xbrl_create_instance · Arelle MCP: Risk & Policy

WHAT IT DOES

What xbrl_create_instance does on Arelle

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

WHY IT NEEDS A POLICY

Why xbrl_create_instance needs a policy

XBRL instance documents are structured financial filings that encode company facts and metrics. Creating a new instance is a write operation that generates new financial data artifacts.

From the tool's definition Tool name 'xbrl_create_instance' indicates creation of a new XBRL instance document. The verb 'create' paired with 'instance' in the context of XBRL financial filings suggests generation of new structured financial data artifacts.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

xbrl_create_instance Rate-limited

xbrl_create_instance 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": {
    "xbrl_create_instance": {
      "limits": [
        {
          "counter": "xbrl_create_instance_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Arelle, so you can run agents against it safely.

FAQ

Questions about xbrl_create_instance

What does the xbrl_create_instance tool do? +

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

How do I enforce a policy on xbrl_create_instance? +

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

What risk level is xbrl_create_instance? +

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

Can I rate-limit xbrl_create_instance? +

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

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

xbrl_create_instance is provided by the Arelle MCP server (thekinghippopotamus/arelle-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.