AI agents call websocket_list_rooms to retrieve information from Excalidraw without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool merely enumerates existing resources (active WebSocket rooms and their subscribers) with no side effects, reversible actions, code execution, deletions, or financial operations. It is a pure read/query operation with minimal blast radius if misused—an AI agent listing rooms gains visibility but cannot manipulate diagrams, delete data, or trigger external effects.
From the tool's definition Tool name 'websocket_list_rooms' and description 'List all active rooms and their subscribers' indicate a query operation that retrieves state information without modifying or executing anything.
Documented attack patterns abuse exactly the kind of access websocket_list_rooms gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Excalidraw, and nothing reaches the server without passing your rules. This is the rule we recommend for websocket_list_rooms:
{
"version": "1",
"default": "deny",
"tools": {
"websocket_list_rooms": {}
}
}websocket_list_rooms is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List all active rooms and their subscribers. It is categorised as a Read tool in the Excalidraw MCP Server, which means it retrieves data without modifying state.
Register the Excalidraw MCP server in PolicyLayer and add a rule for websocket_list_rooms: 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 Excalidraw. Nothing to install.
websocket_list_rooms is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the websocket_list_rooms 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 websocket_list_rooms. 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.
websocket_list_rooms is provided by the Excalidraw MCP server (lesleslie/excalidraw-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Excalidraw, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
17 Excalidraw tools catalogued and risk-classified — across an index of 43,000+ MCP servers.