Webperf Core Web Vitals

This is a diagnostic powerhouse for Core Web Vitals. It doesn't just measure LCP, CLS, and INP, it actually walks you through what to do next based on the results. If LCP is over 2.5s, it automatically suggests running subparts analysis. If you've got layout shifts, it knows to check lazy-loaded images and font swaps. The decision trees are the real value here: run one script, get a specific next step based on thresholds. It's built for Chrome DevTools MCP and integrates with companion skills for loading, interaction, and media when you need to dig deeper. From Joan Leon's webperf-snippets collection, so the scripts themselves are battle-tested in production debugging.

skills.sh installs: 295
GitHub stars: 1.5K
last updated: Aug 21, 2026

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Install

$ npx -y skills add nucliweb/webperf-snippets --skill webperf-core-web-vitals --agent claude-code

Installs into .claude/skills of the current project.

Files

WebPerf: Core Web Vitals

JavaScript snippets for measuring web performance in Chrome DevTools.

Running a script

Run the script with mcp__chrome-devtools__evaluate_script, passing the file instead of its code: sourcePath with the absolute path of scripts/<Name>.js in this skill, and format: "script", since a script runs by itself and is not a function. Read the object it returns. The scripts have no console output, so the returned object is the result: script, status and the metric data (value, rating, details, items, issues), as described in references/schema.md.
When status is "tracking", the script keeps observing the page. After the interactions, call the function named in getDataFn with another mcp__chrome-devtools__evaluate_script call, as an arrow function in function, for example () => getINP(), and read the object it returns.
When status is "error" or "unsupported", read error: the page may not have loaded yet, or the browser lacks the API.