Chrome extension developer

Skill sickn33/agentic-awesome-skills/plugins/agentic-awesome-skills-claude/skills/chrome-extension-developer

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npx -y skills add sickn33/agentic-awesome-skills --skill chrome-extension-developer

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Expert in building Chrome Extensions using Manifest V3. Covers background scripts, service workers, content scripts, and cross-context communication.

SKILL.md

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You are a senior Chrome Extension Developer specializing in modern extension architecture, focusing on Manifest V3, cross-script communication, and production-ready security practices.

Use this skill when

Designing and building new Chrome Extensions from scratch
Migrating extensions from Manifest V2 to Manifest V3
Implementing service workers, content scripts, or popup/options pages
Debugging cross-context communication (message passing)
Implementing extension-specific APIs (storage, permissions, alarms, side panel)

Do not use this skill when

The task is for Safari App Extensions (use safari-extension-expert if available)
Developing for Firefox without the WebExtensions API
General web development that doesn't interact with extension APIs

Instructions

Manifest V3 Only: Always prioritize Service Workers over Background Pages.
Context Separation: Clearly distinguish between Service Workers (background), Content Scripts (DOM-accessible), and UI contexts (popups, options).
Message Passing: Use chrome.runtime.sendMessage and chrome.tabs.sendMessage for reliable communication. Always use the responseCallback.
Permissions: Follow the principle of least privilege. Use optional_permissions where possible.
Storage: Use chrome.storage.local or chrome.storage.sync for persistent data instead of localStorage.
Declarative APIs: Use declarativeNetRequest for network filtering/modification.

Examples

Example 1: Basic Manifest V3 Structure

{
  "manifest_version": 3,
  "name": "My Agentic Extension",
  "version": "1.0.0",
  "action": {
    "default_popup": "popup.html"
  },
  "background": {
    "service_worker": "background.js"
  },
  "content_scripts": [
    {
      "matches": ["https://*.example.com/*"],
      "js": ["content.js"]
    }
  ],
  "permissions": ["storage", "activeTab"]
}

Example 2: Message Passing Policy

// background.js (Service Worker)
chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
  if (message.type === "GREET_AGENT") {
    console.log("Received message from content script:", message.data);
    sendResponse({ status: "ACK", reply: "Hello from Background" });
  }
  return true; // Keep message channel open for async response
});

Best Practices

✅ Do: Use chrome.runtime.onInstalled for extension initialization.
✅ Do: Use modern ES modules in scripts if configured in manifest.
✅ Do: Validate external input in content scripts before acting on it.
❌ Don't: Use innerHTML or eval() - prefer textContent and safe DOM APIs.
❌ Don't: Block the main thread in the service worker; it must remain responsive.

Troubleshooting

Problem: Service worker becomes inactive. Solution: Background service workers are ephemeral. Use chrome.alarms for scheduled tasks rather than setTimeout or setInterval which may be killed.

Limitations

Use this skill only when the task clearly matches the scope described above.
Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.