> ## Documentation Index
> Fetch the complete documentation index at: https://bedrockdynamics.studio/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# MCP Tools

> Model Context Protocol tools available in each sim container.

roz uses the [Model Context Protocol (MCP)](https://modelcontextprotocol.io/) to discover and call robot-specific tools at runtime. Each Docker sim container bundles an MCP server on port 8090 that exposes tools tailored to the robot's capabilities.

## How Tool Discovery Works

When you start a simulation with `roz sim start`, the following happens:

1. The Docker container starts with Gazebo, the robot's middleware stack, and an MCP server.
2. The agent connects to the MCP server on port 8090.
3. The agent calls `tools/list` to discover available tools and their schemas.
4. Discovered tools are registered with the agent session via `RegisterTools`.

Tools are scoped to the container that provides them. When a container stops, its tools are automatically unregistered from the session.

## ros2-manipulator

Tools for controlling a 6-DOF arm (UR5) via MoveIt2.

| Tool                   | Description                                                                  | Parameters                                |
| ---------------------- | ---------------------------------------------------------------------------- | ----------------------------------------- |
| `get_joint_state`      | Returns current joint positions and velocities for all 6 joints.             | None                                      |
| `move_to_named_target` | Moves the arm to a predefined named pose (e.g. `"home"`, `"up"`, `"ready"`). | `target: string`                          |
| `move_to_pose`         | Plans and executes a motion to a Cartesian pose.                             | `x, y, z: float`, `qx, qy, qz, qw: float` |
| `stop_arm`             | Immediately stops all arm motion.                                            | None                                      |

```bash theme={null}
# Example: move to home position
# The agent calls this tool automatically when you say "move to home"
{
  "name": "move_to_named_target",
  "parameters": { "target": "home" }
}
```

## px4-gazebo-humble

The PX4 drone container uses gRPC (MAVSDK) for flight commands rather than MCP. The agent communicates with the PX4 autopilot through a gRPC bridge that translates high-level commands to MAVLink.

| Command        | Description                                     | Parameters             |
| -------------- | ----------------------------------------------- | ---------------------- |
| `arm`          | Arms the drone motors.                          | None                   |
| `takeoff`      | Arms and takes off to a specified altitude.     | `altitude: float`      |
| `land`         | Lands at current position.                      | None                   |
| `go_to`        | Flies to a GPS or local coordinate.             | `lat, lon, alt: float` |
| `set_offboard` | Enters offboard mode for WASM velocity control. | None                   |

<Note>
  PX4 flight commands go through gRPC, not MCP. The agent handles this difference transparently — you give the same natural language instructions regardless of the underlying protocol.
</Note>

## ardupilot-gazebo

The ArduPilot drone container provides similar flight commands through its own interface.

| Command   | Description                                 | Parameters        |
| --------- | ------------------------------------------- | ----------------- |
| `arm`     | Arms the drone motors.                      | None              |
| `takeoff` | Arms and takes off to a specified altitude. | `altitude: float` |
| `land`    | Lands at current position.                  | None              |
| `go_to`   | Flies to a local coordinate.                | `x, y, z: float`  |

## ros2-nav2

Tools for controlling a differential drive mobile robot via the Nav2 stack.

| Tool               | Description                                                                       | Parameters                  |
| ------------------ | --------------------------------------------------------------------------------- | --------------------------- |
| `navigate_to`      | Sends a navigation goal to Nav2. The robot plans a path and drives to the target. | `x, y: float`, `yaw: float` |
| `follow_waypoints` | Sends a sequence of waypoints for the robot to follow in order.                   | `waypoints: [{x, y, yaw}]`  |

## Custom MCP Servers

If you build a custom sim container, you can bundle your own MCP server. The agent discovers tools from any MCP server that:

1. Listens on port 8090 inside the container.
2. Implements the MCP `tools/list` and `tools/call` endpoints.
3. Returns valid JSON Schema for each tool's parameters.

The MCP server can also provide a `substrate:workflow` prompt that gives the agent context about how to use the tools together. This prompt is injected into the agent's system context when the tools are registered.

## MCP vs WASM

MCP tools operate at 1-3Hz — they are discrete actions like "move to this pose" or "navigate to this point." For continuous, closed-loop control at 100Hz, the agent writes WASM controllers that use the [channel interface](/roz/reference/channel-manifests) instead.

The agent chooses between MCP tools and WASM controllers based on the task. Simple discrete actions use MCP. Continuous or reactive behaviors use WASM. The agent can combine both in a single session.