lemmy_block_instance

THE RISK

High Risk

Why lemmy_block_instance needs a policy

This tool triggers an external operation that affects federation with an entire remote instance — cutting off all content fetching and federation. While it has a confirmation queue (reducing blast radius), it has broad network-level effects. It's not purely destructive (reversible block), not financial, but it executes a significant administrative action with wide impact.

From the tool's definition Block an entire remote instance (no federation, no fetched content). Admin-only; QUEUED — requires operator confirmation in the Nest panel.

Risk signalsBulk/mass operation — affects multiple targets · Admin/system-level operation

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

POLICY

How to control lemmy_block_instance

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_block_instance:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "lemmy_block_instance": {
      "limits": [
        {
          "counter": "lemmy_block_instance_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

lemmy_block_instance 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.

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.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

High-risk tools in Crow → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
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FAQ

Questions about lemmy_block_instance

What does the lemmy_block_instance tool do? +

Block an entire remote instance (no federation, no fetched content). Admin-only; QUEUED — requires operator confirmation in the Nest panel. It is categorised as a Execute tool in the Crow MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on lemmy_block_instance? +

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

lemmy_block_instance is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit lemmy_block_instance? +

Yes. Add a rate_limit block to the lemmy_block_instance 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_block_instance completely? +

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

lemmy_block_instance 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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