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.
1.03 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
1.60 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
104 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.
1.74 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.
2.90 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 sDPage Weight BudgetAction2.3 MB transferred, 157 requestsFIX
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
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.
JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.
Source: web.dev
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.
Source: web.dev
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
DJS BundlesAction21 scripts, 326 KB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.googletagmanager.com/gtag/js?id=G-0E2CPWLEXN&cx=c>m=4e64h1 | 170 KB | 67 KB (40%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-16952590477&cx=c>m=4e64h1 | 145 KB | 64 KB (45%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-11919936&cx=c>m=4e64h1 | 129 KB | 59 KB (46%) | ✓ | 3rd |
| https://cc.cdn.civiccomputing.com/9/cookieControl-9.x.min.js | 123 KB | 56 KB (45%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-WXLX54 | 195 KB | 48 KB (25%) | ✓ | 3rd |
| https://script.crazyegg.com/pages/versioned/common-scripts/4ce8c7df8d425cc50464576824ed91eb.js | 55 KB | 31 KB (56%) | ✓ | 3rd |
| https://www.york.ac.uk/static/2/js/components/nav_mobile.js | 3 KB | — | ✓ | 3rd |
| https://dev.visualwebsiteoptimizer.com/dcdn/settings.js?a=890923&settings_type=4&ts=1776790816&dt=desktop&cc=US | 17 KB | — | ✓ | 3rd |
| https://www.york.ac.uk/static/2/js/components/course_search.js | 1 KB | — | ✓ | 3rd |
| https://dev.visualwebsiteoptimizer.com/cdn/edrv/worker-57f1b8d94a5f9167e9bcdcf861046428.br.js | 72 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 InventoryAction157 resources · 2.3 MB · 326 KB savings availableFIX
~325.9 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 157 resources | 2.3 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
BImage Optimization19 images, 0 KB saveableREVIEW
CJS Execution CostAction1515ms total JS executionREVIEW
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.york.ac.uk/ | 694ms | 288ms | 39ms | 3rd |
| Unattributable | 303ms | 10ms | 0ms | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-WXLX54 | 243ms | 178ms | 32ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=G-0E2CPWLEXN&cx=c>m=4e64h1 | 122ms | 109ms | 12ms | 3rd |
| https://script.crazyegg.com/pages/versioned/common-scripts/4ce8c7df8d425cc50464576824ed91eb.js | 87ms | 72ms | 9ms | 3rd |
| https://cc.cdn.civiccomputing.com/9/cookieControl-9.x.min.js | 65ms | 56ms | 9ms | 3rd |
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
A+Text CompressionAll text resources are compressedPASS
A+Font Loading4 fonts (152 KB)PASS
Web fonts
4
152 KB total
Render-blocking
0
of 4
Dominant font-display
swap
Most common across fonts
Font loading timeline
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 CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
Network Waterfall157 requests over 2999msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
www.york.ac.uk www.york.ac.uk | Other | 694ms | 11 KB | — | £7/mo | Costly |
Unattributable Unattributable | Other | 303ms | 0 KB | — | £3/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 243ms | 195 KB | 25% | £3/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 122ms | 170 KB | 40% | £1/mo | Optional |
script.crazyegg.com script.crazyegg.com | Other | 87ms | 55 KB | 56% | £1/mo | Optional |
cc.cdn.civiccomputing.com cc.cdn.civiccomputing.com | Other | 65ms | 123 KB | 45% | £1/mo | Optional |
These scripts may cost more than they're worth
- www.york.ac.uk adds 694ms and costs ~£7/month
- Unattributable adds 303ms and costs ~£3/month
- Google Tag Manager adds 243ms and costs ~£3/month
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
www.york.ac.uk takes 694ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
Unattributable takes 303ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
Google Tag Manager takes 243ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.
This script has high main-thread execution time — optimize hot paths or defer.
Source: web.dev
56% of script.crazyegg.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