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IBM

Physics MCP Server

by IBM

step_simulation

Advance a physics simulation by a given number of steps and retrieve the complete state of all bodies, including positions, velocities, and contacts.

Instructions

Step the simulation forward in time.

Advances the physics simulation by running the integrator for N steps.
Returns the complete state of all bodies after stepping.

Args:
    sim_id: Simulation ID
    steps: Number of timesteps to simulate. Default 1.
        Example: steps=600 with dt=0.016 = 9.6 seconds of simulation
    dt: Optional timestep override (seconds). If None, uses config default.

Returns:
    SimulationStepResponse containing:
        - sim_id: Simulation identifier
        - time: Current simulation time in seconds
        - bodies: List of all body states with positions, velocities, contacts

Tips for LLMs:
    - Each body state includes position, orientation (quaternion), velocities
    - contacts array shows active collisions with impulse magnitudes
    - For real-time preview: steps=1, call repeatedly
    - For final result: steps=1000+, call once
    - Large step counts may timeout - limit to ~10,000 steps per call

Example:
    # Simulate 10 seconds at 60 FPS
    result = await step_simulation(
        sim_id=sim_id,
        steps=600  # 600 steps × 0.016s = 9.6s
    )
    for body in result.bodies:
        print(f"{body.id}: position={body.position}")

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
sim_idYes
stepsNo
dtNo
Behavior5/5

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

No annotations are provided, so the description fully discloses behavioral traits: it advances simulation, returns complete state, includes timeout limits, and describes the return structure (SimulationStepResponse with bodies, time, etc.).

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

Conciseness5/5

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

The description is well-structured with a summary, parameter details, return info, tips, and example. Every sentence adds value without redundancy.

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 completely covers return types and provides tips for effective use. Given the moderate complexity of a simulation stepping tool, it is fully complete.

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 no descriptions (0% coverage), but the description explains each parameter's meaning: sim_id is the simulation ID, steps is number of timesteps with default and example, dt is optional timestep override. This fully compensates for missing schema descriptions.

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 steps the simulation forward in time using a specific verb ('step') and resource ('simulation'). It distinguishes from sibling tools like 'create_simulation' and 'destroy_simulation'.

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 tips on when to use specific step counts ('real-time preview' vs 'final result') and warns about timeouts for large steps. However, it does not explicitly state when not to use this tool or mention alternatives.

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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