AI agents use append-block-children to create or update resources in Notion MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Notion MCP Server environment.
This tool writes new data to Notion by appending blocks to a parent, which is a reversible content creation operation. It modifies existing pages/blocks but does not delete or overwrite existing content. Misuse could pollute Notion pages with unwanted content, hence medium severity.
From the tool's definition 'Append blocks to a parent block' — creates new content by adding blocks to an existing parent block
Documented attack patterns abuse exactly the kind of access append-block-children gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Notion MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for append-block-children:
{
"version": "1",
"default": "deny",
"tools": {
"append-block-children": {
"limits": [
{
"counter": "append-block-children_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}append-block-children 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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Append blocks to a parent block. It is categorised as a Write tool in the Notion MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Notion MCP Server MCP server in PolicyLayer and add a rule for append-block-children: 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 Notion MCP Server. Nothing to install.
append-block-children 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 append-block-children 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 append-block-children. 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.
append-block-children is provided by the Notion MCP Server MCP server (sjotie/notionmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Notion MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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12 Notion MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.