Render-blocking resources
Flags resources SiteState identifies as blocking the rendering path during the current run.
Free render blocking resources test
Test render-blocking resources and find CSS or JavaScript delaying the first render.
Test a real page load and surface CSS, JavaScript and other resources SiteState classifies as render-blocking, LCP-critical, bandwidth-heavy or third-party.
Free · No signup required · Real Chromium lab test
What this tool measures
Critical-path evidence from the actual browser load
LCP-critical resources
Surfaces assets associated with the main-content rendering path and Largest Contentful Paint.
Bandwidth-heavy resources
Highlights large transfers that consume a disproportionate share of the page-load budget.
Third-party resources
Separates external resources so dependencies outside the first-party origin remain visible.
Transfer size
Shows resource weight alongside blocking classification so priority is based on both timing and cost.
Recommendation context
The SiteState report attaches reasons and remediation guidance to high-impact findings where available.
Interpret the result
Not every blocking resource should be removed — the goal is to shorten the critical path.
Stylesheets and synchronous scripts can be necessary for correct rendering, but unnecessary blocking work delays the first useful paint. The practical task is to distinguish truly critical resources from assets that can load later.
SiteState analyzes the browser load and ranks resource opportunities rather than treating every stylesheet or script as equally harmful.
Methodology
The classification comes from SiteState's controlled Chromium synthetic analysis of the current page load. It is broader than a static HTML-head parser because it uses observed browser resource behavior.
FAQ
Common questions about this speed test
How do I test render-blocking resources?
Run the SiteState render blocking resources test for the page URL. The Chromium load surfaces CSS, JavaScript and other resources classified as render-blocking, LCP-critical, bandwidth-heavy or third-party.
What are render-blocking resources?
Render-blocking resources are assets the browser must process before it can paint important page content. Stylesheets and synchronous scripts are common examples.
Does every stylesheet need to be removed from the critical path?
No. Some CSS is genuinely required for the first render. The goal is to keep critical CSS available while deferring or restructuring work that is not needed immediately.
Can JavaScript be render-blocking?
Yes. Synchronous JavaScript can delay parsing and rendering. SiteState also measures JavaScript CPU separately because scripts can remain expensive even after they stop blocking initial parsing.
Can SiteState monitor render-blocking changes over time?
SiteState's synthetic monitoring stores browser results and can detect broader performance regressions when page resources or scripts change.
Related free tools
Test another part of website speed
Total Blocking Time Test
Measure long-task main-thread blocking.
Open toolWebsite JavaScript Performance Test
Inspect script CPU and third-party impact.
Open toolLCP Test
See how the critical path affects main-content rendering.
Open toolPage Weight Test
Measure the total transfer and resource footprint.
Open toolContinuous performance
Need more than one test? Website performance monitoring keeps compatible browser metrics and regression history over time. Performance.
A one-off speed test is only a snapshot.
SiteState can keep the same website under continuous monitoring and detect when performance changes.