generate_diagram · PlantUML MCP Server MCP: Risk & Policy

WHAT IT DOES

What generate_diagram does on PlantUML MCP Server

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

WHY IT NEEDS A POLICY

Why generate_diagram needs a policy

This tool creates new diagram files or returns generated data, making it a Write operation. It does not execute arbitrary code, run shell commands, or delete data. The severity is low because diagram generation is non-destructive, side-effect-free creation of visualization artifacts that can be trivially replaced or deleted. An AI agent misusing this tool would simply generate unwanted diagrams, causing minimal harm.

From the tool's definition Tool generates diagram output and 'optionally saves to a file', which creates new data artifacts. The description explicitly states it 'returns the diagram as base64-encoded data and optionally saves to a file', confirming write/creation behavior.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

generate_diagram Rate-limited

generate_diagram 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": {
    "generate_diagram": {
      "limits": [
        {
          "counter": "generate_diagram_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 PlantUML MCP Server, so you can run agents against it safely.

FAQ

Questions about generate_diagram

What does the generate_diagram tool do? +

Generate a diagram from PlantUML source code. Returns the diagram as base64-encoded data and optionally saves to a file. It is categorised as a Write tool in the PlantUML 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 generate_diagram? +

Register the PlantUML MCP Server MCP server in PolicyLayer and add a rule for generate_diagram: 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 PlantUML MCP Server. Nothing to install.

What risk level is generate_diagram? +

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

Can I rate-limit generate_diagram? +

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

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

generate_diagram is provided by the PlantUML MCP Server MCP server (junqing258/plantuml-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.