List all CalDAV calendars for the authenticated Fastmail account.
AI agents call calendar_list_calendars to retrieve information from Pyfastmail without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries and returns calendar data without creating, modifying, deleting, or executing operations. It is a straightforward enumeration/listing function that retrieves existing calendar metadata. While it accesses personal data (calendars), the blast radius of misuse is limited to information disclosure rather than destructive or operational harm.
From the tool's definition Tool name is 'calendar_list_calendars' and description states 'List all CalDAV calendars' — a retrieval operation with no modification or side effects.
Attacks that exploit this kind of access
List all CalDAV calendars for the authenticated Fastmail account. It is categorised as a Read tool in the Pyfastmail MCP Server, which means it retrieves data without modifying state.
Register the Pyfastmail MCP server in PolicyLayer and add a rule for calendar_list_calendars: 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 Pyfastmail. Nothing to install.
calendar_list_calendars 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 calendar_list_calendars 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 calendar_list_calendars. 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.
calendar_list_calendars is provided by the Pyfastmail MCP server (pjosols/pyfastmail-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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