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https://www.zalando.com

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
69
GRADE
D
FIX
4
REVIEW
3
PASS
5
INFO
2

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

Mobile Desktop
79
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
92
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.

1.16 s

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

2.22 s

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

139 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.

2.29 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.

3.70 s

Page Load Progression

669 ms
1.3 s
2.0 s
2.7 s
3.3 s
4.0 s
4.7 s
5.3 s
Checks
14
5 PASS 3 REVIEW 4 FIX
F
Page Weight Budget
Action
2.9 MB transferred, 109 requests
FIX
2.9 MB transferred, 109 requests
Warning::
Page weighs 8.4 MB (2.9 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::
109 HTTP requests — consider bundling or reducing
Each request adds latency. Bundle small files, use sprites, or eliminate unnecessary requests.
Info::
Estimated 0.61 g CO2 per page load
2.9 MB / 2.4 MB budget
2.9 MB transferred
109 requests
0.61 g CO2 per page load
JavaScript 1.8 MiB 61%
Images 702.1 KiB 23%
Fonts 203.3 KiB 7%
Other 108.0 KiB 4%
HTML 105.5 KiB 4%
CSS 48.7 KiB 2%
Other 3.4 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 (2.9 MiB of 2.9 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Bundles
Action
44 scripts, 745 KB unused
FIX
44 scripts, 745 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...: 117 KB unused (70%)
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://mosaic01.ztat.net/pnl/gtag/js?id=G-MDW1S9P...: 67 KB unused (39%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=AW-100...: 65 KB unused (45%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 745 KB
745 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 KB117 KB (70%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-T3W9FX&l=dataLayer150 KB74 KB (50%)✓3rd
https://mosaic01.ztat.net/pnl/gtag/js?id=G-MDW1S9PQPW&l=dataLayerGA4170 KB67 KB (39%)✓3rd
https://www.googletagmanager.com/gtag/js?id=AW-1006368194&cx=c&gtm=4e6490h2144 KB65 KB (45%)✓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 KB49 KB (32%)✓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=71de8fe5-9797-7fbf-0442-3708ad570210158 KB31 KB (20%)✓3rd
https://app.usercentrics.eu/browser-ui/3.97.0/VirtualServiceItem-39329dba.js49 KB27 KB (55%)✓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
24 images, 0 KB saveable
REVIEW
24 images, 0 KB saveable
Warning::
https://mosaic02.ztat.net/rnd/ng/app-qr-code/app-q... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
24 images 702 KB
0 oversized -0 KB
16 legacy format
1 missing dimensions CLS risk

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

C
JS Execution Cost
Action
1702ms total JS execution
REVIEW
1702ms total JS execution
Warning::
https://mosaic01.ztat.net/base-assets/9-1-0/requir...: 289ms CPU time
Warning::
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/SQOS...: 286ms CPU time
Warning::
Unattributable: 262ms CPU time
Info::
https://www.zalando.es/: 221ms CPU time
Info::
https://mosaic01.ztat.net/base-assets/9-1-0/assets...: 212ms CPU time
Warning::
Third-party scripts: 1702ms (100% of total)

Main Thread Breakdown

Script Evaluation 68% Other 14% Script Parsing & Compilation 7% Style & Layout 5% Rendering 3%
ScriptTotalScriptingParse/CompileParty
https://mosaic01.ztat.net/base-assets/9-1-0/require-2.1.22.min.js289ms282ms1ms3rd
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/SQOSfQaLYL/ejJ9ETIaAwk/ASh/6HHE5dF9v?v=71de8fe5-9797-7fbf-0442-3708ad570210286ms266ms9ms3rd
Unattributable262ms75ms0ms3rd
https://www.zalando.es/221ms8ms13ms3rd
https://mosaic01.ztat.net/base-assets/9-1-0/assets/bundle.js212ms177ms5ms3rd
https://www.zalando.es/s0vn5AnFqa/9w8BYeCp/Cc/JiOSfQ8rYLbtbrmi/IntzETIaAwk/L1Q/vSStVYQkC191ms170ms11ms3rd
https://mosaic01.ztat.net/pnl/gtag/js?id=G-MDW1S9PQPW&l=dataLayerGA491ms78ms12ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-T3W9FX&l=dataLayer85ms72ms11ms3rd
https://app.usercentrics.eu/browser-ui/3.97.0/index.module.js65ms57ms0ms3rd
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 500 ms 1.0 s 1.5 s 2.0 s FCP 1.2 s LCP 2.2 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 — 58.3 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
109 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 1702ms · 791KB · $23/mo
mosaic01.ztat.net
Other
Costly
Execution 289ms
Transfer 8 KB
Monthly Cost $4/mo
www.zalando.es
Other
Costly
Execution 286ms
Transfer 158 KB
Unused 20%
Monthly Cost $4/mo
Unattributable
Other
Costly
Execution 262ms
Transfer 0 KB
Monthly Cost $3/mo
www.zalando.es
Other
Costly
Execution 221ms
Transfer 103 KB
Monthly Cost $3/mo
mosaic01.ztat.net
Other
Costly
Execution 212ms
Transfer 80 KB
Unused 30%
Monthly Cost $3/mo
www.zalando.es
Other
Optional
Execution 191ms
Transfer 1 KB
Unused 21%
Monthly Cost $3/mo
mosaic01.ztat.net
Other
Optional
Execution 91ms
Transfer 170 KB
Unused 39%
Monthly Cost $1/mo
Google Tag Manager
Tag Manager
Optional
Execution 85ms
Transfer 150 KB
Unused 50%
Monthly Cost $1/mo
app.usercentrics.eu
Other
Optional
Execution 65ms
Transfer 120 KB
Unused 45%
Monthly Cost $1/mo

These scripts may cost more than they're worth

  • mosaic01.ztat.net adds 289ms and costs ~$4/month
  • www.zalando.es adds 286ms and costs ~$4/month
  • Unattributable adds 262ms and costs ~$3/month
  • www.zalando.es adds 221ms and costs ~$3/month
  • mosaic01.ztat.net adds 212ms and costs ~$3/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 289ms 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 286ms 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 262ms 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 221ms 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 212ms 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

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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