brush_add_size · Open Brush MCP Server MCP: Risk & Policy

WHAT IT DOES

What brush_add_size does on Open Brush MCP Server

AI agents use brush_add_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_add_size needs a policy

This tool changes a brush property (size) within the 3D painting application. It modifies state but is reversible (size can be changed back), has no destructive, financial, or execution implications, and the blast radius is low — worst case is an undesired brush size in a painting session.

From the tool's definition Modifies brush size by an amount

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

brush_add_size Rate-limited

brush_add_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_add_size": {
      "limits": [
        {
          "counter": "brush_add_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_add_size

What does the brush_add_size tool do? +

Modifies brush size by an amount. 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_add_size? +

Register the Open Brush MCP Server MCP server in PolicyLayer and add a rule for brush_add_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_add_size? +

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

Can I rate-limit brush_add_size? +

Yes. Add a rate_limit block to the brush_add_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_add_size completely? +

Set action: deny in the PolicyLayer policy for brush_add_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_add_size? +

brush_add_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.