AI agents use export_stl to create or update resources in Mcp Freecad — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mcp Freecad environment.
The tool creates a new file by exporting CAD objects to STL format. This is a Write operation—it produces a new artifact (file) on the system. The severity is medium because while file creation is reversible (files can be deleted), unintended exports could fill disk space, overwrite existing files, or create thousands of unwanted model files if an agent misuses the parameters.
From the tool's definition Tool name 'export_stl' and description 'Export objects to STL file' indicate file creation/writing. STL (Stereolithography) is a 3D model file format commonly used for 3D printing and CAD work.
Documented attack patterns abuse exactly the kind of access export_stl gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Freecad, and nothing reaches the server without passing your rules. This is the rule we recommend for export_stl:
{
"version": "1",
"default": "deny",
"tools": {
"export_stl": {
"limits": [
{
"counter": "export_stl_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}export_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.
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Export objects to STL file. It is categorised as a Write tool in the Mcp Freecad MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mcp Freecad MCP server in PolicyLayer and add a rule for export_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 Mcp Freecad. Nothing to install.
export_stl is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the export_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.
Set action: deny in the PolicyLayer policy for export_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.
export_stl is provided by the Mcp Freecad MCP server (jango-blockchained/mcp-freecad). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Mcp Freecad, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
34 Mcp Freecad tools catalogued and risk-classified — across an index of 43,000+ MCP servers.