Core Web Vitals

Measure LCP, CLS, TTFB, and FCP with real browser performance APIs and grade them against web.dev thresholds. No signup required.

Prerequisites

• Playwright MCP (ships with Claude Code)

Trigger

• "Check Core Web Vitals for https://..."
• "Measure LCP on my landing page"
• "Is my CLS under 0.1?"
• "Why does my page feel slow to load?"

Workflow

1. mcp__playwright__browser_navigate to the URL, then wait ~3s so late layout shifts and the final LCP candidate land.
2. mcp__playwright__browser_evaluate with this function (returns a Promise — Playwright awaits it):