n8n_create_variable · n8n MCP Server MCP: Risk & Policy

WHAT IT DOES

What n8n_create_variable does on n8n MCP Server

AI agents use n8n_create_variable to create or update resources in n8n MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your n8n MCP Server environment.

WHY IT NEEDS A POLICY

Why n8n_create_variable needs a policy

This tool creates and stores data (a new global variable) that persists and affects workflow execution across the entire n8n instance. While reversible (variables can be deleted), it modifies the workflow configuration state in a way that impacts all workflows.

From the tool's definition Tool 'n8n_create_variable' creates a new global workflow variable that is accessible across all workflows via $vars.key. The description explicitly states it creates a new variable, and the arguments show it accepts a key-value pair for storage.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

n8n_create_variable Rate-limited

n8n_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": {
    "n8n_create_variable": {
      "limits": [
        {
          "counter": "n8n_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 MCP Server, so you can run agents against it safely.

FAQ

Questions about n8n_create_variable

What does the n8n_create_variable tool do? +

Create a new global workflow variable accessible in all workflows via \$vars.key. Args: - key (string): Variable key/name - value (string): Variable value - type (string?): Variable type (default. It is categorised as a Write tool in the n8n 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 n8n_create_variable? +

Register the n8n MCP Server MCP server in PolicyLayer and add a rule for n8n_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 MCP Server. Nothing to install.

What risk level is n8n_create_variable? +

n8n_create_variable is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit n8n_create_variable? +

Yes. Add a rate_limit block to the n8n_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 n8n_create_variable completely? +

Set action: deny in the PolicyLayer policy for n8n_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 n8n_create_variable? +

n8n_create_variable is provided by the n8n MCP Server MCP server (verzth/mcp-n8n). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.