add_opt_out

THE RISK

Medium Risk

Why add_opt_out needs a policy

This tool modifies user communication preferences by adding a phone number to a suppression list. While reversible (a number could theoretically be removed), it durably changes system state affecting future message delivery. It is not destructive (no irreversible deletion), not financial, and not execute-class.

From the tool's definition Tool name 'add_opt_out' and description 'Add a phone number to the opt-out list (suppresses future messages)' indicate creation/modification of opt-out preferences.

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

POLICY

How to control add_opt_out

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 add_opt_out:

policy.json

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

add_opt_out 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.

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EXPLORE

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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 add_opt_out

What does the add_opt_out tool do? +

Add a phone number to the opt-out list (suppresses future messages). 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 add_opt_out? +

Register the Mcp Afip MCP server in PolicyLayer and add a rule for add_opt_out: 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 add_opt_out? +

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

Can I rate-limit add_opt_out? +

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

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

add_opt_out 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 →