Extensiondev MCP Server

[npm-version-url]: https://www.npmjs.com/package/@extension.dev/mcp [npm-downloads-url]: https://www.npmjs.com/package/@extension.dev/mcp. Its 30 documented tools cluster into extension, auth & access. It runs locally over stdio via the published package.

People who work with browser extension, developer tools and firefox addon and want it reachable from Claude, Cursor, VS Code, or another MCP client. The project is written in TypeScript.

VERIFIED ACTIVE

LAST COMMIT 2026-09-29 · ★ 3 · #96 OF 290 MAINTAINED BROWSER AUTOMATION · VERIFIED 2026-09-30

Apache-2.0 · TypeScript servers · how we verify → /methodology

01 · Install Extensiondev MCP Server

before you install - you'll need

The README does not document required environment variables for a basic install.

Claude Code

claude mcp add extensiondev-mcp -- npx -y @extension.dev/mcp

Claude Desktop / Cursor / VS Code - add to config

{
  "mcpServers": {
    "extensiondev-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "@extension.dev/mcp"
      ]
    }
  }
}

Same JSON for Cursor. For VS Code, rename the top-level key from `mcpServers` to `servers`.

Using another client? Same JSON, different key

Claude Desktop · mcpServers

Cursor · mcpServers

VS Code · servers

Windsurf · mcpServers

Zed · context_servers

Cline · mcpServers

Roo Code · mcpServers

Continue · mcpServers

LibreChat · mcpServers

Gemini CLI · mcpServers

Codex CLI · mcp_servers

Full setup guides: every client.

02 · Evidence

Security posture

What to check before giving this server access to your agent - from the registry, GitHub, and our own probes. We don't score safety; we show what's verifiable.

runs as local process (stdio) - runs on your machine with your user's permissions

license Apache-2.0 - declared in the repository

npm package @extension.dev/mcp - the @extension.dev scope differs from the repo owner (extensiondev); confirm it's the project's official package

registry namespace io.github.extensiondev is GitHub-verified and matches the repo owner

03 · What Extensiondev MCP Server can do

Prose above is summarized from the project's README and registry record - no invented capabilities.

What you can build

With this server connected, an agent can browse 50+ templates (list) and read one's source (source), add sidebar/popup/content script, stop a dev/start/preview session (server + browser), and list loaded extensions (Chromium and Firefox).

Capability map

Tools grouped from the project's README - what Extensiondev MCP Server lets an agent do.

Extension

29 tools - e.g. Scaffold from a template; Browse 50+ templates (list) and read one's source (source); Add sidebar/popup/content script

extension_create · extension_templates · extension_add_feature · extension_build · extension_dev · extension_start…

auth & access

1 tool - e.g. Device login at extension.dev, plus login status and logout

extension_auth

Latest releases

v10.10.0 · 2026-09-25

Safari was the one engine this server treated as a dead end, while the · Extension.js it shells out to had grown a working Safari dev loop. The client · now rides that loop, and its pinned CLI packages move to the…

v10.9.0 · 2026-08-21

The client ran its browser work through CLI packages pinned three minor · releases back, so an agent driving the MCP got 4.0.30's behavior while the · same person running extension on their own machine got 4.1.2's.…

v10.8.0 · 2026-08-17

Some MCP actions change what a public channel serves or hand something to a · store, and none of those can be taken back in place. The client now carries · an approval gate for exactly those actions, so a human can…

04 · Who maintains Extensiondev MCP Server

mcp is maintained by extensiondev. It's the only MCP server we track from this author; the repo dates to Jul 2026.

05 · Facts

repository: github.com/extensiondev/mcp
website: https://extension.dev/
category: browser automation - ranked #96 of 290 actively-maintained browser automation servers as of 2026-09-30.
release cadence: 10+ releases in the last 90 days (latest 2026-09-25)
registry: io.github.extensiondev/mcp (active, first published 2026-07-17 · 15 versions)
packages: npm:@extension.dev/mcp

06 · Extensiondev MCP Server FAQ

Is Extensiondev MCP Server still maintained?

Yes - as of 2026-09-30, its last commit was 2026-09-29 and it shipped 10+ releases in the last 90 days. We re-verify nightly.

What can Extensiondev MCP Server do?

How do I install Extensiondev MCP Server?

Run `npx -y @extension.dev/mcp`. The README does not document required environment variables for a basic install. You can also paste the ready-made client config above.

Does Extensiondev MCP Server run locally?

Yes - it's a stdio server: it runs on your machine (via npx) with your user's permissions. Your data stays local unless the server itself calls external APIs.

07 · Alternatives to Extensiondev MCP Server

Alternatives to Extensiondev MCP Server

Maintained browser automation servers if Extensiondev MCP Server isn't the fit.

Pairs well with

Servers that cover what Extensiondev MCP Server doesn't - only shown when the pairing reason fits the companion.

More browser automation MCP servers · Extentos MCP Server · Lan Direct · E2e Runner

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