AI agents use open_book to create or update resources in InDesign UXP MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your InDesign UXP MCP Server environment.
Opening a book loads it into the application session, creating a new active state and potentially modifying file metadata or lock files. It is reversible (the book can be closed), so it does not qualify as Destructive. It does not purely read data without side effects — opening a file in InDesign typically acquires a lock and modifies session state, placing it in Write territory rather than pure Read.
From the tool's definition Open an existing InDesign book
Documented attack patterns abuse exactly the kind of access open_book gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and InDesign UXP MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for open_book:
{
"version": "1",
"default": "deny",
"tools": {
"open_book": {
"limits": [
{
"counter": "open_book_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}open_book stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Open an existing InDesign book. It is categorised as a Write tool in the InDesign UXP MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the InDesign UXP MCP Server MCP server in PolicyLayer and add a rule for open_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 InDesign UXP MCP Server. Nothing to install.
open_book 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 open_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 open_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.
open_book is provided by the InDesign UXP MCP Server MCP server (theloniuser/indesign-uxp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 135 InDesign UXP MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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135 InDesign UXP MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.