create_metafield

THE RISK

Medium Risk

Why create_metafield needs a policy

This tool creates or modifies custom metadata fields attached to business resources (products, orders, customers, etc.) in an e-commerce or order management context. It is a Write operation because it reversibly adds or modifies data.

From the tool's definition Tool description states 'Attach a metafield (custom typed field) to a resource', which is a create/modify operation on data structures. The action is reversible (metafields can be removed/updated) and does not delete or execute arbitrary code.

Documented attack patterns abuse exactly the kind of access create_metafield gives an agent:

POLICY

How to control create_metafield

PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Afip, and nothing reaches the server without passing your rules. This is the rule we recommend for create_metafield:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "create_metafield": {
      "limits": [
        {
          "counter": "create_metafield_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

create_metafield 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.

Create a free account and register Mcp Afip — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

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EXPLORE

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Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about create_metafield

What does the create_metafield tool do? +

Attach a metafield (custom typed field) to a resource (shop, product, variant, customer, order, collection, draft_order, etc). It is categorised as a Write tool in the Mcp Afip 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_metafield? +

Register the Mcp Afip MCP server in PolicyLayer and add a rule for create_metafield: 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 Mcp Afip. Nothing to install.

What risk level is create_metafield? +

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

Can I rate-limit create_metafield? +

Yes. Add a rate_limit block to the create_metafield 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_metafield completely? +

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

create_metafield is provided by the Mcp Afip MCP server (codespar/mcp-dev-latam). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Mcp Afip tool call.

Start from Mcp Afip, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →