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.
C
Image Optimization
Action
19 images, 0 KB saveable
REVIEW
19 images, 0 KB saveable
Warning::
!
https://www.thelancet.com/do/10.1016/4f9d9162-93c9... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/templates/jsp/_style2/_m... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/pb-assets/Lancet/homepag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/do/10.1016/04f8c4ae-ce4a... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/do/10.1016/2e3f8d55-c132... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/pb-assets/Lancet/homepag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/pb-assets/Lancet/homepag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/pb-assets/ux3/logos/lanc... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/pb-assets/Lancet/homepag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.thelancet.com/do/10.1016/a7d423f9-578d... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
19images625 KB
0oversized-0 KB
13legacy format
10missing 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
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
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
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
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
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
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
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
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
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
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
16 fonts (501 KB)
PASS
16 fonts (501 KB)
Info::
i
16 font(s) use font-display: swap (FOUT risk but functional)
Web fonts
16
501 KB total
Render-blocking
0
of 16
Dominant font-display
swap
Most common across fonts
Font loading timeline
TransferFOIT (block)FOUT (swap)
icomoon-c58c472f6dbb45c...woffswap
Size42 KB
Load time48 ms
Start1.4 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
source-sans-pro-latin-9...woff2swap
Size1 KB
Load time21 ms
Start1.6 s
RiskFOUT — text flashes from fallback to web font
icomoon-d4d19ebe45b4314...ttfswap
Size32 KB
Load time41 ms
Start1.9 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansWebPro-Italic-...woff2swap
Size79 KB
Load time26 ms
Start2.1 s
RiskFOUT — text flashes from fallback to web font
NexusSansOffcPro-Italic...ttfswap
Size61 KB
Load time32 ms
Start2.3 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
6xK3dSBYKcSV-LCoeQqfX1R...woff2swap
Size15 KB
Load time18 ms
Start2.5 s
RiskFOUT — text flashes from fallback to web font
2D333F_2_0.woff2woff2swap
Size1 KB
Load time214 ms
Start2.7 s
RiskFOUT — text flashes from fallback to web font
2D333F_1_0.woff2woff2swap
Size1 KB
Load time719 ms
Start2.7 s
RiskFOUT — text flashes from fallback to web font
2D333F_2_0.woffwoffswap
Size1 KB
Load time291 ms
Start2.9 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
2D333F_1_0.woffwoffswap
Size1 KB
Load time206 ms
Start3.5 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansWebPro-d1d294e...woff2swap
Size71 KB
Load time40 ms
Start3.7 s
RiskFOUT — text flashes from fallback to web font
elsevierwordmark-regula...woff2swap
Size6 KB
Load time31 ms
Start3.8 s
RiskFOUT — text flashes from fallback to web font
elsevierwordmark-regula...ttfswap
Size5 KB
Load time22 ms
Start3.8 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansOffcPro-35ae39...ttfswap
Size56 KB
Load time35 ms
Start3.9 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansWebPro-Bold-df...woff2swap
Size74 KB
Load time27 ms
Start4.0 s
RiskFOUT — text flashes from fallback to web font
NexusSansOffcPro-Bold-3...ttfswap
Size58 KB
Load time35 ms
Start4.0 s
RiskFOUT — text flashes from fallback to web font
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 ~76 KB and ~152 ms
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
A+
Green Hosting
Whether the site is served from green-energy infrastructure
PASS
Green Hosting
This site is hosted on green energy infrastructure
Provider: Cloudflare
Network Waterfall
114 requests over 7873ms
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-party2443ms · 731KB · $32/mo
Script
Category
Execution
Transfer
Unused
Monthly Cost
Verdict
www.thelancet.com
www.thelancet.com
Other
1124ms
56 KB
—
$15/mo
Costly
Unattributable
Unattributable
Other
312ms
0 KB
—
$4/mo
Costly
securepubads.g.doubleclick.net
securepubads.g.doubleclick.net
Other
307ms
188 KB
53%
$4/mo
Costly
www.thelancet.com
www.thelancet.com
Other
233ms
217 KB
69%
$3/mo
Costly
pagead2.googlesyndication.com
pagead2.googlesyndication.com
Other
132ms
73 KB
42%
$2/mo
Optional
www.thelancet.com
www.thelancet.com
Other
117ms
0 KB
—
$2/mo
Optional
OneTrust
cdn.cookielaw.org
Consent
110ms
119 KB
52%
$1/mo
Essential
www.thelancet.com
www.thelancet.com
Other
58ms
10 KB
—
$1/mo
Optional
www.thelancet.com
www.thelancet.com
Other
50ms
68 KB
76%
$1/mo
Optional
www.thelancet.com
Other
Costly
Execution1124ms
Transfer56 KB
Monthly Cost$15/mo
Unattributable
Other
Costly
Execution312ms
Transfer0 KB
Monthly Cost$4/mo
securepubads.g.doubleclick.net
Other
Costly
Execution307ms
Transfer188 KB
Unused53%
Monthly Cost$4/mo
www.thelancet.com
Other
Costly
Execution233ms
Transfer217 KB
Unused69%
Monthly Cost$3/mo
pagead2.googlesyndication.com
Other
Optional
Execution132ms
Transfer73 KB
Unused42%
Monthly Cost$2/mo
www.thelancet.com
Other
Optional
Execution117ms
Transfer0 KB
Monthly Cost$2/mo
OneTrust
Consent
Essential
Execution110ms
Transfer119 KB
Unused52%
Monthly Cost$1/mo
www.thelancet.com
Other
Optional
Execution58ms
Transfer10 KB
Monthly Cost$1/mo
www.thelancet.com
Other
Optional
Execution50ms
Transfer68 KB
Unused76%
Monthly Cost$1/mo
These scripts may cost more than they're worth
www.thelancet.com adds 1124ms and costs ~$15/month
Unattributable adds 312ms and costs ~$4/month
securepubads.g.doubleclick.net adds 307ms and costs ~$4/month
www.thelancet.com adds 233ms 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
www.thelancet.com takes 1124ms 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 312ms 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
securepubads.g.doubleclick.net takes 307ms 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
53% of securepubads.g.doubleclick.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
www.thelancet.com takes 233ms 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
69% of www.thelancet.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
52% of OneTrust'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
76% of www.thelancet.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.