AI agents use add-comment-reaction 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.
This tool creates or modifies data (adds a reaction to an existing comment) in a reversible manner. It does not execute arbitrary code, delete data irreversibly, move money, or merely read. The blast radius is limited to comment reactions within Liveblocks' collaboration system.
From the tool's definition Tool name 'add-comment-reaction' and description 'Add a reaction to a Liveblocks comment' indicate the tool modifies comment data by attaching a reaction, which is a reversible creation of new data.
Documented attack patterns abuse exactly the kind of access add-comment-reaction 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 add-comment-reaction:
{
"version": "1",
"default": "deny",
"tools": {
"add-comment-reaction": {
"limits": [
{
"counter": "add-comment-reaction_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add-comment-reaction 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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Add a reaction to a Liveblocks comment. 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 add-comment-reaction: 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.
add-comment-reaction 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 add-comment-reaction 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 add-comment-reaction. 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.
add-comment-reaction 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.