mcp-tool.md

McpToolGuard

Restricts MCP tool invocations by name and argument size.

Actions

• GuardAction::McpTool(tool_name, args_json)

Configuration

guards:
  mcp_tool:
    allow: []                  # empty => allow all except `block`
    block:
      - "shell_exec"
      - "run_command"
    require_confirmation:
      - "git_push"
    default_action: allow      # allow|block
    max_args_size: 1048576     # bytes
    additional_allow: []
    remove_allow: []
    additional_block: []
    remove_block: []

Behavior

• block takes precedence over require_confirmation.
• If allow is non-empty, the guard operates in allowlist mode (everything else is blocked).
• require_confirmation returns a warning result (allowed but flagged).
• Argument size is computed from JSON-serialized bytes (serde_json::to_vec(args)).