AI agents call price_history to retrieve information from Open Paper Trading MCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves historical price information, which is a read-only operation. It queries existing market data without creating, modifying, deleting, or executing any financial transactions. The paper trading context confirms the data is from real markets but used in a simulation environment where no actual funds or positions are at risk.
From the tool's definition Tool name 'price_history' and description 'Get historical price data for a stock' indicate pure data retrieval with no modifications, side effects, or external state changes.
Documented attack patterns abuse exactly the kind of access price_history gives an agent:
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 price_history:
{
"version": "1",
"default": "deny",
"tools": {
"price_history": {}
}
}price_history is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get historical price data for a stock. It is categorised as a Read tool in the Open Paper Trading MCP MCP Server, which means it retrieves data without modifying state.
Register the Open Paper Trading MCP server in PolicyLayer and add a rule for price_history: 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.
price_history is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the price_history 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.
Set action: deny in the PolicyLayer policy for price_history. 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.
price_history 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.
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.
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44 Open Paper Trading MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.