unmerge_cells · Excel MCP: Risk & Policy

WHAT IT DOES

What unmerge_cells does on Excel

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

WHY IT NEEDS A POLICY

Why unmerge_cells needs a policy

Unmerging cells is a reversible modification to Excel formatting and structure. It changes how cells are organized but does not delete data, execute code, or create financial/destructive effects. This is a standard Write operation typical of spreadsheet editing tools. The severity is low because the change is easily reversible and has minimal business impact.

From the tool's definition Tool name 'unmerge_cells' and description 'Unmerge previously merged cells' indicate a cell formatting operation that modifies spreadsheet structure reversibly.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

unmerge_cells Rate-limited

unmerge_cells 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": {
    "unmerge_cells": {
      "limits": [
        {
          "counter": "unmerge_cells_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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

FAQ

Questions about unmerge_cells

What does the unmerge_cells tool do? +

Unmerge previously merged cells. It is categorised as a Write tool in the Excel MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on unmerge_cells? +

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

What risk level is unmerge_cells? +

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

Can I rate-limit unmerge_cells? +

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

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

unmerge_cells is provided by the Excel MCP server (shmaxi/excel-mcp-server-node). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.