brush_set_size · Open Brush MCP Server MCP: Risk & Policy

WHAT IT DOES

What brush_set_size does on Open Brush MCP Server

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

WHY IT NEEDS A POLICY

Why brush_set_size needs a policy

This tool changes the brush size setting in Open Brush, which is a reversible modification to application state. It does not delete data, execute code, or involve financial transactions. The blast radius is low since it only affects a brush parameter that can be easily changed again.

From the tool's definition 'Sets brush size' — modifies a brush property (size) in the 3D painting application

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

brush_set_size Rate-limited

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

FAQ

Questions about brush_set_size

What does the brush_set_size tool do? +

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

How do I enforce a policy on brush_set_size? +

Register the Open Brush MCP Server MCP server in PolicyLayer and add a rule for brush_set_size: 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_set_size? +

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

Can I rate-limit brush_set_size? +

Yes. Add a rate_limit block to the brush_set_size 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_set_size completely? +

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

brush_set_size 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.