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IBM

Physics MCP Server

by IBM

create_simulation

Initialize a new rigid-body physics world with configurable gravity, timestep, dimensions, and integration method. Returns a simulation ID for subsequent operations.

Instructions

Create a new physics simulation using Rapier engine.

Initializes a new rigid-body physics world with configurable gravity and
timestep. Returns a simulation ID used for all subsequent operations.

Args:
    gravity_x: X component of gravity vector (m/s²). Default 0.0
    gravity_y: Y component of gravity vector (m/s²). Default -9.81 (Earth down)
    gravity_z: Z component of gravity vector (m/s²). Default 0.0
    dimensions: 2 or 3 for 2D/3D simulation. Default 3.
    dt: Simulation timestep in seconds. Default 0.016 (60 FPS).
        Smaller = more accurate but slower, larger = faster but less stable
    integrator: Integration method. Options: "euler", "verlet", "rk4". Default "verlet".

Returns:
    SimulationCreateResponse containing:
        - sim_id: Unique simulation identifier (use for all other sim calls)
        - config: Echo of the configuration used

Tips for LLMs:
    - Keep simulation IDs in memory for the conversation session
    - Default gravity is Earth standard (9.81 m/s² down = -Y direction)
    - dt=0.016 ≈ 60 FPS, dt=0.008 ≈ 120 FPS (higher accuracy)
    - "verlet" integrator is good default (stable, energy-conserving)
    - Remember to destroy_simulation when done to free resources

Requires:
    - Rapier provider must be configured (see config.py)
    - Rapier service must be running (see RAPIER_SERVICE.md)

Example:
    # Create simulation with Earth gravity
    sim = await create_simulation(
        gravity_y=-9.81,
        dt=0.016
    )
    # Use sim.sim_id for add_body, step_simulation, etc.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
gravity_xNo
gravity_yNo
gravity_zNo
dimensionsNo
dtNo
integratorNoverlet
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description fully discloses that it creates a new physics world and returns a simulation ID for subsequent operations. It mentions resource freeing and default gravity direction. It could improve by noting that calling it multiple times creates independent simulations, but overall it is transparent about effects and prerequisites.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured with sections for Args, Returns, Tips, Requirements, and Example. It is front-loaded with the core purpose. While slightly verbose, every sentence adds value, and the structure aids readability. A minor reduction in redundancy (e.g., tips and args overlap slightly) would earn a 5.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Despite no output schema, the description details the return format (sim_id and config) and provides an example. It covers requirements, practical tips (ID memory, integrator choice), and cleanup. Given the tool's complexity (6 parameters, many siblings), the description is complete and leaves no critical gaps.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 0% description coverage, so the description carries the full burden. It thoroughly explains each parameter with units, defaults, and practical meaning (e.g., dt accuracy trade-off, gravity components, integrator options). This goes well beyond the schema and helps the agent choose correct values.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool creates a new physics simulation using the Rapier engine, initializing a rigid-body world with configurable gravity and timestep. It distinguishes itself from sibling tools (e.g., add_body, step_simulation) by being the entry point, and the example and tips reinforce its role.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear context on when to use the tool: before other simulation operations, and it warns to destroy when done. Requirements (Rapier provider configured, service running) and tips (keep IDs) guide usage. However, it does not explicitly state when not to use it or compare to alternatives, though among siblings it is unique.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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