sign_buy_url

THE RISK

Critical Risk

Why sign_buy_url needs a policy

MoonPay is a cryptocurrency purchase service. Signing and generating a buy widget URL initiates or facilitates a financial transaction (crypto purchase). While signing alone does not transfer funds, it creates an authenticated URL that directly enables a financial transaction, placing it in the Financial category. Misuse could redirect users to purchase crypto under attacker-controlled parameters.

From the tool's definition sign a MoonPay buy widget URL (buy.moonpay.com). Returns a ready-to-redirect URL with the merchant

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

POLICY

How to control sign_buy_url

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 sign_buy_url:

policy.json

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

Any call to sign_buy_url 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.

GATE THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Mcp Ap2 tools

Financial authorize_transaction Authorize a transaction (reserve funds without capturing) via Braintree GraphQL authorizeP Financial block_card Block a card temporarily (reversible). Use for lost-card or fraud-suspected flows. Card st Financial cancel_bill Cancel a pending bill Financial cancel_collection Cancel a scheduled collection request Financial cancel_credit Cancel an authorized-but-uncaptured credit payment. Financial cancel_debit Cancel a debit-card payment by Getnet payment_id. Financial cancel_invoice Cancel/void an authorized invoice (FECancel — limited to certain types/conditions) Financial cancel_order Cancel an order, optionally restocking and refunding

All 1300 Mcp Ap2 tools →

Financial tools on other servers

0xarchive web3_subscribe Math MCP Server financial_calculator MCP Kling generate_video MCP Uber Server uber_request_ride

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 sign_buy_url

What does the sign_buy_url tool do? +

Build and HMAC-SHA256 sign a MoonPay buy widget URL (buy.moonpay.com). Returns a ready-to-redirect URL with the merchant. 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 sign_buy_url? +

Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for sign_buy_url: 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 sign_buy_url? +

sign_buy_url 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 sign_buy_url? +

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

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

sign_buy_url 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 →