place_market_order

THE RISK

Critical Risk

Why place_market_order needs a policy

This tool directly executes financial transactions by placing market orders to buy or sell securities via the Alpaca trading API. Market orders execute immediately at current market prices and commit real financial obligations. Misuse could result in significant financial losses through unintended trades, making this critical severity.

From the tool's definition "Place a market order to buy or sell a stock"

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

POLICY

How to control place_market_order

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

policy.json

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

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

Create a free account and register Alpaca Trading MCP Server — 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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Free to start. No card required.

EXPLORE

Related tools and policies

More Alpaca Trading MCP Server tools

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All 8 Alpaca Trading MCP Server tools →

Financial tools on other servers

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Go deeper

Critical-risk tools in Alpaca Trading MCP Server → 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 place_market_order

What does the place_market_order tool do? +

Place a market order to buy or sell a stock. It is categorised as a Financial tool in the Alpaca Trading MCP Server MCP Server, which means it involves financial transactions. Block by default and require explicit approval.

How do I enforce a policy on place_market_order? +

Register the Alpaca Trading MCP Server MCP server in PolicyLayer and add a rule for place_market_order: 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 Alpaca Trading MCP Server. Nothing to install.

What risk level is place_market_order? +

place_market_order 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 place_market_order? +

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

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

place_market_order is provided by the Alpaca Trading MCP Server MCP server (laukikk/alpaca-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Alpaca Trading MCP Server tool call.

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

CHECK YOUR STACK →