AI agents use excel_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.
This tool modifies spreadsheet structure by unmerging previously merged cells. It is a Write operation because it creates or modifies data/formatting reversibly. Severity is medium because misuse could corrupt game configuration layouts or spreadsheet organization, affecting data readability and structure, but the change is not destructive (can be undone by re-merging).
From the tool's definition Tool name 'excel_unmerge_cells' and description '取消合并单元格' (unmerge cells in Chinese) indicate modification of cell formatting/structure in Excel files. The action is reversible (cells can be merged again).
Documented attack patterns abuse exactly the kind of access excel_unmerge_cells gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Excel, and nothing reaches the server without passing your rules. This is the rule we recommend for excel_unmerge_cells:
{
"version": "1",
"default": "deny",
"tools": {
"excel_unmerge_cells": {
"limits": [
{
"counter": "excel_unmerge_cells_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}excel_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.
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取消合并单元格. 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.
Register the Excel MCP server in PolicyLayer and add a rule for excel_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.
excel_unmerge_cells 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 excel_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.
Set action: deny in the PolicyLayer policy for excel_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.
excel_unmerge_cells is provided by the Excel MCP server (tangentdomain/excel-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Excel, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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36 Excel tools catalogued and risk-classified — across an index of 43,000+ MCP servers.