notebook_merge_cells

THE RISK

Medium Risk

Why notebook_merge_cells needs a policy

Merging cells modifies notebook structure and content by combining two cells into one, which is a write operation. It is not destructive because the data is not deleted (both cells' contents are preserved in the merged result) and is reversible.

From the tool's definition Tool name and description indicate 'merges a cell with the cell immediately following it' — a modification operation that combines cell contents.

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

POLICY

How to control notebook_merge_cells

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

policy.json

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

notebook_merge_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 Claude Code Notebook MCP — 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 →

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EXPLORE

Related tools and policies

More Claude Code Notebook MCP tools

Destructive notebook_delete Deletes an existing notebook file Destructive notebook_delete_cell Deletes a specific cell Write notebook_clear_all_outputs Clears outputs and execution counts for all code cells Write notebook_clear_cell_outputs Clears the outputs and execution count of a specific cell Write notebook_add_cell Adds a new code or markdown cell after a specified index Write notebook_bulk_add_cells Adds multiple cells to a notebook in a single operation Write notebook_change_cell_type Changes a cell Write notebook_create Creates a new, empty notebook file

All 29 Claude Code Notebook MCP tools →

Write tools on other servers

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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 notebook_merge_cells

What does the notebook_merge_cells tool do? +

Merges a cell with the cell immediately following it. It is categorised as a Write tool in the Claude Code Notebook MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on notebook_merge_cells? +

Register the Claude Code Notebook MCP server in PolicyLayer and add a rule for notebook_merge_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 Claude Code Notebook MCP. Nothing to install.

What risk level is notebook_merge_cells? +

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

Can I rate-limit notebook_merge_cells? +

Yes. Add a rate_limit block to the notebook_merge_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 notebook_merge_cells completely? +

Set action: deny in the PolicyLayer policy for notebook_merge_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 notebook_merge_cells? +

notebook_merge_cells is provided by the Claude Code Notebook MCP server (mstampfer/claude-code-notebook-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Claude Code Notebook MCP tool call.

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

CHECK YOUR STACK →