AI agents call get_availability to retrieve information from Fantastical MCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
get_availability queries calendar data to display free and busy periods. This is a read-only operation that retrieves existing information without creating, modifying, or deleting calendar events or other data. It has no side effects and poses minimal security risk if an AI agent invokes it with various dates.
From the tool's definition Tool name and description indicate retrieval of availability/free-busy information: 'Show free/busy time slots for a specific date.' No modification, deletion, or execution of external operations occurs.
Documented attack patterns abuse exactly the kind of access get_availability gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Fantastical MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for get_availability:
{
"version": "1",
"default": "deny",
"tools": {
"get_availability": {}
}
}get_availability is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Show free/busy time slots for a specific date. It is categorised as a Read tool in the Fantastical MCP MCP Server, which means it retrieves data without modifying state.
Register the Fantastical MCP server in PolicyLayer and add a rule for get_availability: 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 Fantastical MCP. Nothing to install.
get_availability 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 get_availability 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 get_availability. 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.
get_availability is provided by the Fantastical MCP server (jaydenk/fantastical-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Fantastical 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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16 Fantastical MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.