Skills

performance

performance is a skill in addyosmani/web-quality-skills, last changed 24 Aug 2026. It can reach the network and name web addresses. Our pattern check flagged nothing at commit afa8da9 on 27 Oct 2026.

Pattern check: nothing flagged · commit afa8da9 · 27 Oct 2026

Install
From the author
Optimize web performance for faster loading and better user experience. Use when asked to "speed up my site", "optimize performance", "reduce load time", "fix slow loading", "improve page speed", or "performance audit".
Licence
MIT
Repo stars
3.0k
Folder last changed
24 Aug 2026 (opens in a new tab)
Publisher
addyosmani
Files
3 files
Checked
afa8da9 (opens in a new tab) · 27 Oct 2026

Install

Each tab says whether it installs commit afa8da9, the one we checked, or the latest version.

No tab for your agent? Use Any agent for OpenCode, Goose, Windsurf (Devin Desktop), Zed, Roo Code, Factory Droid, Junie, Amp and Antigravity, and Claude Code for Cline. Kiro needs the folder copied by hand.

Pinned to commit afa8da9, the one we checked.

From your project's root folder:

tmp="$(mktemp -d)" &&
  git clone -q --depth 1 --filter=blob:none --no-checkout https://github.com/addyosmani/web-quality-skills.git "$tmp" &&
  git -C "$tmp" fetch -q --depth 1 origin afa8da942115f2961fdbfa80807ea0b232ff6c00 &&
  git -C "$tmp" sparse-checkout set -- skills/performance &&
  git -C "$tmp" checkout -q afa8da942115f2961fdbfa80807ea0b232ff6c00 &&
  mkdir -p .claude/skills &&
  mkdir .claude/skills/performance &&
  cp -R "$tmp"/skills/performance/. .claude/skills/performance/ &&
  rm -rf "$tmp"

If Claude Code was already running and this created the skills folder, run /reload-skills.

Or install the web-quality-skills plugin it ships in. Installs the latest version, not the one we checked. Installs everything in the plugin, including any hooks, MCP servers and scripts our check doesn't cover.

claude plugin marketplace add addyosmani/web-quality-skills --scope project &&
  claude plugin install web-quality-skills@addy-web-quality-skills --scope project
Claude Code docs (opens in a new tab)

What it can touch

From the files and frontmatter at commit afa8da9. This is how much a skill can do, not whether it is risky.

What it can touch: Scripts or outside hosts

  • Reaches the network

    It sends or fetches data over the internet, for example with curl, an HTTP library or a package install.

  • Names web addresses

    It mentions outside web addresses the agent may visit. We list them but don't follow them.

Pattern check

Pattern check: nothing flagged · commit afa8da9 · 27 Oct 2026

We checked every text file in this skill, at commit afa8da9 on 27 Oct 2026, against 45 published patterns such as download-and-run commands, hidden text and credential access. We don't run the skill, we don't read the web pages it points to, and we can't judge everything its instructions might lead an agent to do. In published tests, pattern checks like this one missed most malicious skills. Read the skill before you install it — especially anything it asks you to download or run.

How the check worksReport an incorrect finding

Outside links we did not follow

  • https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Status/103
  • https://blog.cloudflare.com/early-hints-performance/
  • https://fonts.googleapis.com
  • https://developer.chrome.com/docs/web-platform/prerender-pages
  • https://developer.chrome.com/docs/web-platform/view-transitions
  • https://github.com/ChromeDevTools/chrome-devtools-mcp/blob/main/docs/tool-reference.md
  • https://developer.chrome.com/docs/crux/api
  • https://web.dev/articles/vitals-measurement-getting-started
  • https://developers.google.com/speed/docs/insights/v5/get-started
  • https://github.com/GoogleChrome/web-vitals
Show 2 more
  • https://web.dev/articles/vitals-field-measurement-best-practices
  • https://web.dev/articles/find-slow-interactions-in-the-field

Format check

Each agent reads SKILL.md a little differently. We check the file against each one's published rules; we don't run the skill in any agent.

  • Agent Skills specPasses with warnings

    The open format from agentskills.io, held to what the strictest agents enforce, so one folder loads everywhere.

    • Warning

      Paths that may not work once the skill is installed: line 78: ../core-web-vitals/SKILL.md#lcp-largest-contentful-paint (outside the skill folder) and line 399: ../core-web-vitals/SKILL.md (outside the skill folder). B6

      Fix: Use forward-slash paths relative to SKILL.md, and copy shared files into the skill.

    • Note

      Reference files over 100 lines with no table of contents at the top: references/MEASUREMENT.md (108 lines). B5

      Fix: Add a short list of the sections at the top of each.

  • Claude CodePasses with warnings

    Claude Code reads its own extra fields, ignores unknown ones, and still loads a skill whose frontmatter is broken, without its fields.

    • Warning

      Paths that may not work once the skill is installed: line 78: ../core-web-vitals/SKILL.md#lcp-largest-contentful-paint (outside the skill folder) and line 399: ../core-web-vitals/SKILL.md (outside the skill folder). B6

      Fix: Use forward-slash paths relative to SKILL.md, and copy shared files into the skill.

    • Note

      Reference files over 100 lines with no table of contents at the top: references/MEASUREMENT.md (108 lines). B5

      Fix: Add a short list of the sections at the top of each.

  • Claude apps & API uploadPasses with warnings

    Uploading to claude.ai or the Claude API, or packaging with Anthropic's script, accepts only the six spec fields and stops on anything else.

    • Warning

      Paths that may not work once the skill is installed: line 78: ../core-web-vitals/SKILL.md#lcp-largest-contentful-paint (outside the skill folder) and line 399: ../core-web-vitals/SKILL.md (outside the skill folder). B6

      Fix: Use forward-slash paths relative to SKILL.md, and copy shared files into the skill.

    • Note

      The description is 219 characters. The claude.ai Help Center says 200 at most, though Anthropic's API docs and validator allow 1,024. D4

      Fix: If the claude.ai upload refuses it, trim the description to 200 characters.

    • Note

      Reference files over 100 lines with no table of contents at the top: references/MEASUREMENT.md (108 lines). B5

      Fix: Add a short list of the sections at the top of each.

  • OpenAI (Codex & API)Passes with warnings

    Codex finds SKILL.md by its exact name and needs a description; OpenAI's Skills API checks the frontmatter against the spec and caps uploads.

    • Warning

      Paths that may not work once the skill is installed: line 78: ../core-web-vitals/SKILL.md#lcp-largest-contentful-paint (outside the skill folder) and line 399: ../core-web-vitals/SKILL.md (outside the skill folder). B6

      Fix: Use forward-slash paths relative to SKILL.md, and copy shared files into the skill.

  • VS Code & CopilotPasses with warnings

    VS Code reads skills one folder below .github/skills, .claude/skills or .agents/skills and falls back to the folder name when the name is missing or differs; GitHub's Copilot docs require the exact name SKILL.md.

    • Warning

      Paths that may not work once the skill is installed: line 78: ../core-web-vitals/SKILL.md#lcp-largest-contentful-paint (outside the skill folder) and line 399: ../core-web-vitals/SKILL.md (outside the skill folder). B6

      Fix: Use forward-slash paths relative to SKILL.md, and copy shared files into the skill.

SKILL.md

Files

3 files

PathSize
SKILL.md (opens in a new tab)13.5 KB
references/MEASUREMENT.md (opens in a new tab)7.2 KB
references/RUM.md (opens in a new tab)3.1 KB

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