AI agents use create-comment to create or update resources in Liveblocks — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Liveblocks environment.
Creating a comment is a reversible write operation that adds data to the system. It is not destructive (comments can be deleted via the sibling delete-comment tool), does not execute arbitrary code, and has no financial impact.
From the tool's definition Tool name 'create-comment' and description 'Create a Liveblocks comment' indicate the tool creates new data in the Liveblocks system. The requirement to 'Always ask for a userId' confirms it modifies state by adding a comment tied to a user identity.
Documented attack patterns abuse exactly the kind of access create-comment gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Liveblocks, and nothing reaches the server without passing your rules. This is the rule we recommend for create-comment:
{
"version": "1",
"default": "deny",
"tools": {
"create-comment": {
"limits": [
{
"counter": "create-comment_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}create-comment 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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Create a Liveblocks comment. Always ask for a userId. It is categorised as a Write tool in the Liveblocks MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Liveblocks MCP server in PolicyLayer and add a rule for create-comment: 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 Liveblocks. Nothing to install.
create-comment 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 create-comment 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 create-comment. 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.
create-comment is provided by the Liveblocks MCP server (liveblocks/liveblocks-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Liveblocks, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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39 Liveblocks tools catalogued and risk-classified — across an index of 43,000+ MCP servers.