set_brush_shape · Paint MCP: Risk & Policy

WHAT IT DOES

What set_brush_shape does on Paint MCP

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

WHY IT NEEDS A POLICY

Why set_brush_shape needs a policy

This tool modifies the brush shape parameter, which is a reversible configuration change to the drawing state. It does not execute arbitrary code, delete data, or cause financial transactions. It has low blast radius—misconfiguring a brush shape produces a visual artifact that can be undone (e.g., by clearing the canvas or changing the brush again).

From the tool's definition Tool name 'set_brush_shape' and server context (Pygame-based drawing canvas) indicate this modifies brush configuration state.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_brush_shape Rate-limited

set_brush_shape 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": {
    "set_brush_shape": {
      "limits": [
        {
          "counter": "set_brush_shape_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 Paint MCP, so you can run agents against it safely.

FAQ

Questions about set_brush_shape

What does the set_brush_shape tool do? +

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

How do I enforce a policy on set_brush_shape? +

Register the Paint MCP server in PolicyLayer and add a rule for set_brush_shape: 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 Paint MCP. Nothing to install.

What risk level is set_brush_shape? +

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

Can I rate-limit set_brush_shape? +

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

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

set_brush_shape is provided by the Paint MCP server (joeyballentine/paint-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.