AI agents call list_calendars to retrieve information from Webcal without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves calendar metadata (the list of configured calendars) with no side effects, no data modification, and no operations triggered. It is a pure read operation aligned with the read-only nature of the server. Severity is low as it only exposes calendar names/identifiers without executing code or causing destructive actions.
From the tool's definition Tool name 'list_calendars' and server description states 'read-only MCP server' that enables 'calendar event retrieval'. The tool lists configured calendars without modifying any data.
Attacks that exploit this kind of access
List the configured calendars. It is categorised as a Read tool in the Webcal MCP Server, which means it retrieves data without modifying state.
Register the Webcal 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 Webcal. 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 Webcal MCP server (mnot/webcal-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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