step_to_stl · FreeCAD MCP: Risk & Policy

WHAT IT DOES

What step_to_stl does on FreeCAD MCP

AI agents use step_to_stl 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 step_to_stl needs a policy

Converting a STEP file to STL creates a new derived artifact (the STL file) without irreversibly modifying or deleting the original. This is a write-class operation that creates or modifies data reversibly. Severity is medium because misconfigured conversions could produce defective 3D print files (wasted materials, time), but no permanent deletion or financial impact occurs.

From the tool's definition Tool name 'step_to_stl' indicates conversion of STEP CAD format to STL (stereolithography) format. The sibling tools on this server (bim_create_*, bim_export_*) and server description confirming 'part conversion' and '3D printing slicing' operations establish…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

step_to_stl Rate-limited

step_to_stl 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": {
    "step_to_stl": {
      "limits": [
        {
          "counter": "step_to_stl_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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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 step_to_stl

What does the step_to_stl tool do? +

step_to_stl. 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 step_to_stl? +

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

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

Can I rate-limit step_to_stl? +

Yes. Add a rate_limit block to the step_to_stl 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 step_to_stl completely? +

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

step_to_stl 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.