15 KB | — | ✗ | 3rd |
| https://browser.sentry-cdn.com/8.33.0/bundle.min.js | 24 KB | — | ✓ | 3rd |
| https://cdn-ukwest.onetrust.com/consent/6d9efb9d-b605-406f-b8b3-c9644859d064/OtAutoBlock.js | 3 KB | — | ✓ | 3rd |
Consider code splitting or tree shaking to reduce unused code.
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.
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.
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.
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.
This bundle has high unused code — code-split or tree-shake to ship only what executes.
Source: web.dev / Lighthouse coverage
DPage Weight InventoryAction44 resources · 2.0 MB · 367 KB savings availableFIX
~366.7 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 44 resources | 2.0 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
CPage Weight BudgetAction2.0 MB transferred, 44 requestsREVIEW
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.
Source: web.dev
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
A+Text CompressionAll text resources are compressedPASS
AImage Optimization11 images, 0 KB saveablePASS
Set explicit width and height to prevent CLS.
Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.
Source: web.dev / Core Web Vitals
A+JS Execution Cost393ms total JS executionPASS
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.googletagmanager.com/gtm.js?id=GTM-NDH95W87 | 154ms | 128ms | 17ms | 3rd |
| https://www.imperial.ac.uk/ | 117ms | 2ms | 0ms | 3rd |
| https://cdn-ukwest.onetrust.com/scripttemplates/202511.1.0/otBannerSdk.js | 62ms | 43ms | 9ms | 3rd |
| Unattributable | 60ms | 3ms | 0ms | 3rd |
A+Font Loading2 fonts (111 KB)PASS
Web fonts
2
111 KB total
Render-blocking
0
of 2
Dominant font-display
swap
Most common across fonts
Font loading timeline
- Convert to woff2 for ~30% smaller file size
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 ~4 KB and ~8 ms
A+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
Network Waterfall44 requests over 1017msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
Google Tag Manager www.googletagmanager.com | Tag Manager | 154ms | 191 KB | 35% | £2/mo | Optional |
www.imperial.ac.uk www.imperial.ac.uk | Other | 117ms | 11 KB | — | £1/mo | Optional |
cdn-ukwest.onetrust.com cdn-ukwest.onetrust.com | Other | 62ms | 124 KB | 52% | £1/mo | Optional |
Unattributable Unattributable | Other | 60ms | 0 KB | — | £1/mo | Optional |
100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.
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
52% of cdn-ukwest.onetrust.com's code is unused. The script may be loading features you don't use.
Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.
Source: web.dev