AI agents call top_movers_sp500 to retrieve information from Open Stocks 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 market data about S&P 500 price movements. It has no side effects, does not modify account state, does not execute trades, and does not commit financial transactions. It is a read-only query of public market information.
From the tool's definition Tool name 'top_movers_sp500' and description 'Gets top S&P 500 movers for the day' indicate data retrieval with no modification, deletion, or execution of trades. The action is purely informational—querying market data.
Documented attack patterns abuse exactly the kind of access top_movers_sp500 gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Open Stocks MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for top_movers_sp500:
{
"version": "1",
"default": "deny",
"tools": {
"top_movers_sp500": {}
}
}top_movers_sp500 is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Gets top S&P 500 movers for the day. It is categorised as a Read tool in the Open Stocks MCP MCP Server, which means it retrieves data without modifying state.
Register the Open Stocks MCP server in PolicyLayer and add a rule for top_movers_sp500: 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 Stocks MCP. Nothing to install.
top_movers_sp500 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 top_movers_sp500 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 top_movers_sp500. 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.
top_movers_sp500 is provided by the Open Stocks MCP server (open-agent-tools/open-stocks-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Open Stocks MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
152 Open Stocks MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.