AI agents call is_market_open to retrieve information from Paper MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a simple status check of market conditions. It retrieves data (whether a market is open) with no side effects, no code execution, and no financial impact. Despite being on a trading platform server, this specific tool only reads market information and does not create orders, modify accounts, or commit financial obligations. It is purely informational.
From the tool's definition Tool name 'is_market_open' and description 'Check if market is open for a symbol' indicate a query operation that retrieves market status information without modifying, executing, or affecting financial positions.
Documented attack patterns abuse exactly the kind of access is_market_open gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Paper MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for is_market_open:
{
"version": "1",
"default": "deny",
"tools": {
"is_market_open": {}
}
}is_market_open is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Check if market is open for a symbol. It is categorised as a Read tool in the Paper MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Paper MCP Server MCP server in PolicyLayer and add a rule for is_market_open: 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 Paper MCP Server. Nothing to install.
is_market_open 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 is_market_open 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 is_market_open. 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.
is_market_open is provided by the Paper MCP Server MCP server (paperinvest/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Paper MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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23 Paper MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.