AI agents call margin_calls 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 margin call data from the brokerage account without modifying, deleting, or executing any transactions. While margin calls relate to financial accounts, the tool itself only reads/displays information rather than moving money or creating obligations. The read nature and informational context place this in the Read category with low severity.
From the tool's definition Tool name 'margin_calls' with description 'Gets margin call information' indicates a retrieval operation. The verb 'Gets' explicitly describes a read-only query action with no modification of state.
Documented attack patterns abuse exactly the kind of access margin_calls 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 margin_calls:
{
"version": "1",
"default": "deny",
"tools": {
"margin_calls": {}
}
}margin_calls is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Gets margin call information. 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 margin_calls: 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.
margin_calls 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 margin_calls 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 margin_calls. 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.
margin_calls 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.
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152 Open Stocks MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.