What is extensiondev-mcp?

A set of tools for developing browser extensions, which are small programs that add features to web browsers.

Use it to scaffold extensions from templates, run a development server with automatic reloads, inspect page HTML and logs, and build for Chrome, Edge, or Firefox.

It supports common development work in one place, from starting a project to inspecting a live page and preparing browser-store builds.

extensiondev-mcp — Plugin by extensiondev

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Claude Code

/plugin marketplace add extensiondev/mcp

agentmods

npx agentmods add plugins/extensiondev/mcp/marketplace

Clone the repo

git clone --depth 1 https://github.com/extensiondev/mcp

Made for: Claude Code.

Per session not measured What this adds to a session before it is invoked.

When invoked not measured Not applicable: nothing here is loaded into a session.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Security

Grade A, and why

extensiondev-mcp scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude-plugin/marketplace.json · 23 lines

What it actually says

{
  "name": "extensiondev-mcp",
  "owner": {
    "name": "Cezar Augusto",
    "email": "[email protected]",
    "url": "https://extension.dev"
  },
  "plugins": [
    {
      "name": "extension-mcp",
      "source": "./",
      "description": "MCP tools for browser extension development: scaffold from 50+ templates, run the dev server with HMR, inspect the live DOM and logs, and publish store-ready builds for Chrome, Edge, and Firefox.",
      "version": "10.9.0",
      "category": "development",
      "author": {
        "name": "Cezar Augusto"
      },
      "homepage": "https://github.com/extensiondev/mcp",
      "strict": false
    }
  ]
}

Files

What ships with it

1 file beside marketplace.json in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

plugin.json 972 B

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

yesterday First seen · 23 lines scan A b49b127295f5

Subscribe to this mod's changes

extensiondev-mcp is a plugin published in the GitHub repository extensiondev/mcp (1 stars, last pushed 2d ago), licensed Apache-2.0. Its token cost is not measured: this kind of file is read by the harness, not the model. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Browser automation agents ai-agent browser-extension chrome-extension claude claude-code

extensiondev-mcp

Getting it into your agent

Grade A, and why

Nothing flagged

What it actually says

What ships with it

What this file has done since we first saw it

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