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.
1.96 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
4.16 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
456 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.
4.20 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.
13.14 s
Page Load Progression
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
DJS Execution CostAction2808ms total JS executionFIX
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.metoffice.gov.uk/webfiles/1764673469274/js/minified/homepage.min.js | 573ms | 512ms | 2ms | 3rd |
| Unattributable | 528ms | 9ms | 0ms | 3rd |
| https://www.metoffice.gov.uk/ | 474ms | 11ms | 4ms | 3rd |
| https://players.brightcove.net/2310970326001/Yk2siaFBf_default/index.min.js | 323ms | 162ms | 136ms | 3rd |
| https://www.metoffice.gov.uk/public/gdpr-consent/cookieControl-config.js?1764673469274 | 257ms | 130ms | 1ms | 3rd |
| https://cc.cdn.civiccomputing.com/9/cookieControl-9.11.min.js | 191ms | 156ms | 34ms | 3rd |
| https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.6/require.min.js | 180ms | 144ms | 2ms | 3rd |
| https://imasdk.googleapis.com/js/sdkloader/ima3_debug.js | 124ms | 84ms | 38ms | 3rd |
| https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.7.1/leaflet.js | 97ms | 26ms | 9ms | 3rd |
| https://pagead2.googlesyndication.com/omsdk/releases/live/omweb-v1.js | 62ms | 57ms | 3ms | 3rd |
DJS BundlesAction49 scripts, 363 KB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://players.brightcove.net/2310970326001/Yk2siaFBf_default/index.min.js | 326 KB | 188 KB (58%) | ✓ | 3rd |
| https://imasdk.googleapis.com/js/sdkloader/ima3_debug.js | 160 KB | 102 KB (64%) | ✓ | 3rd |
| https://cc.cdn.civiccomputing.com/9/cookieControl-9.11.min.js | 123 KB | 52 KB (42%) | ✓ | 3rd |
| https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.7.1/leaflet.js | 35 KB | 22 KB (62%) | ✓ | 3rd |
| https://www.metoffice.gov.uk/webfiles/1764673469274/js/mapping/map/map.js | 2 KB | — | ✓ | 3rd |
| https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.6/require.min.js | 6 KB | — | ✓ | 3rd |
| https://www.metoffice.gov.uk/webfiles/1764673469274/js/common/geohash-location.js | 1 KB | — | ✓ | 3rd |
| https://www.metoffice.gov.uk/webfiles/1764673469274/js/minified/global.min.js | 9 KB | — | ✓ | 3rd |
| https://cdnjs.cloudflare.com/ajax/libs/iamdustan-smoothscroll/0.4.0/smoothscroll.min.js | 2 KB | — | ✓ | 3rd |
| https://www.metoffice.gov.uk/webfiles/1764673469274/js/common/run-scripts-requiring-consent.js | 2 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
DPage Weight InventoryAction111 resources · 1.9 MB · 363 KB savings availableFIX
~363.3 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 111 resources | 1.9 MiB | ||||||
CPage Weight BudgetAction1.9 MB transferred, 111 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
Subset fonts to include only used characters, or switch to system font stacks.
Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).
Source: web.dev font loading
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
BImage Optimization30 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
CGreen HostingActionWhether the site is served from green-energy infrastructureREVIEW
Green Hosting
No green hosting detected
BHTTP Cachingmax-age=0REVIEW
max-age=0
| Directive | Value | Meaning |
|---|---|---|
| max-age | 0 | Cache for 0 seconds |
A+Text CompressionAll text resources are compressedPASS
A+Font Loading5 fonts (303 KB)PASS
Web fonts
5
303 KB total
Render-blocking
0
of 5
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
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 ~91 KB and ~182 ms
A+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource Hints14 hints, 0 missing preconnectsPASS
Current Resource Hints
14 resource hints configured
A+Render-Blocking ResourcesNo render-blocking resources detectedPASS
A+Third-Party ResourcesNo third-party resources detectedPASS
Network Waterfall111 requests over 1091msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
www.metoffice.gov.uk www.metoffice.gov.uk | Other | 573ms | 4 KB | — | £6/mo | Costly |
Unattributable Unattributable | Other | 528ms | 0 KB | — | £5/mo | Costly |
www.metoffice.gov.uk www.metoffice.gov.uk | Other | 474ms | 15 KB | — | £5/mo | Costly |
players.brightcove.net players.brightcove.net | Other | 323ms | 326 KB | 58% | £3/mo | Costly |
www.metoffice.gov.uk www.metoffice.gov.uk | Other | 257ms | 2 KB | — | £3/mo | Costly |
cc.cdn.civiccomputing.com cc.cdn.civiccomputing.com | Other | 191ms | 123 KB | 42% | £2/mo | Optional |
cdnjs cdnjs.cloudflare.com | CDN | 180ms | 6 KB | — | £2/mo | Optional |
imasdk.googleapis.com imasdk.googleapis.com | Other | 124ms | 160 KB | 64% | £1/mo | Optional |
cdnjs cdnjs.cloudflare.com | CDN | 97ms | 35 KB | 62% | £1/mo | Optional |
pagead2.googlesyndication.com pagead2.googlesyndication.com | Other | 62ms | 15 KB | — | £1/mo | Optional |
These scripts may cost more than they're worth
- www.metoffice.gov.uk adds 573ms and costs ~£6/month
- Unattributable adds 528ms and costs ~£5/month
- www.metoffice.gov.uk adds 474ms and costs ~£5/month
- players.brightcove.net adds 323ms and costs ~£3/month
- www.metoffice.gov.uk adds 257ms 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.metoffice.gov.uk takes 573ms 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 528ms 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
www.metoffice.gov.uk takes 474ms 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
players.brightcove.net takes 323ms 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 players.brightcove.net'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
www.metoffice.gov.uk takes 257ms 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
64% of imasdk.googleapis.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
62% of cdnjs'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