MCP stdio

mcp-gateway is a single-process MCP server over stdio. It enrolls a startup bootstrap credential from environment variables, then speaks MCP protocol version 2025-11-25 on stdin/stdout. Stdout is reserved for newline-delimited JSON-RPC; diagnostics go to stderr.

Build

cargo build -p mcp-gateway --release
# binary: ./target/release/mcp-gateway

Startup credential

At process start the gateway requires all four bootstrap variables (same contract as bobby serve / bobby init):

Generate them with bobby init (writes …/bobby-browser/bootstrap.env), then either export the file into the environment or point your MCP client env at those keys. Missing or invalid startup input fails closed.

For agent hosts, default bobby init (and install / loopback auto-init) mints the agent preset: no authority:admin, marker # bobby-bootstrap-preset: agent, heal never widens past that floor. Operators who need to mint principals use bobby init --preset unrestricted. Marker-less existing files still heal as unrestricted (back-compat).

There is no single AUTOMATION_RUNTIME_TOKEN env var for stdio startup. That name is only a conventional alias for the client bearer when talking to the HTTP runtime / TypeScript SDK.

Client config example

The easy path is the installer — it writes the bootstrap credential, merges the server entry into your host's config, installs the agent skill into ~/.agents/skills/bobby-browser/ (project: .agents/skills/ with --project-skill; optional --skill-claude / --skill-openclaw), and can install the Firefox companion (extension + native host; pairing finishes via toolbar Pair, or bobby enroll-firefox-profile for CI):

bobby install                    # interactive checklist
bobby install --host claude --skill --yes   # non-interactive
# or: make install               # builds bobby + the gateway, then runs the installer

The merged entry points at bobby mcp-stdio, which loads the credential from bootstrap.env itself — the host config carries no secrets and no env wiring:

{
  "mcpServers": {
    "bobby-browser": {
      "command": "/absolute/path/to/bobby",
      "args": ["mcp-stdio"]
    }
  }
}

bobby init --emit <claude|zed|vscode|json> remains for hosts that prefer the raw mcp-gateway binary with ${VAR} placeholders; that form requires exporting the four bootstrap variables into the host's environment.

bobby doctor runs a live handshake against the gateway (initialize + tools/list) and reports the tool count and byte size against the 128 KiB catalog budget, so a dead or oversized surface is caught before the agent sees it.

Limits and lifecycle

• Frames limited to 1 MiB; tool input to 256 KiB; event reads to 256 records
• Call initialize before tools
• Cancellation, EOF, expiry, and revocation close or reject work without leaking credentials

Tool catalog: MCP tools. Multi-tenant HTTP alternative: MCP over HTTP.