draw_line · Paint MCP: Risk & Policy

WHAT IT DOES

What draw_line does on Paint MCP

AI agents use draw_line 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 draw_line needs a policy

The tool modifies canvas state by adding visual content, which is a write operation. It is not destructive because the changes are reversible using existing canvas operations. It has minimal blast radius—an incorrect line placement affects only the local drawing buffer, not external systems or data. Severity is low because erroneous lines are easily corrected without data loss or operational impact.

From the tool's definition Tool creates and modifies pixel data on the canvas through line drawing: 'Draw a line from (x1, y1) to (x2, y2)'. This is a reversible modification (canvas can be cleared via clear_canvas or drawn over) with no permanent destruction or external side effects.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

draw_line Rate-limited

draw_line 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": {
    "draw_line": {
      "limits": [
        {
          "counter": "draw_line_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 draw_line

What does the draw_line tool do? +

Draw a line from (x1, y1) to (x2, y2). 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 draw_line? +

Register the Paint MCP server in PolicyLayer and add a rule for draw_line: 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 draw_line? +

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

Can I rate-limit draw_line? +

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

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

draw_line 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.