Fix (lock) a point or geometry in place. Args: sketch_name: Name of the sketch. geometry_index: Index of the geometry element. point_index: Point to fix (1=start, 2=end, 3=center). -1 to fix the entire element. doc_name: Document containing the sketch. Uses active document if None. Returns: Dicti...
AI agents use constrain_fix to create or update resources in FreeCAD Robust MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your FreeCAD Robust MCP Server environment.
This tool adds a constraint to a sketch geometry in FreeCAD, which is a reversible write operation (constraints can be deleted). It modifies the document by locking a point or geometry element in place, but does not execute code or irreversibly destroy data.
From the tool's definition Fix (lock) a point or geometry in place... Returns: constraint_index: Index of the added constraint
Risk signalsBulk/mass operation — affects multiple targets
Documented attack patterns abuse exactly the kind of access constrain_fix gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and FreeCAD Robust MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for constrain_fix:
{
"version": "1",
"default": "deny",
"tools": {
"constrain_fix": {
"limits": [
{
"counter": "constrain_fix_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}constrain_fix 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.
Free to start. No card required.
Fix (lock) a point or geometry in place. Args: sketch_name: Name of the sketch. geometry_index: Index of the geometry element. point_index: Point to fix (1=start, 2=end, 3=center). -1 to fix the entire element. doc_name: Document containing the sketch. Uses active document if None. Returns: Dictionary with constraint info: - constraint_index: Index of the added constraint. It is categorised as a Write tool in the FreeCAD Robust MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the FreeCAD Robust MCP Server MCP server in PolicyLayer and add a rule for constrain_fix: 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 Robust MCP Server. Nothing to install.
constrain_fix 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 constrain_fix 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 constrain_fix. 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.
constrain_fix is provided by the FreeCAD Robust MCP Server MCP server (spkane/freecad-addon-robust-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 152 FreeCAD Robust MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
152 FreeCAD Robust MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.