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
1.5 MB transferred, 62 requests
REVIEW
1.5 MB transferred, 62 requests
Info::
i
Page weighs 3.7 MB (1.5 MB transferred)
Warning::
!
JavaScript is 874 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 874 KB
Info::
i
Fonts are 342 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 342 KB
Info::
i
62 HTTP requests
Info::
i
Estimated 0.31 g CO2 per page load
1.5 MBtransferred
62 requests
0.31 g CO2 per page load
JavaScript874.2 KiB58%
Fonts341.9 KiB23%
Images169.6 KiB11%
CSS70.4 KiB5%
Other27.7 KiB2%
HTML11.9 KiB1%
Other5.1 KiB0%
Other3.4 KiB0%
Other614 B0%
Other540 B0%
02.4 MB4.9 MB
Approaching limit
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
C
Image Optimization
Action
16 images, 0 KB saveable
REVIEW
16 images, 0 KB saveable
Warning::
!
https://www.viber.com/app/themes/viber/assets/imag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.viber.com/app/themes/viber/assets/imag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
!
https://www.viber.com/ is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
16images170 KB
0oversized-0 KB
15legacy format
3missing 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
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
6 fonts (342 KB)
PASS
6 fonts (342 KB)
Info::
i
6 font(s) use font-display: swap (FOUT risk but functional)
Web fonts
6
342 KB total
Render-blocking
0
of 6
Dominant font-display
swap
Most common across fonts
Font loading timeline
TransferFOIT (block)FOUT (swap)
Roboto-Light.woff2woff2swap
Size63 KB
Load time20 ms
Start1.1 s
RiskFOUT — text flashes from fallback to web font
Roboto-Thin.woff2woff2swap
Size62 KB
Load time23 ms
Start1.1 s
RiskFOUT — text flashes from fallback to web font
fa-solid-900.woff2woff2swap
Size38 KB
Load time24 ms
Start1.1 s
RiskFOUT — text flashes from fallback to web font
fa-brands-400.woff2woff2swap
Size54 KB
Load time24 ms
Start1.1 s
RiskFOUT — text flashes from fallback to web font
Roboto-Regular.woff2woff2swap
Size63 KB
Load time27 ms
Start1.1 s
RiskFOUT — text flashes from fallback to web font
Roboto-Bold.woff2woff2swap
Size62 KB
Load time33 ms
Start1.1 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
2 hints, 0 missing preconnects
PASS
2 hints, 0 missing preconnects
Info::
✓
Page uses 2 resource hint(s)
Current Resource Hints
preconnect—
preload—
dns-prefetch
2
prefetch—
2 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
62 requests over 1804ms
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-party3282ms · 877KB · $44/mo
Script
Category
Execution
Transfer
Unused
Monthly Cost
Verdict
www.viber.com
www.viber.com
Other
818ms
52 KB
—
$11/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
435ms
166 KB
41%
$6/mo
Costly
Unattributable
Unattributable
Other
400ms
0 KB
—
$5/mo
Costly
OneTrust
cdn.cookielaw.org
Consent
378ms
84 KB
42%
$5/mo
Essential
Google Tag Manager
www.googletagmanager.com
Tag Manager
355ms
161 KB
41%
$5/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
346ms
154 KB
53%
$5/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
274ms
134 KB
44%
$4/mo
Costly
s.go-mpulse.net
s.go-mpulse.net
Other
126ms
58 KB
66%
$2/mo
Optional
www.viber.com
www.viber.com
Other
78ms
36 KB
69%
$1/mo
Optional
Mixpanel
cdn.mxpnl.com
Analytics
73ms
32 KB
—
$1/mo
Optional
www.viber.com
Other
Costly
Execution818ms
Transfer52 KB
Monthly Cost$11/mo
Google Tag Manager
Tag Manager
Costly
Execution435ms
Transfer166 KB
Unused41%
Monthly Cost$6/mo
Unattributable
Other
Costly
Execution400ms
Transfer0 KB
Monthly Cost$5/mo
OneTrust
Consent
Essential
Execution378ms
Transfer84 KB
Unused42%
Monthly Cost$5/mo
Google Tag Manager
Tag Manager
Costly
Execution355ms
Transfer161 KB
Unused41%
Monthly Cost$5/mo
Google Tag Manager
Tag Manager
Costly
Execution346ms
Transfer154 KB
Unused53%
Monthly Cost$5/mo
Google Tag Manager
Tag Manager
Costly
Execution274ms
Transfer134 KB
Unused44%
Monthly Cost$4/mo
s.go-mpulse.net
Other
Optional
Execution126ms
Transfer58 KB
Unused66%
Monthly Cost$2/mo
www.viber.com
Other
Optional
Execution78ms
Transfer36 KB
Unused69%
Monthly Cost$1/mo
Mixpanel
Analytics
Optional
Execution73ms
Transfer32 KB
Monthly Cost$1/mo
These scripts may cost more than they're worth
www.viber.com adds 818ms and costs ~$11/month
Google Tag Manager adds 435ms and costs ~$6/month
Unattributable adds 400ms and costs ~$5/month
Google Tag Manager adds 355ms and costs ~$5/month
Google Tag Manager adds 346ms and costs ~$5/month
Google Tag Manager adds 274ms and costs ~$4/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.viber.com takes 818ms 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 435ms 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 400ms 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 355ms 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 346ms 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 Google Tag Manager'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 274ms 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
66% of s.go-mpulse.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 www.viber.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.