Perflex

Real-time JavaScript performance profiling with function-level attribution and AI-powered remediation

Perflex tells you exactly which line of JavaScript is making your site slow — and how to fix it. It passively instruments any page you visit and attributes main-thread time down to the originating script, function, and source position. It pattern-matches your session against 30+ known performance anti-patterns and generates concrete remediation plans with before/after code, a risk level, and a note on why the fix is safe for your UI and business logic. FEATURES • Function-level attribution via the Long Animation Frames API • Script leaderboard ranked by main-thread time, long tasks, transfer size & more • Live Core Web Vitals (LCP, INP, CLS), TBT, FPS, JS heap, and a 0–100 health score • Zoomable interaction timeline with causal chains (click → task → fetch → reflow → shift ) • 30+ anti-pattern detectors across loading, execution, rendering, network, third-party & frameworks • Framework-aware: detects React/Vue/Angular/Next/Nuxt and flags dev builds shipped to production • Business-safe remediations with before/after code and risk levels • Optional AI remediation using your own Anthropic Claude API key • In-page overlay (Ctrl+Shift+X) with live FPS / heap / long tasks • Export to JSON, HAR, OpenTelemetry traces, and PDF; shareable session links PRIVACY Everything runs locally in your browser. No account, no tracking, nothing is uploaded. The optional AI feature sends only an anonymized, PII-free summary to Anthropic — and only when you click "AI Analysis" with your own API key configured. Perflex is free and open source (MIT). Source: https://github.com/svemulapati/perflex