create_er_diagram · Diagram MCP: Risk & Policy

WHAT IT DOES

What create_er_diagram does on DiagramMCP

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

WHY IT NEEDS A POLICY

Why create_er_diagram needs a policy

This tool generates Entity-Relationship (ER) diagrams, which are created artifacts with no side effects beyond their generation. The output is a reversible diagram specification (likely Mermaid syntax based on the server description) that can be deleted or regenerated. It does not execute arbitrary code, delete data, or move money, making it a Write operation with low severity.

From the tool's definition Tool name is 'create_er_diagram' and is part of a diagram generation server that 'enables the dynamic generation of various software development diagrams.' The sibling tools (create_architecture_diagram, create_class_diagram, create_flowchart, etc.) all…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_er_diagram Rate-limited

create_er_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": {
    "create_er_diagram": {
      "limits": [
        {
          "counter": "create_er_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 DiagramMCP, so you can run agents against it safely.

FAQ

Questions about create_er_diagram

What does the create_er_diagram tool do? +

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

How do I enforce a policy on create_er_diagram? +

Register the Diagram MCP server in PolicyLayer and add a rule for create_er_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 DiagramMCP. Nothing to install.

What risk level is create_er_diagram? +

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

Can I rate-limit create_er_diagram? +

Yes. Add a rate_limit block to the create_er_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 create_er_diagram completely? +

Set action: deny in the PolicyLayer policy for create_er_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 create_er_diagram? +

create_er_diagram is provided by the Diagram MCP server (lelondelonmelon/diagrammcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.