What PerfLens does
PerfLens is a real-session web performance observer built for developers, QA engineers, and performance enthusiasts. Unlike lab audit tools like Lighthouse or PageSpeed Insights that simulate empty loads under artificial throttling, PerfLens measures real timing data as you interact with live pages. It breaks down Core Web Vitals, flags long tasks, tracks layout shifts (CLS), measures network payload weight, and explains its findings in human-readable terms.
Key Features
- Real-Session Metrics — Captures live Core Web Vitals (LCP, INP, CLS), long task breakdowns, layout shifts, and total page resource weight.
- DevTools & Popup Views — Open a full-featured DevTools panel for granular performance analysis or click the extension popup for an instant score at a glance.
- Plain Language Diagnostics — Explains every performance bottleneck and metric in clear language, detailing step-by-step how your score was calculated.
- Stack & Framework Detection — Automatically detects the frontend framework and build setup of the target page to provide stack-tailored performance advice.
- 100% On-Device Privacy — Reads timing metrics locally within your browser session. Sends zero analytics, metrics, or telemetry to external servers.
Who it's for
Frontend engineers, web performance specialists, and QA teams who need real-world performance diagnostics during local development or production testing. It pairs well with API and network debugging tools like XHRScribe and CSS/state inspection with StyleSpy. Free on the Chrome Web Store; compatible with Chromium browsers.
FAQ
Does PerfLens collect or transmit my data? No. PerfLens operates 100% locally on your machine. All timing observation happens inside your browser, and no data is sent anywhere.
How does it differ from Lighthouse or synthetic tests? Synthetic tests run in isolated, throttled lab environments. PerfLens observes your actual browsing session with cached assets, real API responses, and live user interaction.
Where do I view the performance breakdown? You can inspect high-level scores directly in the extension popup or open the dedicated PerfLens panel inside Chrome DevTools for deep diagnostic insights.
Is it free? Yes, completely free on the Chrome Web Store.