Core Web Vitals

Checked

addyosmani·vlatest·frontend·MIT

Analyzes webpage Core Web Vitals (LCP, FID, CLS) to identify performance bottlenecks and suggest optimization strategies.

Repository

Install on your platform

Showing Claude Code. One command installs this skill into any of the agents below.

Run this in your project

terminal

$ npx skills add addyosmani/web-quality-skills --skill core-web-vitals -a claude-code

Uses the open-source skills CLI and needs Node.js. Add -g to install it for your user instead of this project.

What we know about this skill

Publisher

addyosmani

Taken from the source listing. We haven't verified who controls this account.

Install target

Live repository

Not pinned. Installing fetches whatever the repository holds at the time you run the command.

No human has reviewed this code. The checks below are a static scan of the files at one commit — nobody has run this skill or judged whether it works. A skill runs with whatever access you give your agent, so read the source before you install it.

Automated safety checks

scanned 27 Sept 2026

This skill passed all 6 checks. We read its files at one commit and looked for the things that make a skill dangerous to run — not for whether it works.

Declares what it does: passed
SKILL.md parses and declares a name and a description.
SKILL.md exists, its frontmatter parses, and it declares a name and a description.
No undeclared network calls: passed
Makes no network calls.
Every host the skill dials — from its scripts, its config endpoints or the commands it tells the agent to run — is either well-known package and API infrastructure or declared in its own frontmatter. Links in documentation are not counted.
No obfuscated payloads: passed
No encoded or obfuscated payloads.
No base64, hex or compressed blob is decoded and then executed, and no encoded shell commands.
No credential access: passed
Reads no keys, tokens, keychains or credential files.
Neither the code nor the SKILL.md instructions read SSH keys, cloud credentials, keychains, token stores, browser cookie databases or dotfiles that hold secrets.
No pipe-to-shell installers: passed
No pipe-to-shell or download-and-run installers.
No `curl … | sh` pattern, in the code or in the instructions, that runs code fetched at run time.
Pinned to a commit: passed
Scanned addyosmani/web-quality-skills at afa8da9421.
The exact upstream commit SHA that was scanned is recorded, so the result refers to specific bytes.

Commit: afa8da9421
Manifest: skills/core-web-vitals/SKILL.md
Scanned: 4 files, 618 lines

This is a static scan, not a review. It reads the skill's files; it does not run them, and it cannot tell you whether the skill is any good or whether the code does what its description says. A skill runs with whatever access you give your agent.

What each check looks for →

About this skill

What it does

The core-web-vitals skill helps assess and optimize a website’s performance based on key metrics like Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). It provides actionable insights to improve user experience by identifying bottlenecks in loading speed, interactivity, and visual stability.

When to use it

You're optimizing a website for better search engine rankings.
You want to identify performance issues that affect user engagement.
You’re preparing a site for high traffic or critical business pages.
You need to ensure consistent layout rendering across different devices and screen sizes.

Key capabilities

Measures Largest Contentful Paint (LCP) for loading performance.
Tracks First Input Delay (FID) to evaluate interactivity responsiveness.
Monitors Cumulative Layout Shift (CLS) to detect unexpected layout changes.
Provides detailed reports with recommendations for improvement.

Example prompts

"Analyze the core web vitals of my website and provide a report."
"What are the main issues affecting my site's Largest Contentful Paint score?"
"How can I reduce Cumulative Layout Shift on this page?"

Tips & gotchas

Ensure your website is fully loaded before running the analysis for accurate results.
Use real user data or representative traffic patterns to get meaningful insights, as lab-based tests may not reflect actual performance.