write_file_metadata

Write metadata directly into the ebook file (EPUB, MOBI, etc.).

SERVERCalibre SOURCE2b3pro/calibre-mcp

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade B, identity unverified Pull the record →

This record as markdown: /tools/2b3pro-calibre-mcp/write-file-metadata.md

WHAT IT DOES

What write_file_metadata does on Calibre

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

RISK

Why write_file_metadata is rated Medium

This tool creates or modifies ebook metadata within file structures. While not destructive (changes are reversible by overwriting metadata again) and not financial, it clearly performs a Write operation that alters persisted data.

From the tool's definition Tool description explicitly states 'Write metadata directly into the ebook file (EPUB, MOBI, etc.)' — the 'Write' verb combined with 'directly into the ebook file' indicates data modification.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs write_file_metadata safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Calibre, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For write_file_metadata, this is the rule to start with:

write_file_metadata Rate-limited

write_file_metadata 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": {
    "write_file_metadata": {
      "limits": [
        {
          "counter": "write_file_metadata_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Calibre, apply this rule, and every write_file_metadata call is checked against it from then on.

FAQ

Questions about write_file_metadata

What does the write_file_metadata tool do? +

Write metadata directly into the ebook file (EPUB, MOBI, etc.). It is categorised as a Write tool in the Calibre MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on write_file_metadata? +

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

What risk level is write_file_metadata? +

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

Can I rate-limit write_file_metadata? +

Yes. Add a rate_limit block to the write_file_metadata 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 write_file_metadata completely? +

Set action: deny in the PolicyLayer policy for write_file_metadata. 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 write_file_metadata? +

write_file_metadata is provided by the Calibre MCP server (2b3pro/calibre-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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