lemmy_list_communities

THE RISK

Low Risk

Why lemmy_list_communities needs a policy

The tool performs a read-only operation that lists communities. It retrieves information without creating, modifying, deleting, or executing any code. The 'Default scope' qualifier indicates standard read permissions without elevated access. This is a straightforward query operation with minimal blast radius if misused by an AI agent.

From the tool's definition Tool name is 'lemmy_list_communities' with description 'List communities. Default scope' - this retrieves/queries community data with no side effects.

Documented attack patterns abuse exactly the kind of access lemmy_list_communities gives an agent:

POLICY

How to control lemmy_list_communities

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 lemmy_list_communities:

policy.json

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

lemmy_list_communities is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Crow — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

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EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
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FAQ

Questions about lemmy_list_communities

What does the lemmy_list_communities tool do? +

List communities. Default scope. 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 lemmy_list_communities? +

Register the Crow MCP server in PolicyLayer and add a rule for lemmy_list_communities: 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 lemmy_list_communities? +

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

Can I rate-limit lemmy_list_communities? +

Yes. Add a rate_limit block to the lemmy_list_communities 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 lemmy_list_communities completely? +

Set action: deny in the PolicyLayer policy for lemmy_list_communities. 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 lemmy_list_communities? +

lemmy_list_communities 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.

Enforce policy on every Crow tool call.

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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