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
Page Weight Budget
1.3 MB transferred, 44 requests
REVIEW
1.3 MB transferred, 44 requests
Info::
✓
Page weighs 3.8 MB (1.3 MB transferred)
Warning::
!
JavaScript is 872 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 872 KB
Info::
✓
44 HTTP requests
Info::
i
Estimated 0.27 g CO2 per page load
1.3 MBtransferred
44 requests
0.27 g CO2 per page load
JavaScript872.2 KiB65%
Images216.6 KiB16%
Fonts114.0 KiB9%
CSS78.0 KiB6%
HTML32.6 KiB2%
Other14.3 KiB1%
Other7.7 KiB1%
Other726 B0%
02.4 MB4.9 MB
Under 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
B
Image Optimization
10 images, 0 KB saveable
REVIEW
10 images, 0 KB saveable
Warning::
!
https://media.nngroup.com/static/img/logos/amazon-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
10images217 KB
0oversized-0 KB
10legacy format
1missing dimensionsCLS 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
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 (114 KB)
PASS
3 fonts (114 KB)
Info::
i
3 font(s) use font-display: swap (FOUT risk but functional)
Web fonts
3
114 KB total
Render-blocking
0
of 3
Dominant font-display
swap
Most common across fonts
Font loading timeline
TransferFOIT (block)FOUT (swap)
SourceSansVariable.subs...woff2swap
Size24 KB
Load time9 ms
Start648 ms
RiskFOUT — text flashes from fallback to web font
Inter-VariableFont_opsz...woff2swap
Size69 KB
Load time5 ms
Start703 ms
RiskFOUT — text flashes from fallback to web font
SourceSansItalicVariabl...woff2swap
Size21 KB
Load time4 ms
Start1.3 s
RiskFOUT — 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
3 hints, 0 missing preconnects
PASS
3 hints, 0 missing preconnects
Info::
✓
Page uses 3 resource hint(s)
Current Resource Hints
preconnect
3
preload—
dns-prefetch—
prefetch—
3 resource hints configured
A+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
✓
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
Network Waterfall
44 requests over 1883ms
INFO
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
100%of JavaScript execution is third-party
First-party Third-party2933ms · 851KB · €16/mo
Script
Category
Execution
Transfer
Unused
Monthly Cost
Verdict
media.nngroup.com
media.nngroup.com
Other
752ms
159 KB
58%
€4/mo
Costly
www.nngroup.com
www.nngroup.com
Other
447ms
33 KB
—
€2/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
405ms
183 KB
33%
€2/mo
Costly
Unattributable
Unattributable
Other
366ms
0 KB
—
€2/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
251ms
173 KB
40%
€1/mo
Costly
cdn-cookieyes.com
cdn-cookieyes.com
Other
243ms
8 KB
—
€1/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
152ms
145 KB
45%
€1/mo
Optional
Facebook Pixel
connect.facebook.net
Advertising
124ms
44 KB
—
€1/mo
Optional
Facebook Pixel
connect.facebook.net
Advertising
122ms
97 KB
35%
€1/mo
Optional
cdn-cookieyes.com
cdn-cookieyes.com
Other
70ms
9 KB
—
€0/mo
Optional
media.nngroup.com
Other
Costly
Execution752ms
Transfer159 KB
Unused58%
Monthly Cost€4/mo
www.nngroup.com
Other
Costly
Execution447ms
Transfer33 KB
Monthly Cost€2/mo
Google Tag Manager
Tag Manager
Costly
Execution405ms
Transfer183 KB
Unused33%
Monthly Cost€2/mo
Unattributable
Other
Costly
Execution366ms
Transfer0 KB
Monthly Cost€2/mo
Google Tag Manager
Tag Manager
Costly
Execution251ms
Transfer173 KB
Unused40%
Monthly Cost€1/mo
cdn-cookieyes.com
Other
Costly
Execution243ms
Transfer8 KB
Monthly Cost€1/mo
Google Tag Manager
Tag Manager
Optional
Execution152ms
Transfer145 KB
Unused45%
Monthly Cost€1/mo
Facebook Pixel
Advertising
Optional
Execution124ms
Transfer44 KB
Monthly Cost€1/mo
Facebook Pixel
Advertising
Optional
Execution122ms
Transfer97 KB
Unused35%
Monthly Cost€1/mo
cdn-cookieyes.com
Other
Optional
Execution70ms
Transfer9 KB
Monthly Cost€0/mo
These scripts may cost more than they're worth
media.nngroup.com adds 752ms and costs ~€4/month
www.nngroup.com adds 447ms and costs ~€2/month
Google Tag Manager adds 405ms and costs ~€2/month
Unattributable adds 366ms and costs ~€2/month
Google Tag Manager adds 251ms and costs ~€1/month
cdn-cookieyes.com adds 243ms and costs ~€1/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
media.nngroup.com takes 752ms 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
58% of media.nngroup.com'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
www.nngroup.com takes 447ms 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 405ms 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 366ms 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 251ms 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
cdn-cookieyes.com takes 243ms 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.