crow_send_message

THE RISK

Medium Risk

Why crow_send_message needs a policy

This tool sends messages to an external network. While it creates data (Write), the key concern is that messages are irreversible — however, this is not deletion/overwriting of existing data, it's creation of permanent external communications. The most accurate category is Write.

From the tool's definition 'Send an encrypted message via the Nostr network. Messages cannot be retracted once sent.'

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

POLICY

How to control crow_send_message

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 crow_send_message:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "crow_send_message": {
      "limits": [
        {
          "counter": "crow_send_message_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

crow_send_message stays usable, but capped — an agent stuck in a loop can't make hundreds of changes 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.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about crow_send_message

What does the crow_send_message tool do? +

Send an encrypted message via the Nostr network. Messages cannot be retracted once sent. It is categorised as a Write tool in the Crow MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on crow_send_message? +

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

crow_send_message is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit crow_send_message? +

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

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

crow_send_message 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.

CHECK YOUR STACK →