set_cover · Lyceum MCP: Risk & Policy

WHAT IT DOES

What set_cover does on Lyceum

AI agents use set_cover to create or update resources in Lyceum — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Lyceum environment.

WHY IT NEEDS A POLICY

Why set_cover needs a policy

Setting a cover image modifies book metadata in the Calibre library. This is categorized as Write rather than Read (it changes data) or Destructive (the change is reversible—a new cover can be set). Severity is medium because unintended metadata changes could degrade library usability, but they do not delete data or cause financial harm.

From the tool's definition The tool name 'set_cover' and description 'Set a book' (incomplete, likely 'Set a book cover') indicates modifying metadata of an existing book record in the Calibre library. This is a reversible write operation that updates book properties.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_cover Rate-limited

set_cover 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_cover": {
      "limits": [
        {
          "counter": "set_cover_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Lyceum, so you can run agents against it safely.

FAQ

Questions about set_cover

What does the set_cover tool do? +

Set a book. It is categorised as a Write tool in the Lyceum MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_cover? +

Register the Lyceum MCP server in PolicyLayer and add a rule for set_cover: 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 Lyceum. Nothing to install.

What risk level is set_cover? +

set_cover is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit set_cover? +

Yes. Add a rate_limit block to the set_cover 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.

How do I block set_cover completely? +

Set action: deny in the PolicyLayer policy for set_cover. 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.

What MCP server provides set_cover? +

set_cover is provided by the Lyceum MCP server (matthewp/lyceum). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.