AI agents call market_hours 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 only retrieves static market status information. It does not create, modify, delete, execute external operations, or move money. Despite being on a financial trading server, the tool itself performs no financial transactions or irreversible actions. Classification as Read is appropriate, and severity is low because misuse poses minimal risk—an AI agent querying market hours cannot cause harm.
From the tool's definition Tool name 'market_hours' and description 'Gets current market hours and status' indicate a pure query operation that retrieves informational data about market operating times with no modifications, side effects, or external state changes.
Documented attack patterns abuse exactly the kind of access market_hours 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 market_hours:
{
"version": "1",
"default": "deny",
"tools": {
"market_hours": {}
}
}market_hours is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Gets current market hours and status. 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 market_hours: 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.
market_hours 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 market_hours 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 market_hours. 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.
market_hours 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.