create_variable · N8n MCP: Risk & Policy

WHAT IT DOES

What create_variable does on N8n

AI agents use create_variable to create or update resources in N8n — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your N8n environment.

WHY IT NEEDS A POLICY

Why create_variable needs a policy

This tool creates a new instance variable, which is a reversible write operation. It modifies the n8n automation system's configuration/state by adding a new variable, but does not delete, execute arbitrary code, or move money. The write_mode requirement shows it's gated as a write operation.

From the tool's definition Tool description explicitly states 'Create a new instance variable' - this is a create operation that adds new data to the n8n system. The requirement for 'write_mode' protection confirms it performs a reversible modification rather than a destructive action.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_variable Rate-limited

create_variable 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_variable": {
      "limits": [
        {
          "counter": "create_variable_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 N8n, so you can run agents against it safely.

FAQ

Questions about create_variable

What does the create_variable tool do? +

Create a new instance variable. Requires write_mode. It is categorised as a Write tool in the N8n 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_variable? +

Register the N8n MCP server in PolicyLayer and add a rule for create_variable: 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 N8n. Nothing to install.

What risk level is create_variable? +

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

Can I rate-limit create_variable? +

Yes. Add a rate_limit block to the create_variable 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_variable completely? +

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

create_variable is provided by the N8n MCP server (siddharth0903/n8n-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.