fem_run · FreeCAD MCP: Risk & Policy

WHAT IT DOES

What fem_run does on FreeCAD MCP

AI agents invoke fem_run to trigger actions in FreeCAD MCP. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why fem_run needs a policy

This tool triggers execution of external finite element simulations whose outcomes depend on input parameters (mesh configuration, material properties, boundary conditions, etc.). Such execution can consume significant computational resources and produce results that guide downstream decisions. While not destructive of data and not financial, it represents a computational operation with real-world consequences.

From the tool's definition Tool name 'fem_run' indicates execution of finite element method (FEM) simulations. The server description mentions 'structural analysis' as a capability, and 'fem_run' is positioned among tools that create BIM objects and perform complex CAD operations.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fem_run Rate-limited

fem_run stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "fem_run": {
      "limits": [
        {
          "counter": "fem_run_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches FreeCAD MCP, so you can run agents against it safely.

FAQ

Questions about fem_run

What does the fem_run tool do? +

fem_run. It is categorised as a Execute tool in the FreeCAD MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on fem_run? +

Register the FreeCAD MCP server in PolicyLayer and add a rule for fem_run: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches FreeCAD MCP. Nothing to install.

What risk level is fem_run? +

fem_run is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit fem_run? +

Yes. Add a rate_limit block to the fem_run rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block fem_run completely? +

Set action: deny in the PolicyLayer policy for fem_run. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides fem_run? +

fem_run is provided by the FreeCAD MCP server (sandraschi/freecad-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.