matrix_join_room

Join a room by ID or alias. If the room lives on another server, Dendrite federates the join (may take several seconds). Rate-limited: 30/hour.

SERVERCrow SOURCEkh0pper/crow

Low RISK CLASS

Category Read

Parameters 00 required

Recommended Allowedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/kh0pper-crow/matrix-join-room.md

WHAT IT DOES

What matrix_join_room does on Crow

AI agents call matrix_join_room to retrieve information from Crow without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.

RISK

Why matrix_join_room is rated Low

Even though matrix_join_room only reads data, uncontrolled read access leaks sensitive information and racks up API costs: an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs matrix_join_room safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Crow, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For matrix_join_room, this is the rule to start with:

matrix_join_room Allowed

matrix_join_room is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "matrix_join_room": {}
  }
}

ALLOW ONLY THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Crow, apply this rule, and every matrix_join_room call is checked against it from then on.

FAQ

Questions about matrix_join_room

What does the matrix_join_room tool do? +

Join a room by ID or alias. If the room lives on another server, Dendrite federates the join (may take several seconds). Rate-limited: 30/hour. It is categorised as a Read tool in the Crow MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on matrix_join_room? +

Register the Crow MCP server in PolicyLayer and add a rule for matrix_join_room: 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.

What risk level is matrix_join_room? +

matrix_join_room is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit matrix_join_room? +

Yes. Add a rate_limit block to the matrix_join_room 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.

How do I block matrix_join_room completely? +

Set action: deny in the PolicyLayer policy for matrix_join_room. 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.

What MCP server provides matrix_join_room? +

matrix_join_room 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.

KEEP EXPLORING

More on Crow, and thousands of servers like it.

This server

All 587 Crow tools →

Across the catalogue

The MCP Attack Database →

Guides

Roll out MCP under one policy →Data exfiltration →MCP token cost →