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.
610 ms
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
2.57 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
100 ms
Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.
0.002
Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.
1.39 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.
2.61 s
Page Load Progression
FPage Weight BudgetAction3.5 MB transferred, 66 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
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
FJS BundlesAction25 scripts, 935 KB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.gstatic.com/recaptcha/releases/gTpTIWhbKpxADzTzkcabhXN4/recaptcha__en.js | 0 KB | 177 KB (49%) | ✓ | 3rd |
| https://www.gstatic.com/recaptcha/releases/gTpTIWhbKpxADzTzkcabhXN4/recaptcha__en.js | 0 KB | 177 KB (49%) | ✓ | 3rd |
| https://www.gstatic.com/recaptcha/releases/gTpTIWhbKpxADzTzkcabhXN4/recaptcha__en.js | 362 KB | 177 KB (49%) | ✓ | 3rd |
| https://www.gstatic.com/recaptcha/releases/gTpTIWhbKpxADzTzkcabhXN4/recaptcha__en.js | 362 KB | 177 KB (49%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/js?id=G-PY4SWZN1RJ&cx=c>m=4e64k0 | 177 KB | 70 KB (40%) | ✓ | 3rd |
| https://cc.cdn.civiccomputing.com/9/cookieControl-9.x.min.js | 123 KB | 57 KB (47%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-KXBTQP | 146 KB | 57 KB (39%) | ✓ | 3rd |
| https://www.london.gov.uk/sites/default/files/js/js_Qpd3_8zaD-ktIGtr4DPlEy9NulKx34S2UQq7EcgOsRI.js?scope=footer&delta=0&language=en&theme=gla_lgov&include=eJyFkt1y3CAMhV_ImOs-DSMLLVYDiAHF3vTpi7dN2NTr6QU_-s5hQELIGyOKvDGhZK0SLZ7Q3EiVc2jTWXth_zF5UIjwQdUutMLGUtsUIjiUSm7bxfbxANQUlJxWyC2CsmT7Gj_cMchmF1GVZBBilHcdHKH6Ed34bvppL4kbeXOTmgz7NgwrVTGcINBgnKmqKRI_bhzj4BEWiubxpgGTeKqZf9WBPk8algF77UzDXpZoCnjfy2hUyit9gWp29ro-iaxkVoJ-1YD7Cmo4l6fsHSLa52B8WRAJsdcSgg19-jee4Sfcv8M0VUIoiivYP8L8BRzlJ_VrNzWCiquDwg7eVVBSiaRkL_i0Me3NHX3i6F6kqj2Raafl-Df7d509Q5RwwhQpUdYZV8K3Re7ULi2eFDi2ucFG_zWphJ76pS1Ra0f3XOlSjr69fkvrGzwneUy_Ab6VZgc | 64 KB | 43 KB (68%) | ✓ | 3rd |
| https://www.google.com/recaptcha/api.js?hl=en&render=explicit&onload=drupalRecaptchaOnload | 1 KB | — | ✓ | 3rd |
| https://unpkg.com/headroom.js@0.12.0/dist/headroom.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
FPage Weight InventoryAction66 resources · 3.5 MB · 935 KB savings availableFIX
~934.7 KiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 66 resources | 3.5 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
BImage Optimization21 images, 0 KB saveableREVIEW
CJS Execution CostAction1315ms total JS executionREVIEW
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.gstatic.com/recaptcha/releases/gTpTIWhbKpxADzTzkcabhXN4/recaptcha__en.js | 261ms | 226ms | 29ms | 3rd |
| https://www.london.gov.uk/sites/default/files/js/js_plCzwTyou4p__J_-HnwJiYf6_PBOkCV4lch7VBIp9T4.js?scope=footer&delta=4&language=en&theme=gla_lgov&include=eJyFkt1y3CAMhV_ImOs-DSMLLVYDiAHF3vTpi7dN2NTr6QU_-s5hQELIGyOKvDGhZK0SLZ7Q3EiVc2jTWXth_zF5UIjwQdUutMLGUtsUIjiUSm7bxfbxANQUlJxWyC2CsmT7Gj_cMchmF1GVZBBilHcdHKH6Ed34bvppL4kbeXOTmgz7NgwrVTGcINBgnKmqKRI_bhzj4BEWiubxpgGTeKqZf9WBPk8algF77UzDXpZoCnjfy2hUyit9gWp29ro-iaxkVoJ-1YD7Cmo4l6fsHSLa52B8WRAJsdcSgg19-jee4Sfcv8M0VUIoiivYP8L8BRzlJ_VrNzWCiquDwg7eVVBSiaRkL_i0Me3NHX3i6F6kqj2Raafl-Df7d509Q5RwwhQpUdYZV8K3Re7ULi2eFDi2ucFG_zWphJ76pS1Ra0f3XOlSjr69fkvrGzwneUy_Ab6VZgc | 196ms | 35ms | 1ms | 3rd |
| Unattributable | 163ms | 9ms | 0ms | 3rd |
| https://www.googletagmanager.com/gtag/js?id=G-PY4SWZN1RJ&cx=c>m=4e64k0 | 136ms | 117ms | 17ms | 3rd |
| https://www.london.gov.uk/themes/custom/gla_lgov/libraries/alpinejs/dist/cdn.js?tdu3wa | 119ms | 96ms | 3ms | 3rd |
| https://www.london.gov.uk/ | 109ms | 9ms | 1ms | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-KXBTQP | 97ms | 79ms | 15ms | 3rd |
| https://www.london.gov.uk/sites/default/files/js/js_Qpd3_8zaD-ktIGtr4DPlEy9NulKx34S2UQq7EcgOsRI.js?scope=footer&delta=0&language=en&theme=gla_lgov&include=eJyFkt1y3CAMhV_ImOs-DSMLLVYDiAHF3vTpi7dN2NTr6QU_-s5hQELIGyOKvDGhZK0SLZ7Q3EiVc2jTWXth_zF5UIjwQdUutMLGUtsUIjiUSm7bxfbxANQUlJxWyC2CsmT7Gj_cMchmF1GVZBBilHcdHKH6Ed34bvppL4kbeXOTmgz7NgwrVTGcINBgnKmqKRI_bhzj4BEWiubxpgGTeKqZf9WBPk8algF77UzDXpZoCnjfy2hUyit9gWp29ro-iaxkVoJ-1YD7Cmo4l6fsHSLa52B8WRAJsdcSgg19-jee4Sfcv8M0VUIoiivYP8L8BRzlJ_VrNzWCiquDwg7eVVBSiaRkL_i0Me3NHX3i6F6kqj2Raafl-Df7d509Q5RwwhQpUdYZV8K3Re7ULi2eFDi2ucFG_zWphJ76pS1Ra0f3XOlSjr69fkvrGzwneUy_Ab6VZgc | 80ms | 65ms | 6ms | 3rd |
| https://scripts.clarity.ms/0.8.59/clarity.js | 79ms | 68ms | 3ms | 3rd |
| https://cc.cdn.civiccomputing.com/9/cookieControl-9.x.min.js | 76ms | 61ms | 13ms | 3rd |
A+Text CompressionAll text resources are compressedPASS
A+Font Loading2 fonts (34 KB)PASS
Web fonts
2
34 KB total
Render-blocking
0
of 2
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
A+Green HostingWhether the site is served from green-energy infrastructurePASS
Green Hosting
This site is hosted on green energy infrastructure
Provider: Cloudflare
Network Waterfall66 requests over 3730msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
www.gstatic.com www.gstatic.com | Other | 261ms | 0 KB | 49% | £3/mo | Costly |
www.london.gov.uk www.london.gov.uk | Other | 196ms | 14 KB | — | £2/mo | Optional |
Unattributable Unattributable | Other | 163ms | 0 KB | — | £2/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 136ms | 177 KB | 40% | £1/mo | Optional |
www.london.gov.uk www.london.gov.uk | Other | 119ms | 25 KB | — | £1/mo | Optional |
www.london.gov.uk www.london.gov.uk | Other | 109ms | 31 KB | — | £1/mo | Optional |
Google Tag Manager www.googletagmanager.com | Tag Manager | 97ms | 146 KB | 39% | £1/mo | Optional |
www.london.gov.uk www.london.gov.uk | Other | 80ms | 64 KB | 68% | £1/mo | Optional |
Microsoft Clarity scripts.clarity.ms | Session Replay | 79ms | 26 KB | — | £1/mo | Optional |
cc.cdn.civiccomputing.com cc.cdn.civiccomputing.com | Other | 76ms | 123 KB | 47% | £1/mo | Optional |
These scripts may cost more than they're worth
- www.gstatic.com adds 261ms 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.gstatic.com takes 261ms 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
68% of www.london.gov.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