Broadcast a test event to a channel (development only).
AI agents invoke websocket_broadcast_test_event to trigger actions in Excalidraw. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool executes a broadcast action over a WebSocket channel. While labeled 'development only', it triggers side effects in external systems (connected clients receive the event). It's not purely read, and the effects depend on what event/channel is specified. Classified as Execute since it initiates an operation with real-time external effects, though severity is medium given the development-only scope.
From the tool's definition 'Broadcast a test event to a channel' — triggers an external operation (WebSocket broadcast) whose effects depend on arguments
Documented attack patterns abuse exactly the kind of access websocket_broadcast_test_event 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_broadcast_test_event:
{
"version": "1",
"default": "deny",
"tools": {
"websocket_broadcast_test_event": {
"limits": [
{
"counter": "websocket_broadcast_test_event_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}websocket_broadcast_test_event stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
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Broadcast a test event to a channel (development only). It is categorised as a Execute tool in the Excalidraw MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Excalidraw MCP server in PolicyLayer and add a rule for websocket_broadcast_test_event: 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_broadcast_test_event is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the websocket_broadcast_test_event 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_broadcast_test_event. 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_broadcast_test_event 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.