# extensiondev/mcp [Health: Active]

**Category:** 💻 Developer Tools  
**Repository:** https://github.com/extensiondev/mcp  
**GitHub Stars:** 0  
**npm Downloads (last month):** 2667  
**Views:** 0  
**Installs:** 0  
**Upvotes:** 0  
**Directory Page:** https://allmcps.com/mcp/mcp-291

## Description
Build, run, inspect, and publish browser extensions from any MCP client. 28 tools, 11 browsers.

## Claude Desktop Quick Installation
Install path detected from listing signals. Uses `npx` (confidence: high):

```json
"mcpServers": {
  "mcp": {
    "command": "npx",
    "args": ["@extension.dev/mcp"]
  }
}
```

## Documentation

## What extensiondev/mcp does

extensiondev/mcp exposes browser-extension development operations through the Model Context Protocol. It is built on Extension.js and is intended for agents working with extensions on a developer’s machine. The server can create a project from a template, add common extension features, run the project, inspect runtime behavior, exercise the extension, and prepare builds for distribution.

Its debugging focus is live browser evidence. Agents can work with the DOM, extension-context logs, `chrome.storage`, and the list of loaded extensions rather than relying only on source inspection. The toolset also supports actions such as evaluating code in extension contexts, invoking an action button or command, and reloading an extension.

## How it works

The package runs as a local stdio MCP server, typically through `npx @extension.dev/mcp`. MCP clients send tool calls to the process, which manages local development sessions and communicates with supported browsers. By default, the server enables the local tools available on the machine; the optional platform group can be enabled with `--features=local,platform`.

Development sessions can target Chrome, Chromium, Edge, Brave, Opera, Firefox, Safari, Vivaldi, Yandex, Waterfox, Zen, Floorp, or a Chromium or Gecko binary supplied by path. Chromium-based browsers and Firefox support hot module replacement along with control, evaluation, inspection, and assertions. Safari supports development and building on macOS, but not hot module replacement or inspection.

## Setup and configuration

Add the server to a client with a command such as:

```bash
claude mcp add extension-dev -- npx @extension.dev/mcp --features=local,platform
```

The same `npx` command can be configured in Claude Desktop, Cursor, VS Code, Codex, or another MCP client that accepts stdio servers. Claude Code also provides a plugin installation path with extension-related slash commands.

Useful options include:

- `--features=local,platform` enables the platform tools in addition to local tools.
- `--no-ship` blocks publishing, promotion, shared previews, revocation, and real store submissions.
- `--project <workspace>/<project>` restricts the server to one project.
- `EXTENSION_DEV_NO_AUTO_OPEN=1` prevents approval pages from opening automatically.
- `EXTENSION_DEV_NO_TELEMETRY=1` or `DO_NOT_TRACK=1` disables the documented telemetry.

The corresponding environment settings include `EXTENSION_DEV_FEATURES`, `EXTENSION_DEV_NO_SHIP`, and `EXTENSION_DEV_PROJECT`.

## Tools and capabilities

The local tool group includes 24 tools by default, with 11 additional platform tools available when enabled. Core capabilities include:

- Scaffolding from more than 50 templates and reading template source.
- Searching Extension.js and extension.dev documentation.
- Adding an options page, popup, sidebar, or content script to an existing project.
- Starting browser development sessions with HMR where supported.
- Inspecting pages, logs, storage, loaded extensions, and runtime state.
- Evaluating code, triggering extension commands or action buttons, and reloading extensions.
- Expressing runtime expectations and receiving assertion verdicts.
- Checking manifests across browsers and producing production builds.
- Sharing previews, promoting builds, and submitting to stores through the platform lane.

The platform workflow is marked private alpha, and store submissions or stable promotions require human approval.

_Full upstream README: https://allmcps.com/mcp/mcp-291/readme_