JavaScript snippets for measuring web performance in Chrome DevTools. Execute with mcpchrome-devtoolsevaluatescript, capture output with mcpchrome-devtoolsgetconsolemessage.
| Cumulative Layout Shift (CLS) | Quick check for Cumulative Layout Shift, a Core Web Vital that measures visual stability | scripts/CLS.js | | Interaction to Next Paint (INP) | Tracks Interaction to Next Paint, a Core Web Vital that measures responsiveness | scripts/INP.js |
| LCP Image Entropy | Checks if images qualify as LCP candidates based on their entropy (bits per pixel) | scripts/LCP-Image-Entropy.js | | LCP Sub-Parts | Breaks down Largest Contentful Paint into its four phases to identify optimization opportunities | scripts/LCP-Sub-Parts.js |
Intelligent Core Web Vitals analysis with automated workflows and decision trees. Measures LCP, CLS, INP with guided debugging that automatically determines follow-up analysis based on results. Includes workflows for LCP deep dive (5 phases), CLS investigation (loading vs interaction), INP debugging (latency breakdown + attribution), and cross-skill integration with loading, interaction, and media skills. Use when the user asks about Core Web Vitals, LCP optimization, layout shifts, or interaction responsiveness. Compatible with Chrome DevTools MCP. Source: nucliweb/webperf-snippets.