In-Process Mode

Run the Playwright server in the same process as the MCP server for zero-overhead communication.

In-Process Mode

Run the BAP Playwright server in the same process as the MCP server, bypassing WebSocket entirely. Uses DirectTransport for zero-overhead communication.

Enable In-Process Mode

npx @browseragentprotocol/mcp --in-process

Claude Code

claude mcp add --transport stdio bap-browser -- npx -y @browseragentprotocol/mcp --in-process

How It Works

Default Mode (WebSocket)

MCP Server  --[WebSocket]--> BAP Playwright Server (child process)

The MCP server spawns a separate Playwright server process and communicates over WebSocket with JSON-RPC 2.0.

In-Process Mode (DirectTransport)

MCP Server + BAP Playwright Server (same process, DirectTransport)

The Playwright server runs in the same Node.js process. DirectTransport passes messages directly in memory — no serialization, no network, no child process.

Trade-offs

Advantages

• Lower latency (no WebSocket overhead) - No child process management - Simpler deployment (single process) - Slightly lower memory usage

Limitations

• Server-push notifications are not supported - No event streaming (console errors, network failures) - Cannot share the server with other clients - If the server crashes, the MCP server crashes too

In-process mode does not support server-push notifications. This means browser console errors and network failure events will not be forwarded to the MCP client. If you need event streaming, use the default WebSocket mode.

When to Use

Scenario	Recommended Mode
Latency-sensitive single-agent workflows	In-process
Need event streaming (console/network errors)	Default (WebSocket)
Sharing server across multiple MCP clients	Default with --url
Simple deployment, single process	In-process
Long-running monitoring tasks	Default (WebSocket)

Combining with Other Flags

In-process mode works with other MCP flags:

npx @browseragentprotocol/mcp --in-process --slim --headless
npx @browseragentprotocol/mcp --in-process --browser firefox

The --url flag is incompatible with --in-process. You cannot connect to an external server in in-process mode — the whole point is running everything in one process.