format_cells

THE RISK

Medium Risk

Why format_cells needs a policy

This tool modifies cell appearance (fonts, colors, borders, alignment) in Excel files. It creates or modifies data reversibly — formatting changes can be undone or reapplied. It does not delete data, execute code, or involve financial transactions. Severity is low because formatting changes have minimal blast radius; they affect visual presentation only, not underlying data values.

From the tool's definition Apply formatting to Excel cells (fonts, colors, borders, alignment)

Documented attack patterns abuse exactly the kind of access format_cells gives an agent:

POLICY

How to control format_cells

PolicyLayer is an MCP gateway — it sits between your AI agents and Excel MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for format_cells:

policy.json

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

format_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.

Create a free account and register Excel MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about format_cells

What does the format_cells tool do? +

Apply formatting to Excel cells (fonts, colors, borders, alignment). It is categorised as a Write tool in the Excel MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on format_cells? +

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

What risk level is format_cells? +

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

Can I rate-limit format_cells? +

Yes. Add a rate_limit block to the format_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 format_cells completely? +

Set action: deny in the PolicyLayer policy for format_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 format_cells? +

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

Enforce policy on every Excel MCP Server tool call.

Start from Excel MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →