Chrome's render-blocking label only flags synchronous parser-blocking resources in the head, missing many requests that actually delay FCP and LCP — like deferred scripts that gate SPA data fetches, code-split chunks, and the LCP image itself. DebugBear's Website Bottleneck Finder addresses this by replaying page loads with cached responses, delaying one resource at a time by 2 seconds, and flagging any resource that pushes FCP/LCP back by half the delay or more. A real-world example on virginatlantic.com shows how the tool identified which of 23 deferred JS scripts was impacting LCP, and preloading it yielded a 25%+ LCP improvement. The tool is free to use and can be paired with full Lighthouse analysis or continuous monitoring.
Table of contents
What is the Website Bottleneck Finder? The problem: Chrome's "render-blocking" label is too narrow How the tool works What can you do with the analysis result? A Real-life Example Go beyond one-off performance checks Monitor Page Speed & Core Web Vitals413 Impressions