variable_create · N8n Fabric MCP: Risk & Policy

WHAT IT DOES

What variable_create does on N8n Fabric

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

WHY IT NEEDS A POLICY

Why variable_create needs a policy

This tool creates new variables in the n8n automation system, which modifies the workflow configuration state reversibly. It is a write operation with potential blast radius if an agent creates variables with unintended names, values, or scope that affect workflow behavior, but does not destroy data or execute arbitrary code.

From the tool's definition Tool name is 'variable_create' and description states 'Create a new variable' — clearly a write operation that creates new data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

variable_create Rate-limited

variable_create 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": {
    "variable_create": {
      "limits": [
        {
          "counter": "variable_create_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 Fabric, so you can run agents against it safely.

FAQ

Questions about variable_create

What does the variable_create tool do? +

Create a new variable. It is categorised as a Write tool in the N8n Fabric MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on variable_create? +

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

What risk level is variable_create? +

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

Can I rate-limit variable_create? +

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

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

variable_create is provided by the N8n Fabric MCP server (ry-ops/n8n-fabric). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.