fem_set_constraint · FreeCAD MCP: Risk & Policy

WHAT IT DOES

What fem_set_constraint does on FreeCAD MCP

AI agents use fem_set_constraint to create or update resources in FreeCAD MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your FreeCAD MCP environment.

WHY IT NEEDS A POLICY

Why fem_set_constraint needs a policy

The name suggests setting a constraint in a FEM (structural/fluid analysis) simulation setup, which is a write/configuration operation modifying simulation parameters. Description is empty, lowering confidence. Most likely Write since it 'sets' a constraint value in a model, but cannot rule out Execute if it triggers analysis.

From the tool's definition Tool name 'fem_set_constraint' on a FreeCAD MCP server with FEM (Finite Element Method) context; description is empty.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fem_set_constraint Rate-limited

fem_set_constraint stays usable, but capped — an agent stuck in a loop can't make hundreds of changes 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_set_constraint": {
      "limits": [
        {
          "counter": "fem_set_constraint_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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_set_constraint

What does the fem_set_constraint tool do? +

fem_set_constraint. It is categorised as a Write tool in the FreeCAD MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on fem_set_constraint? +

Register the FreeCAD MCP server in PolicyLayer and add a rule for fem_set_constraint: 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_set_constraint? +

fem_set_constraint is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit fem_set_constraint? +

Yes. Add a rate_limit block to the fem_set_constraint 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_set_constraint completely? +

Set action: deny in the PolicyLayer policy for fem_set_constraint. 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_set_constraint? +

fem_set_constraint 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.