Read/write structured notes for a long document in a JSON file (_notes.json in book_dir). Useful for tracking glossaries, chapter summaries, TODO lists, inconsistencies found while iterating through a long text. Operations: get (read the whole JSON or one key), set (overwrite a key), append (push...
AI agents use book_note to create or update resources in Self-hosted MCP server for Claude — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Self-hosted MCP server for Claude environment.
While the tool includes read operations ('get'), the primary purpose is data modification through 'set' and 'append' operations on a structured JSON notes file. This is Write category—reversible changes to a local data file (you can edit or delete the notes). It is not Destructive because JSON records can be recovered or modified afterward.
From the tool's definition Tool description explicitly states 'Read/write' and includes operations 'set (overwrite a key)' and 'append (push to a list under a key)' which modify a local JSON file (_notes.json). The 'get' operation is read-only but the write capability is primary.
Attacks that exploit this kind of access
Read/write structured notes for a long document in a JSON file (_notes.json in book_dir). Useful for tracking glossaries, chapter summaries, TODO lists, inconsistencies found while iterating through a long text. Operations: get (read the whole JSON or one key), set (overwrite a key), append (push to a list under a key). Keys support dot-notation for nesting (e.g. It is categorised as a Write tool in the Self-hosted MCP server for Claude MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Self-hosted MCP server for Claude MCP server in PolicyLayer and add a rule for book_note: 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 Self-hosted MCP server for Claude. Nothing to install.
book_note is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the book_note 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 book_note. 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.
book_note is provided by the Self-hosted MCP server for Claude MCP server (leszczynskikarol/mcp-server). 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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