AI agents call get_user_book to retrieve information from Hardcover without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries and retrieves existing data from the user's library (status, rating, read count) without creating, modifying, deleting, or executing anything. It is a straightforward read operation with minimal risk even if misused by an agent.
From the tool's definition Tool name 'get_user_book' and description 'Get your library entry for a book: status, rating, reads' indicate retrieval of user book data with no modification or side effects.
Attacks that exploit this kind of access
Get your library entry for a book: status, rating, reads. It is categorised as a Read tool in the Hardcover MCP Server, which means it retrieves data without modifying state.
Register the Hardcover MCP server in PolicyLayer and add a rule for get_user_book: 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 Hardcover. Nothing to install.
get_user_book 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_user_book 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_user_book. 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_user_book is provided by the Hardcover MCP server (kristianedlund/hardcover-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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