create_subaccount

THE RISK

Critical Risk

Why create_subaccount needs a policy

Creating a subaccount for payment splitting is a financial operation that establishes a new financial entity capable of receiving, routing, or splitting payments. On a payment protocol server, this could enable unauthorized fund diversion or fraudulent account structures if misused, warranting critical severity.

From the tool's definition 'Create a subaccount for payment splitting' — directly involves financial account creation within a payment protocol (AP2 — Google's Agent-to-Agent Payment Protocol)

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

POLICY

How to control create_subaccount

PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Ap2, and nothing reaches the server without passing your rules. This is the rule we recommend for create_subaccount:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "create_subaccount": {
      "deny_if": [
        {
          "conditions": [],
          "on_deny": "Requires human approval."
        }
      ]
    }
  }
}

Any call to create_subaccount is blocked until a human approves it. The rest of the server keeps working.

Create a free account and register Mcp Ap2 — 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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All 1300 Mcp Ap2 tools →

Financial tools on other servers

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Go deeper

Critical-risk tools in Mcp Ap2 → Every critical-risk tool this server exposes, in one view.
All critical-risk MCP tools → Every critical-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Human-in-the-loop → When a tool call should wait for a person — and when policy can decide alone.
Tool call approval → Approval gates on individual tool calls: auto-allow, prompt, or deny.
How to Add Spending Controls to Any MCP Agent →
Rate Limiting MCP Tool Calls: A Practical Guide →

FAQ

Questions about create_subaccount

What does the create_subaccount tool do? +

Create a subaccount for payment splitting. It is categorised as a Financial tool in the Mcp Ap2 MCP Server, which means it involves financial transactions. Block by default and require explicit approval.

How do I enforce a policy on create_subaccount? +

Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for create_subaccount: 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 Ap2. Nothing to install.

What risk level is create_subaccount? +

create_subaccount is a Financial tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.

Can I rate-limit create_subaccount? +

Yes. Add a rate_limit block to the create_subaccount 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_subaccount completely? +

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

create_subaccount is provided by the Mcp Ap2 MCP server (@codespar/mcp-ap2). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Mcp Ap2 tool call.

Start from Mcp Ap2, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →