STEP 1 - ALWAYS CALL THIS FIRST. Lists all calendars in the user
AI agents call list_calendars to retrieve information from Fastmail Calendar MCP Server 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 metadata without creating, modifying, deleting, or executing any operations. It is a read-only operation that gathers information needed before other calendar actions. The severity is low because calendar names alone pose minimal risk; the blast radius of misuse is limited to information disclosure of which calendars exist.
From the tool's definition Tool name 'list_calendars' and description 'Lists all calendars in the user' indicate a retrieval operation with no side effects.
Attacks that exploit this kind of access
STEP 1 - ALWAYS CALL THIS FIRST. Lists all calendars in the user. It is categorised as a Read tool in the Fastmail Calendar MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Fastmail Calendar MCP Server MCP server in PolicyLayer and add a rule for 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 Fastmail Calendar MCP Server. Nothing to install.
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 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 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.
list_calendars is provided by the Fastmail Calendar MCP Server MCP server (nova-3951/fastmail-calendar-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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