Intentional for dynamic content, but increases server load for every page view.
Got: no-cache, no-store, must-revalidate
Info::
i
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control
no-cache, no-store, must-revalidate
Directive
Value
Meaning
no-cache
—
Cache but always revalidate first
no-store
—
Never cache this response
must-revalidate
—
Must recheck with server after expiry
C
Page Weight Budget
Action
1.7 MB transferred, 49 requests
REVIEW
1.7 MB transferred, 49 requests
Info::
i
Page weighs 3.9 MB (1.7 MB transferred)
Warning::
!
JavaScript is 1.3 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 1.3 MB
Info::
✓
49 HTTP requests
Info::
i
Estimated 0.37 g CO2 per page load
1.7 MBtransferred
49 requests
0.37 g CO2 per page load
JavaScript1.3 MiB74%
Images249.1 KiB14%
Fonts101.4 KiB6%
CSS58.7 KiB3%
HTML39.4 KiB2%
Other14.8 KiB1%
Other1.3 KiB0%
Other618 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
B
Third-Party Impact
53% third-party, 0 ms blocking
REVIEW
53% third-party, 0 ms blocking
Warning::
!
Third-party code accounts for 53% of page weight (946.2 KiB of 1.7 MiB)
Info::
✓
Third-party blocking time is low (0 ms)
47%
53%
First-party Third-party
B
Image Optimization
11 images, 0 KB saveable
REVIEW
11 images, 0 KB saveable
Warning::
!
is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
11images249 KB
0oversized-0 KB
10legacy format
1missing dimensionsCLS risk
Set explicit width and height to prevent CLS.
Why this matters
Performance issues directly impact user engagement and conversion rates.
B
HTTP/3 (QUIC)
HTTP/3 not advertised
REVIEW
HTTP/3 not advertised
Info::
i
HTTP/3 (QUIC) is not advertised
HTTP/3 isn't advertised via Alt-Svc and the worker didn't negotiate h3. HTTP/3 reduces handshake latency (1-RTT instead of 2-3 RTTs) and is more resilient on lossy connections. Most modern CDNs (Cloudflare, Fastly, AWS CloudFront, Google Cloud CDN) support HTTP/3 with a single config switch -- consider enabling for mobile-heavy workloads.
C
Compression Algorithm
Action
Main response uses legacy deflate; upgrade to brotli or gzip
REVIEW
Main response uses legacy deflate; upgrade to brotli or gzip
Info::
i
Main HTML response uses deflate (legacy; prefer brotli or gzip)
Raw deflate is rarely used today and not handled identically across browsers. Switch to brotli (best) or gzip (universal).
B
Server-Timing Observability
No Server-Timing header found
REVIEW
No Server-Timing header found
Info::
i
No Server-Timing header found
Server-Timing exposes backend timing breakdowns to browser DevTools (e.g., `db: 45ms; render: 120ms; cache: 2ms`). Useful for diagnosing slow pages without backend log access. Most modern frameworks (Next.js, Cloudflare Workers, Fastly) emit it automatically; absence on a managed platform usually means telemetry headers are stripped at the edge.
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
2 fonts (101 KB)
PASS
2 fonts (101 KB)
Info::
i
2 font(s) use font-display: swap (FOUT risk but functional)
Web fonts
2
101 KB total
Render-blocking
0
of 2
Dominant font-display
swap
Most common across fonts
Font loading timeline
TransferFOIT (block)FOUT (swap)
JTUSjIg1_i6t8kCHKm459Wl...woff2swap
Size35 KB
Load time38 ms
Start702 ms
RiskFOUT — text flashes from fallback to web font
JTUSjIg1_i6t8kCHKm459Wd...woff2swap
Size67 KB
Load time54 ms
Start702 ms
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
6 hints, 0 missing preconnects
PASS
6 hints, 0 missing preconnects
Info::
✓
Page uses 6 resource hint(s)
Current Resource Hints
preconnect—
preload
6
dns-prefetch—
prefetch—
6 resource hints configured
A+
LCP Image Preload
LCP preload audit not available
PASS
LCP preload audit not available
Info::
✓
LCP image preload audit not available for this scan
A+
Main HTML Cache-Control
Main HTML uses no-store -- correct for sensitive/dynamic content
PASS
Main HTML uses no-store -- correct for sensitive/dynamic content
Info::
✓
Main HTML uses no-store -- correct for sensitive/dynamic content
Got: no-cache, no-store, must-revalidate
A+
Server Response Intelligence
2 server-response signal(s) detected
PASS
2 server-response signal(s) detected
Info::
✓
`Vary` header declared: Accept-Encoding
The page declares a `Vary` header, telling downstream caches which request headers the response varies on. Critical for content-negotiated responses (compression, language, cookies, device class).
Info::
i
No `ETag` or `Last-Modified` -- conditional GET not supported
Without either header, browsers can't issue conditional GETs and refresh always re-downloads the full response body even when nothing changed. Add `ETag: "<hash>"` (or `Last-Modified: <date>`) on cacheable responses; the server returns 304 Not Modified when the client's cached copy is still valid, saving bandwidth.
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
JavaScript Blocking
1 JS blocking issue(s) detected
PASS
1 JS blocking issue(s) detected
Warning::
!
4 render-blocking <script src> tag(s) without async/defer
Each `<script src=...>` without `async`, `defer`, or `type="module"` blocks HTML parsing while the browser fetches and executes it. The block lasts the entire round-trip + execution time -- on slow networks this translates directly into LCP delay. Add `defer` (executes after parse, in source order) for scripts that interact with the DOM, or `async` (executes whenever ready) for analytics / independent scripts. Module scripts (`type="module"`) are deferred by default.
Each `<link rel="stylesheet">` without a non-blocking `media` attribute holds up the first paint. Browsers download all of them before painting any content. Consolidate into 1-2 critical-path stylesheets; defer non-critical CSS via `<link rel="stylesheet" media="print" onload="this.media='all'">` or via the loadCSS pattern; inline above-the-fold CSS in `<style>` to short-circuit the request entirely.
Network Waterfall
49 requests over 1317ms
INFO
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
33%of JavaScript execution is third-party
First-party Third-party1092ms · 843KB · Kč135/mo
Script
Category
Execution
Transfer
Unused
Monthly Cost
Verdict
Google Tag Manager
www.googletagmanager.com
Tag Manager
292ms
181 KB
40%
Kč36/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
265ms
167 KB
42%
Kč33/mo
Costly
Google Tag Manager
www.googletagmanager.com
Tag Manager
196ms
155 KB
44%
Kč24/mo
Optional
Google Tag Manager
www.googletagmanager.com
Tag Manager
140ms
146 KB
49%
Kč17/mo
Optional
c.seznam.cz
c.seznam.cz
Other
100ms
51 KB
60%
Kč12/mo
Optional
Google Tag Manager
www.googletagmanager.com
Tag Manager
99ms
143 KB
61%
Kč12/mo
Optional
Google Tag Manager
Tag Manager
Costly
Execution292ms
Transfer181 KB
Unused40%
Monthly CostKč36/mo
Google Tag Manager
Tag Manager
Costly
Execution265ms
Transfer167 KB
Unused42%
Monthly CostKč33/mo
Google Tag Manager
Tag Manager
Optional
Execution196ms
Transfer155 KB
Unused44%
Monthly CostKč24/mo
Google Tag Manager
Tag Manager
Optional
Execution140ms
Transfer146 KB
Unused49%
Monthly CostKč17/mo
c.seznam.cz
Other
Optional
Execution100ms
Transfer51 KB
Unused60%
Monthly CostKč12/mo
Google Tag Manager
Tag Manager
Optional
Execution99ms
Transfer143 KB
Unused61%
Monthly CostKč12/mo
These scripts may cost more than they're worth
Google Tag Manager adds 292ms and costs ~Kč36/month
Google Tag Manager adds 265ms and costs ~Kč33/month
Google Tag Manager takes 292ms 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 265ms 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
60% of c.seznam.cz'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
61% 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.