mcp-cdp

mcp-cdp

A safe-by-default Model Context Protocol server that drives an Electron or Chrome/Chromium app over the Chrome DevTools Protocol (CDP) — instead of pixel-level GUI automation. Point it at the app's --remote-debugging-port and an agent gets the DOM, console, network requests, real input (click / type / navigate), and — gated — JavaScript evaluation.

Why this beats computer-use for a desktop/web app:

• The DOM, not a screenshot. The agent reads exact rendered HTML and can query any element — far more information, and it sees things that aren't on screen.
• Console + network. When a test fails, the uncaught exception or the failed request is right there — no guessing from an image.
• No collisions. Each agent attaches to its own debugging port, so parallel agents (e.g. one per git worktree) never fight over one desktop.
• Cross-OS. CDP works identically on macOS, Linux and Windows — the same flow runs on a headless VPS.

Part of the dockndevai MCP server suite — one governance model across all of them.

What it gives an agent

Starts read-only (see Safe by default); higher-capability tools are only registered when you raise the mode.

Tool	For	Needs mode
list_targets	list pages / webviews / Electron windows (id, type, title, url)	read-only
dom_snapshot	rendered HTML of the page or a selector's subtree	read-only
query_dom	outer HTML of every element matching a CSS selector	read-only
console_logs	recent console output + uncaught exceptions	read-only
network_requests	recent requests (method, url, status, mime; headers never captured)	read-only
screenshot	a PNG of the viewport	read-only
click	click the first element matching a selector	read-write
type_text	type into the page (focus a selector first)	read-write
press_key	Enter / Tab / Escape / Backspace / Delete / Arrows	read-write
navigate	navigate a target to a URL (confirmed)	read-write
evaluate	run a JavaScript expression in the page	admin + CDP_ALLOW_EVAL

Install

npx -y @dockndevai/mcp-cdp

Expose a debugging port

Start your app (or a worktree's dev build) with an explicit port — one per agent:

• Electron app: your-app --remote-debugging-port=9222, or in main-process code app.commandLine.appendSwitch('remote-debugging-port', '9222') before app.whenReady().
• Plain Chrome/Chromium: chrome --headless=new --remote-debugging-port=9222 --user-data-dir=/tmp/p1 <url>.

Check it's up: curl http://127.0.0.1:9222/json/version.

Configure

{
  "mcpServers": {
    "cdp": {
      "command": "npx",
      "args": ["-y", "@dockndevai/mcp-cdp"],
      "env": {
        "CDP_PORT": "9222",
        "CDP_MODE": "read-only"
      }
    }
  }
}

See docs/CLIENTS.md for Claude Code / Cursor / Codex / VS Code / Windsurf, and .env.example for every variable.

Safe by default

Enforced by src/security.ts. The browser process is the real boundary — this keeps an agent inside the targets and actions you intend:

• CDP_MODE — read-only (default) → read-write → admin. Tools above the mode aren't registered, so in read-only the agent cannot click, type or navigate at all.
• CDP_TARGET_ALLOWLIST — confine interactions to targets whose URL matches your patterns (empty = all). Reads (inspection) are always allowed.
• CDP_PROTECTED_TARGETS — targets that can be inspected but never interacted with. Defaults protect sign-in pages (accounts.google.com, login.microsoftonline.com, …) and browser internals (chrome://, devtools://, extensions).
• CDP_ALLOW_EVAL — evaluate is arbitrary code execution in the renderer: admin mode plus this flag, refused on protected targets, with a human confirmation.
• CDP_DRY_RUN — interactions log their intent and return without dispatching.
• Secrets — request/response headers are never captured (cookies/auth), and sensitive URL query values are redacted. evaluate and navigate also prompt a human via MCP elicitation.
• Loopback only — the endpoint must be 127.0.0.1 unless CDP_ALLOW_REMOTE=true.

Optional AI risk guard. Set CDP_GUARD_MODE=monitor|enforce to have the evaluate tool consult a local laya-guard daemon (pipx install laya-guard && laya-guard) that classifies the JS expression allow/confirm/block before it runs. It runs after the eval gate and can only tighten, never grant; fails closed.

There is a bundled skill, cdp-safe-operations, that teaches an agent how to expose a port, read the DOM/console/network instead of screenshots, the safety rules, and the "why did this fail?" workflow. See also SECURITY.md.

Developing

npm install
npm run build
# list the tools:
echo '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}' | CDP_PORT=9222 node dist/index.js
npm test

Licence

MIT