List rooms the authenticated user is in, with a name hint for each.
AI agents call matrix_joined_rooms to retrieve information from Crow without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves information about the authenticated user's Matrix room memberships. It performs a read-only query of existing data without creating, modifying, deleting, or executing anything. The blast radius of misuse is minimal—an attacker could enumerate rooms the user participates in, but cannot manipulate data or trigger external actions. This is a standard Read category tool.
From the tool's definition Tool description states 'List rooms' which is a retrieval operation with no side effects. The verb 'List' and the output-only nature (name hints for rooms) indicate a query operation.
Documented attack patterns abuse exactly the kind of access matrix_joined_rooms gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Crow, and nothing reaches the server without passing your rules. This is the rule we recommend for matrix_joined_rooms:
{
"version": "1",
"default": "deny",
"tools": {
"matrix_joined_rooms": {}
}
}matrix_joined_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 rooms the authenticated user is in, with a name hint for each. It is categorised as a Read tool in the Crow MCP Server, which means it retrieves data without modifying state.
Register the Crow MCP server in PolicyLayer and add a rule for matrix_joined_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 Crow. Nothing to install.
matrix_joined_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 matrix_joined_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 matrix_joined_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.
matrix_joined_rooms is provided by the Crow MCP server (kh0pper/crow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Crow, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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576 Crow tools catalogued and risk-classified — across an index of 43,000+ MCP servers.