buy_stock_limit

THE RISK

Critical Risk

Why buy_stock_limit needs a policy

This tool places a buy order for stocks, which constitutes a financial transaction (committing capital to purchase securities). Even though it is described as 'paper trading' (simulated), the tool is classified as Financial because it simulates financial obligations and is part of a trading system.

From the tool's definition Place a limit buy order for stocks

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

POLICY

How to control buy_stock_limit

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

policy.json

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

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

Create a free account and register Open Paper Trading MCP — 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

Related tools and policies

More Open Paper Trading MCP tools

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All 44 Open Paper Trading MCP tools →

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Go deeper

Critical-risk tools in Open Paper Trading MCP → 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 buy_stock_limit

What does the buy_stock_limit tool do? +

Place a limit buy order for stocks. It is categorised as a Financial tool in the Open Paper Trading MCP MCP Server, which means it involves financial transactions. Block by default and require explicit approval.

How do I enforce a policy on buy_stock_limit? +

Register the Open Paper Trading MCP server in PolicyLayer and add a rule for buy_stock_limit: 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 Open Paper Trading MCP. Nothing to install.

What risk level is buy_stock_limit? +

buy_stock_limit 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 buy_stock_limit? +

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

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

buy_stock_limit is provided by the Open Paper Trading MCP server (open-agent-tools/open-paper-trading-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Open Paper Trading MCP tool call.

Start from Open Paper Trading MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →