Jet Browser Verifier

Jet Browser MCP verifier

This local stdio server gives an MCP client one narrow way to verify Jet Browser. Its multi-platform package selects a native linux/amd64 or linux/arm64 image, disables browser networking, opens the image's local fixture, types through native input, checks the DOM, captures a fresh PNG, and cleans up.

It is a runtime verifier, not a general browsing server. It does not expose public-web navigation, CDP, personal browser profiles, credentials, a hosted service, or telemetry.

Requirements

• Node.js 24+
• Docker
• An x86_64 or ARM64 Linux host

The first verification may pull the public image from GHCR. Browser execution itself uses Docker's --network=none boundary. The image is pinned by digest in server.mjs.

Install from the OCI package

The versioned MCP image starts the stdio server directly. It needs the Docker socket only when jet_browser_verify launches the separately isolated WPE WebKit runtime:

{
  "mcpServers": {
    "jet-browser": {
      "command": "docker",
      "args": [
        "run", "--rm", "-i", "--network=none",
        "--mount", "type=bind,src=/var/run/docker.sock,dst=/var/run/docker.sock",
        "ghcr.io/masakaai/jet-browser-mcp:0.9.0"
      ]
    }
  }
}

Docker socket grants host-level control. Configure this local server only for a trusted MCP client. The outer MCP container has networking disabled, and the browser container it launches independently uses --network=none, resource limits, reduced capabilities, and deterministic cleanup.

The package metadata for the official MCP Registry is server.json. The OCI image carries the matching io.modelcontextprotocol.server.name ownership annotation.

Install from source

git clone https://github.com/masakaai/jet-browser.git
cd jet-browser
npm ci

Add the server to an MCP client with an absolute checkout path:

{
  "mcpServers": {
    "jet-browser": {
      "command": "node",
      "args": ["/absolute/path/to/jet-browser/integrations/mcp/server.mjs"]
    }
  }
}

The process speaks MCP on stdout and writes operational errors only to stderr. It exits when the client closes stdin.

Tools

Tool	Behavior
jet_browser_capabilities	Returns the pinned image, platform, evidence contract, and explicit non-capabilities without starting Docker.
jet_browser_verify	Runs one bounded verification and returns startup, native-input, DOM, screenshot, network, and image evidence.

Only one verification can run at a time. A client-side cancellation aborts the child process. The server caps child output and total runtime; failures are returned as MCP tool errors rather than protocol failures.

A successful call returns structured content like:

{
  "status": "passed",
  "network": "disabled",
  "title": "Jet Browser Ready",
  "input": "open-source runtime",
  "screenshotBytes": 2048,
  "image": "ghcr.io/masakaai/jet-browser@sha256:5884204e128a3e5bb17634078affdf28d1933d2745752cee3bc74235ed316cec"
}

The screenshot byte count varies. A pass requires at least 1,000 decoded PNG bytes and exact agreement among the expected page title, native text input, and DOM state.

Verify the integration

The protocol test starts the real stdio server, performs an MCP handshake, lists its tools, and calls the capability tool without requiring Docker:

node --test test/mcp-server.test.mjs

The repository's standalone CI remains the end-to-end runtime proof. To execute that same Docker acceptance locally:

JET_BROWSER_IMAGE=ghcr.io/masakaai/jet-browser@sha256:5884204e128a3e5bb17634078affdf28d1933d2745752cee3bc74235ed316cec \
npm run standalone:smoke

Security boundary

• The MCP call accepts no command, URL, image, profile, or path argument.
• The child process receives only the Docker connection variables it needs; application secrets are not forwarded.
• The container has browser networking disabled, bounded CPU, memory, PIDs, shared memory, and capabilities, and is removed after the check.
• The verifier never attaches to a running personal browser.
• Treat Docker access as privileged host access. Only configure this server for trusted local MCP clients.

For a broader embedding boundary, use Jet Browser's versioned tool declarations in sdk/tools.mjs and supervise each isolated container from your own harness.