Performance
· 17 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.
6.95 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
20.12 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
455 ms
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.
8.35 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.
20.64 s
Page Load Progression
FPage Weight BudgetAction3.7 MB transferred, 65 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
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
CSS bundle is large — purge unused styles (PurgeCSS, Tailwind JIT) to reduce CSS payload.
Source: web.dev
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
DJS Execution CostAction2040ms total JS executionFIX
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.reading.ac.uk/homepage/web/files/dr-homepage/web-library.min.js | 407ms | 193ms | 15ms | 3rd |
| Unattributable | 355ms | 6ms | 0ms | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-TC325M | 351ms | 286ms | 61ms | 3rd |
| https://app.termly.io/resource-blocker/b846a047-fc56-4159-aaf3-7bdc36e97907 | 329ms | 263ms | 42ms | 3rd |
| https://www.reading.ac.uk/ | 175ms | 6ms | 2ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-11016496176&cx=c>m=4e64k0 | 121ms | 73ms | 48ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-13730620&cx=c>m=4e64k0 | 88ms | 54ms | 33ms | 3rd |
| https://www.reading.ac.uk/homepage/web/files/dr-homepage/js-modernizr.custom.04512.js | 77ms | 38ms | 1ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-13024755&cx=c>m=4e64k0 | 72ms | 42ms | 29ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-8556031&cx=c>m=4e64k0 | 65ms | 41ms | 24ms | 3rd |
FJS BundlesAction17 scripts, 621 KB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.reading.ac.uk/homepage/web/files/dr-homepage/web-library.min.js | 177 KB | 102 KB (58%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=AW-11016496176&cx=c>m=4e64k0 | 144 KB | 87 KB (61%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-13730620&cx=c>m=4e64k0 | 132 KB | 81 KB (61%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-13024755&cx=c>m=4e64k0 | 129 KB | 81 KB (62%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=DC-8556031&cx=c>m=4e64k0 | 129 KB | 80 KB (62%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-TC325M | 192 KB | 80 KB (41%) | ✓ | 3rd |
| https://www.reading.ac.uk/homepage/web/files/dr-homepage/js-jquery-2.1.1.js | 83 KB | 56 KB (68%) | ✓ | 3rd |
| https://app.termly.io/resource-blocker/b846a047-fc56-4159-aaf3-7bdc36e97907 | 143 KB | 54 KB (38%) | ✓ | 3rd |
| https://www.reading.ac.uk/homepage/web/files/dr-homepage/js-main.min.js | 1 KB | — | ✓ | 3rd |
| https://app.termly.io/resource-blocker/support/377-e518d8a5c599aa1c5977.min.js | 1 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
FPage Weight InventoryAction65 resources · 3.7 MB · 621 KB savings availableFIX
~621.1 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 65 resources | 3.7 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
CImage OptimizationAction26 images, 0 KB saveableREVIEW
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
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
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
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
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
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
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
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
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
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
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 Loading6 fonts (176 KB)PASS
Web fonts
6
176 KB total
Render-blocking
0
of 6
Dominant font-display
swap
Most common across fonts
Font loading timeline
- Convert to woff2 for ~30% smaller file size
- Convert to woff2 for ~30% smaller file size
- Convert to woff2 for ~30% smaller file size
- Convert to woff2 for ~30% smaller file size
- Convert to woff2 for ~30% smaller file size
- 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 ~53 KB and ~106 ms
A+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource Hints3 hints, 0 missing preconnectsPASS
Current Resource Hints
3 resource hints configured
A+Render-Blocking ResourcesNo render-blocking resources detectedPASS
A+Third-Party ResourcesNo third-party resources detectedPASS
Network Waterfall65 requests over 1148msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
www.reading.ac.uk www.reading.ac.uk | Other | 407ms | 177 KB | 58% | £4/mo | Costly |
Unattributable Unattributable | Other | 355ms | 0 KB | — | £4/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 351ms | 192 KB | 41% | £4/mo | Costly |
app.termly.io app.termly.io | Other | 329ms | 143 KB | 38% | £3/mo | Costly |
www.reading.ac.uk www.reading.ac.uk | Other | 175ms | 128 KB | — | £2/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 121ms | 144 KB | 61% | £1/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 88ms | 132 KB | 61% | £1/mo | Optional |
www.reading.ac.uk www.reading.ac.uk | Other | 77ms | 16 KB | — | £1/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 72ms | 129 KB | 62% | £1/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 65ms | 129 KB | 62% | £1/mo | Optional |
These scripts may cost more than they're worth
- www.reading.ac.uk adds 407ms and costs ~£4/month
- Unattributable adds 355ms and costs ~£4/month
- Google Tag Manager adds 351ms and costs ~£4/month
- app.termly.io adds 329ms 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.reading.ac.uk takes 407ms 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
58% of www.reading.ac.uk'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
Unattributable takes 355ms 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 351ms 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
app.termly.io takes 329ms 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
61% of Google Tag Manager'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
61% of Google Tag Manager'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
62% of Google Tag Manager'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
62% of Google Tag Manager'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