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/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/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/pb-assets/Lancet/homepag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
19images560 KB
0oversized-0 KB
13legacy format
6missing 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
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 (499 KB)
PASS
16 fonts (499 KB)
Info::
i
16 font(s) use font-display: swap (FOUT risk but functional)
Web fonts
16
499 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 time58 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 time25 ms
Start1.6 s
RiskFOUT — text flashes from fallback to web font
icomoon-d4d19ebe45b4314...ttfswap
Size32 KB
Load time34 ms
Start1.8 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansWebPro-Italic-...woff2swap
Size79 KB
Load time34 ms
Start2.0 s
RiskFOUT — text flashes from fallback to web font
NexusSansOffcPro-Italic...ttfswap
Size60 KB
Load time36 ms
Start2.0 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
6xK3dSBYKcSV-LCoeQqfX1R...woff2swap
Size15 KB
Load time6 ms
Start2.4 s
RiskFOUT — text flashes from fallback to web font
2D333F_2_0.woff2woff2swap
Size1 KB
Load time173 ms
Start3.1 s
RiskFOUT — text flashes from fallback to web font
2D333F_1_0.woff2woff2swap
Size1 KB
Load time206 ms
Start3.1 s
RiskFOUT — text flashes from fallback to web font
2D333F_2_0.woffwoffswap
Size1 KB
Load time212 ms
Start3.3 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
2D333F_1_0.woffwoffswap
Size1 KB
Load time204 ms
Start3.3 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansWebPro-d1d294e...woff2swap
Size70 KB
Load time37 ms
Start3.6 s
RiskFOUT — text flashes from fallback to web font
elsevierwordmark-regula...woff2swap
Size5 KB
Load time24 ms
Start3.6 s
RiskFOUT — text flashes from fallback to web font
elsevierwordmark-regula...ttfswap
Size5 KB
Load time31 ms
Start3.7 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansOffcPro-35ae39...ttfswap
Size56 KB
Load time30 ms
Start3.7 s
RiskFOUT — text flashes from fallback to web font
Convert to woff2 for ~30% smaller file size
NexusSansWebPro-Bold-df...woff2swap
Size74 KB
Load time24 ms
Start3.8 s
RiskFOUT — text flashes from fallback to web font
NexusSansOffcPro-Bold-3...ttfswap
Size58 KB
Load time25 ms
Start3.8 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+
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
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 7720ms
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-party10786ms · 996KB · $143/mo
Script
Category
Execution
Transfer
Unused
Monthly Cost
Verdict
www.thelancet.com
www.thelancet.com
Other
4044ms
56 KB
—
$54/mo
Costly
Unattributable
Unattributable
Other
1356ms
0 KB
—
$18/mo
Costly
securepubads.g.doubleclick.net
securepubads.g.doubleclick.net
Other
1120ms
188 KB
54%
$15/mo
Costly
www.thelancet.com
www.thelancet.com
Other
1040ms
218 KB
69%
$14/mo
Costly
pagead2.googlesyndication.com
pagead2.googlesyndication.com
Other
584ms
73 KB
43%
$8/mo
Costly
OneTrust
cdn.cookielaw.org
Consent
479ms
119 KB
52%
$6/mo
Essential
Google Tag Manager
www.googletagmanager.com
Tag Manager
454ms
141 KB
41%
$6/mo
Costly
www.thelancet.com
www.thelancet.com
Other
434ms
1 KB
—
$6/mo
Costly
securepubads.g.doubleclick.net
securepubads.g.doubleclick.net
Other
255ms
34 KB
—
$3/mo
Costly
www.thelancet.com
www.thelancet.com
Other
211ms
68 KB
76%
$3/mo
Costly
www.thelancet.com
www.thelancet.com
Other
183ms
7 KB
—
$2/mo
Optional
www.thelancet.com
www.thelancet.com
Other
106ms
3 KB
—
$1/mo
Optional
www.thelancet.com
www.thelancet.com
Other
100ms
26 KB
—
$1/mo
Optional
www.thelancet.com
www.thelancet.com
Other
82ms
30 KB
—
$1/mo
Optional
static.cloudflareinsights.com
static.cloudflareinsights.com
Other
75ms
0 KB
—
$1/mo
Optional
OneTrust
cdn.cookielaw.org
Consent
73ms
9 KB
—
$1/mo
Essential
js-agent.newrelic.com
js-agent.newrelic.com
Other
72ms
14 KB
—
$1/mo
Optional
ep2.adtrafficquality.google
ep2.adtrafficquality.google
Other
65ms
8 KB
—
$1/mo
Optional
bam.nr-data.net
bam.nr-data.net
Other
53ms
1 KB
—
$1/mo
Optional
www.thelancet.com
Other
Costly
Execution4044ms
Transfer56 KB
Monthly Cost$54/mo
Unattributable
Other
Costly
Execution1356ms
Transfer0 KB
Monthly Cost$18/mo
securepubads.g.doubleclick.net
Other
Costly
Execution1120ms
Transfer188 KB
Unused54%
Monthly Cost$15/mo
www.thelancet.com
Other
Costly
Execution1040ms
Transfer218 KB
Unused69%
Monthly Cost$14/mo
pagead2.googlesyndication.com
Other
Costly
Execution584ms
Transfer73 KB
Unused43%
Monthly Cost$8/mo
OneTrust
Consent
Essential
Execution479ms
Transfer119 KB
Unused52%
Monthly Cost$6/mo
Google Tag Manager
Tag Manager
Costly
Execution454ms
Transfer141 KB
Unused41%
Monthly Cost$6/mo
www.thelancet.com
Other
Costly
Execution434ms
Transfer1 KB
Monthly Cost$6/mo
securepubads.g.doubleclick.net
Other
Costly
Execution255ms
Transfer34 KB
Monthly Cost$3/mo
www.thelancet.com
Other
Costly
Execution211ms
Transfer68 KB
Unused76%
Monthly Cost$3/mo
www.thelancet.com
Other
Optional
Execution183ms
Transfer7 KB
Monthly Cost$2/mo
www.thelancet.com
Other
Optional
Execution106ms
Transfer3 KB
Monthly Cost$1/mo
www.thelancet.com
Other
Optional
Execution100ms
Transfer26 KB
Monthly Cost$1/mo
www.thelancet.com
Other
Optional
Execution82ms
Transfer30 KB
Monthly Cost$1/mo
static.cloudflareinsights.com
Other
Optional
Execution75ms
Transfer0 KB
Monthly Cost$1/mo
OneTrust
Consent
Essential
Execution73ms
Transfer9 KB
Monthly Cost$1/mo
js-agent.newrelic.com
Other
Optional
Execution72ms
Transfer14 KB
Monthly Cost$1/mo
ep2.adtrafficquality.google
Other
Optional
Execution65ms
Transfer8 KB
Monthly Cost$1/mo
bam.nr-data.net
Other
Optional
Execution53ms
Transfer1 KB
Monthly Cost$1/mo
These scripts may cost more than they're worth
www.thelancet.com adds 4044ms and costs ~$54/month
Unattributable adds 1356ms and costs ~$18/month
securepubads.g.doubleclick.net adds 1120ms and costs ~$15/month
www.thelancet.com adds 1040ms and costs ~$14/month
pagead2.googlesyndication.com adds 584ms and costs ~$8/month
Google Tag Manager adds 454ms and costs ~$6/month
www.thelancet.com adds 434ms and costs ~$6/month
securepubads.g.doubleclick.net adds 255ms and costs ~$3/month
www.thelancet.com adds 211ms 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 4044ms 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 1356ms 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 1120ms 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
54% 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 1040ms 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
pagead2.googlesyndication.com takes 584ms 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
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
Google Tag Manager takes 454ms 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.thelancet.com takes 434ms 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 255ms 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.thelancet.com takes 211ms 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
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.