notebook_add_cell

THE RISK

Medium Risk

Why notebook_add_cell needs a policy

This tool creates new cells in a notebook, which is a reversible write operation. It does not execute code (no Execute), delete data (no Destructive), or affect financials. The severity is medium because adding cells to a notebook could inject malicious code or disrupt workflow, but the impact is localized to the notebook file and can be undone by deleting the cell.

From the tool's definition Tool description states 'Adds a new code or markdown cell' — a create operation that modifies notebook structure. The tool name includes 'add', and the description uses 'Adds', both indicating data creation/modification without deletion.

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

POLICY

How to control notebook_add_cell

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_add_cell:

policy.json

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

notebook_add_cell 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 →

Free to start. No card required.

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_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 Write notebook_duplicate_cell Duplicates a cell multiple times (default: once)

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_add_cell

What does the notebook_add_cell tool do? +

Adds a new code or markdown cell after a specified index. 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_add_cell? +

Register the Claude Code Notebook MCP server in PolicyLayer and add a rule for notebook_add_cell: 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_add_cell? +

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

Can I rate-limit notebook_add_cell? +

Yes. Add a rate_limit block to the notebook_add_cell 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_add_cell completely? +

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

notebook_add_cell 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 →