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.
1.35 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
3.36 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
114 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.
2.18 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.
3.97 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 sFPage Weight BudgetAction2.8 MB transferred, 43 requestsFIX
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
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
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
FJS BundlesAction12 scripts, 770 KB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/chunks/pages/_app-d691941104cf4a95.js | 1217 KB | 569 KB (47%) | ✓ | 3rd |
| https://tms.nationaltrust.org.uk/nationaltrust/prod/Bootstrap.js | 130 KB | 95 KB (74%) | ✓ | 3rd |
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/chunks/framework-23ec7355c2fecaf9.js | 88 KB | 45 KB (52%) | ✓ | 3rd |
| https://www.nationaltrust.org.uk/18f5227b-e27b-445a-a53f-f845fbe69b40/stormcaster.js | 165 KB | 40 KB (24%) | ✓ | 3rd |
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/chunks/main-06232a913dd19e0d.js | 44 KB | 21 KB (49%) | ✓ | 3rd |
| https://static.nationaltrust.org.uk/js/website-cookie-preferences-vue/nt-cookie-form.full.min.js | 37 KB | — | ✓ | 3rd |
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/chunks/webpack-6a6d4e7fd05f0de6.js | 2 KB | — | ✓ | 3rd |
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/chunks/pages/%5B%5B...route%5D%5D-0873afd79e1ed6fc.js | 1 KB | — | ✓ | 3rd |
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/bAfU8_wwySvyTYv782_ii/_buildManifest.js | 1 KB | — | ✓ | 3rd |
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/bAfU8_wwySvyTYv782_ii/_ssgManifest.js | 0 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 InventoryAction43 resources · 2.8 MB · 770 KB savings availableFIX
~770.3 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 43 resources | 2.8 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
BJS Execution Cost874ms total JS executionREVIEW
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/chunks/pages/_app-d691941104cf4a95.js | 255ms | 176ms | 72ms | 3rd |
| https://static.nationaltrust.org.uk/nt-front-end/_next/static/chunks/framework-23ec7355c2fecaf9.js | 190ms | 151ms | 7ms | 3rd |
| https://tms.nationaltrust.org.uk/nationaltrust/prod/Bootstrap.js | 125ms | 88ms | 36ms | 3rd |
| https://www.nationaltrust.org.uk/ | 121ms | 4ms | 1ms | 3rd |
| Unattributable | 102ms | 1ms | 0ms | 3rd |
| https://www.nationaltrust.org.uk/18f5227b-e27b-445a-a53f-f845fbe69b40/stormcaster.js | 81ms | 68ms | 7ms | 3rd |
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
A+Text CompressionAll text resources are compressedPASS
AImage Optimization23 images, 0 KB saveablePASS
A+Font Loading1 fonts (58 KB)PASS
Web fonts
1
58 KB total
Render-blocking
0
of 1
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 Waterfall43 requests over 3368msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
static.nationaltrust.org.uk static.nationaltrust.org.uk | Other | 255ms | 1217 KB | 47% | £3/mo | Costly |
static.nationaltrust.org.uk static.nationaltrust.org.uk | Other | 190ms | 88 KB | 52% | £2/mo | Optional |
tms.nationaltrust.org.uk tms.nationaltrust.org.uk | Other | 125ms | 130 KB | 74% | £1/mo | Optional |
www.nationaltrust.org.uk www.nationaltrust.org.uk | Other | 121ms | 122 KB | — | £1/mo | Optional |
Unattributable Unattributable | Other | 102ms | 0 KB | — | £1/mo | Optional |
www.nationaltrust.org.uk www.nationaltrust.org.uk | Other | 81ms | 165 KB | 24% | £1/mo | Optional |
These scripts may cost more than they're worth
- static.nationaltrust.org.uk adds 255ms 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
static.nationaltrust.org.uk takes 255ms 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
52% of static.nationaltrust.org.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
74% of tms.nationaltrust.org.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