AI agents call prepareCallHierarchy to retrieve information from Ts without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Even though prepareCallHierarchy only reads data, uncontrolled read access leaks sensitive information and racks up API costs — an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.
Attacks that exploit this kind of access
Returns the call hierarchy item(s) at a position — the entry point for call hierarchy queries. Returns the function/method name, kind, file location, and spans. It is categorised as a Read tool in the Ts MCP Server, which means it retrieves data without modifying state.
Register the Ts MCP server in PolicyLayer and add a rule for prepareCallHierarchy: 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 Ts. Nothing to install.
prepareCallHierarchy 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 prepareCallHierarchy 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 prepareCallHierarchy. 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.
prepareCallHierarchy is provided by the Ts MCP server (ts-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.