update_amount

THE RISK

Critical Risk

Why update_amount needs a policy

This tool directly modifies the financial authorization amount of a payment transaction. Even though it operates on unsettled payments (making it technically reversible in some contexts), it commits financial obligations by altering the authorized charge amount, placing it firmly in the Financial category.

From the tool's definition Update the authorized amount of an unsettled payment (common in tips / hotel incidentals)

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

POLICY

How to control update_amount

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 update_amount:

policy.json

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

Any call to update_amount 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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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 update_amount

What does the update_amount tool do? +

Update the authorized amount of an unsettled payment (common in tips / hotel incidentals). 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 update_amount? +

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

update_amount 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 update_amount? +

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

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

update_amount 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.

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