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):

Variable	Purpose
`AUTOMATION_RUNTIME_BOOTSTRAP_TOKEN`	High-entropy plaintext bearer (32–505 printable ASCII bytes)
`AUTOMATION_RUNTIME_BOOTSTRAP_PRINCIPAL`	Principal UUID
`AUTOMATION_RUNTIME_BOOTSTRAP_CAPABILITIES`	Comma-separated capability wire strings
`AUTOMATION_RUNTIME_BOOTSTRAP_EXPIRES_AT`	RFC3339 expiry

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.

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

{
  "mcpServers": {
    "bobby-browser": {
      "command": "/absolute/path/to/mcp-gateway",
      "env": {
        "AUTOMATION_RUNTIME_BOOTSTRAP_TOKEN": "${AUTOMATION_RUNTIME_BOOTSTRAP_TOKEN}",
        "AUTOMATION_RUNTIME_BOOTSTRAP_PRINCIPAL": "${AUTOMATION_RUNTIME_BOOTSTRAP_PRINCIPAL}",
        "AUTOMATION_RUNTIME_BOOTSTRAP_CAPABILITIES": "${AUTOMATION_RUNTIME_BOOTSTRAP_CAPABILITIES}",
        "AUTOMATION_RUNTIME_BOOTSTRAP_EXPIRES_AT": "${AUTOMATION_RUNTIME_BOOTSTRAP_EXPIRES_AT}"
      }
    }
  }
}

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.