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.
5.79 s
Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.
17.71 s
Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.
16.31 s
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.
14.46 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.
35.14 s
Page Load Progression
FPage Weight BudgetAction4.7 MB transferred, 178 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
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
DThird-Party ImpactAction100% third-party, 0 ms blockingFIX
FJS Execution CostAction33485ms total JS executionFIX
Main Thread Breakdown
| Script | Total | Scripting | Parse/Compile | Party |
|---|---|---|---|---|
| https://www.googletagmanager.com/gtm.js?id=GTM-THZ5TQF>m=4e64k1h2 | 5359ms | 4435ms | 119ms | 3rd |
| https://www.boots.com/ils-Moth-a-bluntry-owes-and-to-they-Thunds-till-/9744024032794688957?s=BVFW77gR | 4865ms | 4403ms | 143ms | 3rd |
| https://www.boots.com/ | 3436ms | 932ms | 94ms | 3rd |
| https://www.boots.com/assets/vendor-bundle-f74ea760.js | 2431ms | 426ms | 245ms | 3rd |
| https://www.boots.com/assets/main-bundle-2489f758.js | 2392ms | 1848ms | 7ms | 3rd |
| Unattributable | 2241ms | 357ms | 0ms | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-MKCRTH2>m=4e64k1h2 | 1788ms | 1658ms | 72ms | 3rd |
| https://www.boots.com/deot-thath-I-my-bothinke-you-weywarley-violent-C | 1217ms | 956ms | 148ms | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-W26C7Q2 | 1128ms | 813ms | 243ms | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-5T524KG>m=4e64k1h2 | 782ms | 694ms | 72ms | 3rd |
Showing top 10 of 38 scripts
FJS BundlesAction65 scripts, 1.2 MB unusedFIX
Downloaded but never executed on this page.
| Script | Size | Unused | Minified | Party |
|---|---|---|---|---|
| https://www.boots.com/assets/vendor-bundle-f74ea760.js | 393 KB | 202 KB (51%) | ✓ | 3rd |
| https://cdns.gigya.com/js/gigya.js?apikey=3_tgWZjPmf4Y0eeO0Okf-Cl3OjuaTNMW5aSIYEi0dY66KmwQXWyItwHA1Kb_uGmB9r | 239 KB | 137 KB (58%) | ✓ | 3rd |
| https://www.boots.com/wcsstore/eBootsStorefrontAssetStore/javascript/generated/Common.min.js | 84 KB | 78 KB (93%) | ✓ | 3rd |
| https://www.boots.com/wcsstore/dojo18/dojo/dojodesktop-rwd.js | 106 KB | 78 KB (73%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/destination?id=DC-10359038&cx=c>m=4e64k1h2 | 130 KB | 65 KB (50%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-MKCRTH2>m=4e64k1h2 | 141 KB | 65 KB (46%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-M48LDLD>m=4e64k1h2 | 159 KB | 64 KB (40%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/destination?id=DC-8054130&cx=c>m=4e64k1h2 | 131 KB | 64 KB (48%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtm.js?id=GTM-5T524KG>m=4e64k1h2 | 144 KB | 63 KB (44%) | ✓ | 3rd |
| https://www.googletagmanager.com/gtag/destination?id=AW-986212917&cx=c>m=4e64k1h2 | 146 KB | 62 KB (42%) | ✓ | 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 InventoryAction178 resources · 4.7 MB · 1.2 MB savings availableFIX
~1.2 MiB of savings available
| # | Resource | Type | Size | Cache | Unused | 3rd party | Issues |
|---|---|---|---|---|---|---|---|
| — | — | ||||||
| 178 resources | 4.7 MiB | ||||||
FHTTP CachingActionNo cache headersFIX
No Cache-Control header
Adding a Cache-Control header can significantly improve repeat-visit performance.
CImage OptimizationAction37 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
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 Loading9 fonts (288 KB)PASS
Web fonts
9
288 KB total
Render-blocking
0
of 9
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
- 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 ~86 KB and ~172 ms
A+Resource CachingAll resources properly cachedPASS
A+Critical Rendering PathNo render-blocking resourcesPASS
A+Resource HintsNo optimization neededPASS
A+Render-Blocking ResourcesNo render-blocking resources detectedPASS
A+Third-Party ResourcesNo third-party resources detectedPASS
Network Waterfall178 requests over 8893msINFO
Third-Party Script CostPer-script blocking time, transfer cost, and cache headersINFO
| Script | Category | Execution | Transfer | Unused | Monthly Cost | Verdict |
|---|---|---|---|---|---|---|
Google Tag Manager www.googletagmanager.com | Tag Manager | 5359ms | 174 KB | 27% | £56/mo | Costly |
www.boots.com www.boots.com | Other | 4865ms | 247 KB | — | £50/mo | Costly |
www.boots.com www.boots.com | Other | 3436ms | 135 KB | — | £36/mo | Costly |
www.boots.com www.boots.com | Other | 2431ms | 393 KB | 51% | £25/mo | Costly |
www.boots.com www.boots.com | Other | 2392ms | 7 KB | — | £25/mo | Costly |
Unattributable Unattributable | Other | 2241ms | 0 KB | — | £23/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 1788ms | 141 KB | 46% | £19/mo | Costly |
www.boots.com www.boots.com | Other | 1217ms | 240 KB | 11% | £13/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 1128ms | 130 KB | 43% | £12/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 782ms | 144 KB | 44% | £8/mo | Costly |
cdns.gigya.com cdns.gigya.com | Other | 722ms | 239 KB | 58% | £7/mo | Costly |
www.boots.com www.boots.com | Other | 708ms | 79 KB | 37% | £7/mo | Costly |
www.boots.com www.boots.com | Other | 665ms | 2 KB | — | £7/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 624ms | 146 KB | 42% | £6/mo | Costly |
w.usabilla.com w.usabilla.com | Other | 454ms | 32 KB | — | £5/mo | Costly |
OneTrust cdn.cookielaw.org | Consent | 428ms | 82 KB | 43% | £4/mo | Essential |
Google Tag Manager www.googletagmanager.com | Tag Manager | 409ms | 131 KB | 48% | £4/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 399ms | 159 KB | 40% | £4/mo | Costly |
www.uqd.io www.uqd.io | Other | 393ms | 29 KB | — | £4/mo | Costly |
OneTrust cdn.cookielaw.org | Consent | 377ms | 9 KB | — | £4/mo | Essential |
Google Tag Manager www.googletagmanager.com | Tag Manager | 376ms | 169 KB | 35% | £4/mo | Costly |
Google Tag Manager www.googletagmanager.com | Tag Manager | 304ms | 130 KB | 50% | £3/mo | Costly |
www.boots.com www.boots.com | Other | 250ms | 84 KB | 93% | £3/mo | Costly |
www.boots.com www.boots.com | Other | 186ms | 33 KB | — | £2/mo | Optional |
account.boots.com account.boots.com | Other | 176ms | 0 KB | — | £2/mo | Optional |
www.boots.com www.boots.com | Other | 162ms | 106 KB | 73% | £2/mo | Optional |
www.boots.com www.boots.com | Other | 150ms | 31 KB | — | £2/mo | Optional |
www.boots.com www.boots.com | Other | 139ms | 35 KB | 66% | £1/mo | Optional |
t.promotionx.io t.promotionx.io | Other | 138ms | 39 KB | 59% | £1/mo | Optional |
account.boots.com account.boots.com | Other | 136ms | 0 KB | — | £1/mo | Optional |
assets.boots.com assets.boots.com | Other | 123ms | 50 KB | 61% | £1/mo | Optional |
account.boots.com account.boots.com | Other | 98ms | 0 KB | — | £1/mo | Optional |
account.boots.com account.boots.com | Other | 97ms | 0 KB | — | £1/mo | Optional |
www.boots.com www.boots.com | Other | 82ms | 23 KB | — | £1/mo | Optional |
cdn.synthetix.com cdn.synthetix.com | Other | 78ms | 7 KB | — | £1/mo | Optional |
account.boots.com account.boots.com | Other | 60ms | 56 KB | — | £1/mo | Optional |
cdn.synthetix.com cdn.synthetix.com | Other | 60ms | 14 KB | — | £1/mo | Optional |
www.boots.com www.boots.com | Other | 53ms | 90 KB | — | £1/mo | Optional |
These scripts may cost more than they're worth
- Google Tag Manager adds 5359ms and costs ~£56/month
- www.boots.com adds 4865ms and costs ~£50/month
- www.boots.com adds 3436ms and costs ~£36/month
- www.boots.com adds 2431ms and costs ~£25/month
- www.boots.com adds 2392ms and costs ~£25/month
- Unattributable adds 2241ms and costs ~£23/month
- Google Tag Manager adds 1788ms and costs ~£19/month
- www.boots.com adds 1217ms and costs ~£13/month
- Google Tag Manager adds 1128ms and costs ~£12/month
- Google Tag Manager adds 782ms and costs ~£8/month
- cdns.gigya.com adds 722ms and costs ~£7/month
- www.boots.com adds 708ms and costs ~£7/month
- www.boots.com adds 665ms and costs ~£7/month
- Google Tag Manager adds 624ms and costs ~£6/month
- w.usabilla.com adds 454ms and costs ~£5/month
- Google Tag Manager adds 409ms and costs ~£4/month
- Google Tag Manager adds 399ms and costs ~£4/month
- www.uqd.io adds 393ms and costs ~£4/month
- Google Tag Manager adds 376ms and costs ~£4/month
- Google Tag Manager adds 304ms and costs ~£3/month
- www.boots.com adds 250ms 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
Google Tag Manager takes 5359ms 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.boots.com takes 4865ms 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.boots.com takes 3436ms 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.boots.com takes 2431ms 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
51% of www.boots.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
www.boots.com takes 2392ms 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 2241ms 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 1788ms 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.boots.com takes 1217ms 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 1128ms 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 782ms 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
cdns.gigya.com takes 722ms 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 cdns.gigya.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
www.boots.com takes 708ms 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.boots.com takes 665ms 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 624ms 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
w.usabilla.com takes 454ms 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 409ms 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 399ms 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.uqd.io takes 393ms 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 376ms 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 304ms 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.boots.com takes 250ms 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
93% of www.boots.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
73% of www.boots.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
66% of www.boots.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
59% of t.promotionx.io'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 assets.boots.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