create_entity · Narrarium MCP: Risk & Policy

WHAT IT DOES

What create_entity does on Narrarium

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

WHY IT NEEDS A POLICY

Why create_entity needs a policy

This tool creates new markdown files representing entities within a local book repository. Creation is reversible (files can be edited or deleted), and the effects are limited to adding structured data to a local repository without executing code, deleting critical data, or causing external side effects.

From the tool's definition Tool description states it creates 'a canonical entity markdown file inside the local book repository' for 'quick stubs, items, locations, factions, secrets, and timeline events.' The verb 'create' and action of writing new files to the repository indicate a…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_entity Rate-limited

create_entity 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_entity": {
      "limits": [
        {
          "counter": "create_entity_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 Narrarium, so you can run agents against it safely.

FAQ

Questions about create_entity

What does the create_entity tool do? +

Create a canonical entity markdown file inside the local book repository. Use this for quick stubs, items, locations, factions, secrets, and timeline events. Prefer create_character for full story characters. It is categorised as a Write tool in the Narrarium 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_entity? +

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

What risk level is create_entity? +

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

Can I rate-limit create_entity? +

Yes. Add a rate_limit block to the create_entity 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_entity completely? +

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

create_entity is provided by the Narrarium MCP server (narrarium-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.