brush_turn · Open Brush MCP Server MCP: Risk & Policy

WHAT IT DOES

What brush_turn does on Open Brush MCP Server

AI agents invoke brush_turn to trigger actions in Open Brush MCP Server. 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 brush_turn needs a policy

This tool sends a command to the Open Brush HTTP API to rotate the brush relative to its current orientation. It triggers an external operation in a running application, fitting the Execute category. The blast radius is low as it only affects the current brush orientation in a 3D painting session, with no financial, destructive, or persistent data modification implications.

From the tool's definition 'Turns brush relatively' — triggers an external operation (rotating/turning the brush in the Open Brush application via HTTP API)

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

brush_turn Rate-limited

brush_turn 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": {
    "brush_turn": {
      "limits": [
        {
          "counter": "brush_turn_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 Open Brush MCP Server, so you can run agents against it safely.

FAQ

Questions about brush_turn

What does the brush_turn tool do? +

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

How do I enforce a policy on brush_turn? +

Register the Open Brush MCP Server MCP server in PolicyLayer and add a rule for brush_turn: 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 Open Brush MCP Server. Nothing to install.

What risk level is brush_turn? +

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

Can I rate-limit brush_turn? +

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

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

brush_turn is provided by the Open Brush MCP Server MCP server (moz411/openbrush-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.