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https://www.zalando.com

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
69
GRADE
D
FIX
5
REVIEW
2
PASS
5
INFO
2

Performance-focused optimization plan with CWV assessment, top offenders, and time estimates

Mobile Desktop
35
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
95
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
81
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
92
SEO Measures basic SEO optimizations: meta tags, crawlability, link text, and mobile friendliness.

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

4.03 s

Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.

9.12 s

Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.

1.47 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.

6.80 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.

18.76 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 s
Checks
14
5 PASS 2 REVIEW 5 FIX
F
Page Weight Budget
Action
2.8 MB transferred, 115 requests
FIX
2.8 MB transferred, 115 requests
Warning::
Page weighs 8.3 MB (2.8 MB transferred)
Warning::
JavaScript is 1.8 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.8 MB
Info::
Fonts are 203 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 203 KB
Warning::
115 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.58 g CO2 per page load
2.8 MB / 2.4 MB budget
2.8 MB transferred
115 requests
0.58 g CO2 per page load
JavaScript 1.8 MiB 64%
Images 566.7 KiB 20%
Fonts 203.5 KiB 7%
Other 109.9 KiB 4%
HTML 105.5 KiB 4%
CSS 48.9 KiB 2%
Other 3.5 KiB 0%
Other 2.4 KiB 0%
Other 0 B 0%
0 2.4 MB 4.9 MB
Over budget

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Why this matters

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.

Why this matters

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.

Why this matters

High HTTP request count — bundling, sprite-ing, and HTTP/2 server push can reduce per-request overhead.

Source: web.dev

D
Third-Party Impact
Action
100% third-party, 0 ms blocking
FIX
100% third-party, 0 ms blocking
Warning::
Third-party code accounts for 100% of page weight (2.8 MiB of 2.8 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Execution Cost
Action
7464ms total JS execution
FIX
7464ms total JS execution
Warning::
https://mosaic01.ztat.net/base-assets/9-1-0/requir...: 1128ms CPU time
Warning::
Unattributable: 1112ms CPU time
Warning::
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/SQOS...: 1052ms CPU time
Warning::
https://mosaic01.ztat.net/base-assets/9-1-0/assets...: 1012ms CPU time
Warning::
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/JiOS...: 788ms CPU time
Warning::
Third-party scripts: 7464ms (100% of total)

Main Thread Breakdown

Script Evaluation 69% Other 13% Script Parsing & Compilation 7% Style & Layout 4%
ScriptTotalScriptingParse/CompileParty
https://mosaic01.ztat.net/base-assets/9-1-0/require-2.1.22.min.js1128ms1087ms3ms3rd
Unattributable1112ms280ms0ms3rd
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/SQOSfQaLYL/ejJ9ETIaAwk/ASh/6HHE5dF9v?v=079283cf-5501-393e-8730-1ef1d81e02101052ms971ms38ms3rd
https://mosaic01.ztat.net/base-assets/9-1-0/assets/bundle.js1012ms816ms19ms3rd
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/JiOSfQ8rYLbtbrmi/IntzETIaAwk/L1Q/vSStVYQkC788ms721ms51ms3rd
https://www.zalando.es/736ms53ms54ms3rd
https://mosaic01.ztat.net/pnl/gtag/js?id=G-MDW1S9PQPW&l=dataLayerGA4429ms370ms54ms3rd
https://app.usercentrics.eu/browser-ui/3.97.0/index.module.js350ms264ms2ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-T3W9FX&l=dataLayer345ms294ms43ms3rd
https://www.zalando.es/akam/13/54f5f335131ms123ms4ms3rd

Showing top 10 of 14 scripts

F
JS Bundles
Action
43 scripts, 736 KB unused
FIX
43 scripts, 736 KB unused
Warning::
https://mosaic03.ztat.net/seo/glados/96356a7214383...: 198 KB unused (85%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://mosaic02.ztat.net/rnd/ng/re-common-chunk/i...: 116 KB unused (69%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-T3W...: 74 KB unused (50%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=AW-100...: 65 KB unused (46%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://mosaic01.ztat.net/pnl/gtag/js?id=G-MDW1S9P...: 59 KB unused (35%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 736 KB
736 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://mosaic03.ztat.net/seo/glados/96356a721438313ca54d-main.js233 KB198 KB (85%)✓3rd
https://mosaic02.ztat.net/rnd/ng/re-common-chunk/index-817b9f04541319db5fad.js168 KB116 KB (69%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-T3W9FX&l=dataLayer150 KB74 KB (50%)✓3rd
https://www.googletagmanager.com/gtag/js?id=AW-1006368194&cx=c&gtm=4e6481143 KB65 KB (46%)✓3rd
https://mosaic01.ztat.net/pnl/gtag/js?id=G-MDW1S9PQPW&l=dataLayerGA4170 KB59 KB (35%)✓3rd
https://app.usercentrics.eu/browser-ui/3.97.0/index.module.js120 KB54 KB (45%)✓3rd
https://mosaic02.ztat.net/rnd/ng/runtime-concurrent-617c06d4622ad527ee13.js157 KB48 KB (31%)✓3rd
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/JiOSfQ8rYLbtbrmi/IntzETIaAwk/L1Q/vSStVYQkC185 KB39 KB (21%)✓3rd
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/SQOSfQaLYL/ejJ9ETIaAwk/ASh/6HHE5dF9v?v=079283cf-5501-393e-8730-1ef1d81e0210158 KB31 KB (20%)✓3rd
https://app.usercentrics.eu/browser-ui/3.97.0/VirtualServiceItem-39329dba.js49 KB26 KB (54%)✓3rd

Consider code splitting or tree shaking to reduce unused code.

Why this matters

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.

Why this matters

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.

Why this matters

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.

Why this matters

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.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

F
HTTP Caching
Action
No cache headers
FIX
No cache headers
Warning::
No Cache-Control header found
Browsers will use heuristic caching, which can be unpredictable. Set explicit cache headers.

No Cache-Control header

Adding a Cache-Control header can significantly improve repeat-visit performance.

B
Image Optimization
26 images, 0 KB saveable
REVIEW
26 images, 0 KB saveable
Info::
All images are well-optimized
26 images 567 KB
0 oversized -0 KB
18 legacy format
0 missing dimensions CLS risk
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Text Compression
All text resources are compressed
PASS
All text resources are compressed
Info::
All text resources are compressed
All text resources are properly compressed.
A+
Font Loading
3 fonts (203 KB)
PASS
3 fonts (203 KB)
Info::
3 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

3

203 KB total

Render-blocking

0

of 3

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s 6.0 s 7.0 s 8.0 s 9.0 s FCP 4.0 s LCP 9.1 shttps://mosaic02.ztat.net/zds/assets/fonts/ZalandoSans[wdth,wght].ba6fc11d.woff2ZalandoSans[wdth,wght].... https://mosaic02.ztat.net/zds/assets/fonts/ZalandoSans[wdth,wght].ba6fc11d.woff2 — 93.5 KiB — 0 ms — font-display: swaphttps://mosaic01.ztat.net/zds/assets/fonts/867e79d.woff2867e79d.woff2 https://mosaic01.ztat.net/zds/assets/fonts/867e79d.woff2 — 58.5 KiB — 0 ms — font-display: swaphttps://mosaic01.ztat.net/zds/assets/fonts/76a99f7.woff276a99f7.woff2 https://mosaic01.ztat.net/zds/assets/fonts/76a99f7.woff2 — 51.5 KiB — 0 ms — font-display: swap
ZalandoSans[wdth,wght].... woff2 swap
Size 94 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
867e79d.woff2 woff2 swap
Size 58 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
76a99f7.woff2 woff2 swap
Size 52 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
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 Caching
All resources properly cached
PASS
All resources properly cached
Info::
No caching issues found
All static resources have appropriate caching headers.
A+
Critical Rendering Path
No render-blocking resources
PASS
No render-blocking resources
Info::
No render-blocking resources detected
A+
Resource Hints
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
Network Waterfall
115 requests over 0ms
INFO

Performance analysis not available for this result.

Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
100% of JavaScript execution is third-party
First-party Third-party 7464ms · 1502KB · $99/mo
mosaic01.ztat.net
Other
Costly
Execution 1128ms
Transfer 8 KB
Monthly Cost $15/mo
Unattributable
Other
Costly
Execution 1112ms
Transfer 0 KB
Monthly Cost $15/mo
www.zalando.es
Other
Costly
Execution 1052ms
Transfer 158 KB
Unused 20%
Monthly Cost $14/mo
mosaic01.ztat.net
Other
Costly
Execution 1012ms
Transfer 80 KB
Unused 30%
Monthly Cost $13/mo
www.zalando.es
Other
Costly
Execution 788ms
Transfer 1 KB
Unused 21%
Monthly Cost $10/mo
www.zalando.es
Other
Costly
Execution 736ms
Transfer 103 KB
Monthly Cost $10/mo
mosaic01.ztat.net
Other
Costly
Execution 429ms
Transfer 170 KB
Unused 35%
Monthly Cost $6/mo
app.usercentrics.eu
Other
Costly
Execution 350ms
Transfer 120 KB
Unused 45%
Monthly Cost $5/mo
Google Tag Manager
Tag Manager
Costly
Execution 345ms
Transfer 150 KB
Unused 50%
Monthly Cost $5/mo
www.zalando.es
Other
Optional
Execution 131ms
Transfer 9 KB
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 130ms
Transfer 143 KB
Unused 46%
Monthly Cost $2/mo
mosaic02.ztat.net
Other
Optional
Execution 105ms
Transfer 157 KB
Unused 31%
Monthly Cost $1/mo
mosaic03.ztat.net
Other
Optional
Execution 94ms
Transfer 233 KB
Unused 85%
Monthly Cost $1/mo
mosaic02.ztat.net
Other
Optional
Execution 51ms
Transfer 168 KB
Unused 69%
Monthly Cost $1/mo

These scripts may cost more than they're worth

  • mosaic01.ztat.net adds 1128ms and costs ~$15/month
  • Unattributable adds 1112ms and costs ~$15/month
  • www.zalando.es adds 1052ms and costs ~$14/month
  • mosaic01.ztat.net adds 1012ms and costs ~$13/month
  • www.zalando.es adds 788ms and costs ~$10/month
  • www.zalando.es adds 736ms and costs ~$10/month
  • mosaic01.ztat.net adds 429ms and costs ~$6/month
  • app.usercentrics.eu adds 350ms and costs ~$5/month
  • Google Tag Manager adds 345ms and costs ~$5/month

100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.

Why this matters

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

mosaic01.ztat.net takes 1128ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

Unattributable takes 1112ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

www.zalando.es takes 1052ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

mosaic01.ztat.net takes 1012ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

www.zalando.es takes 788ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

www.zalando.es takes 736ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

mosaic01.ztat.net takes 429ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

app.usercentrics.eu takes 350ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

Google Tag Manager takes 345ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

85% of mosaic03.ztat.net's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

Source: web.dev

69% of mosaic02.ztat.net's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

Source: web.dev

How third-party costs are calculated

All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.

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