// MCP TOOL REFERENCE

fw_block_domain

Instance-wide block of a remote domain (all actors/libraries from that domain become unreachable). QUEUED — does not apply until an operator confirms in the Nest panel within 72 hours.

ServerCrow
CategoryExecute

How to control fw_block_domain ↓

WHAT IT DOES

What fw_block_domain does on Crow

AI agents invoke fw_block_domain to trigger actions in Crow. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

THE RISK

High Risk

Why fw_block_domain needs a policy

This tool triggers a network-level blocking action that makes an entire remote domain unreachable instance-wide. While it is queued and requires operator confirmation within 72 hours (reducing immediacy), the action itself — when confirmed — is an operational change that affects external connectivity for all users/actors on the instance.

From the tool's definition Instance-wide block of a remote domain (all actors/libraries from that domain become unreachable)

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

POLICY

How to control fw_block_domain

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 fw_block_domain:

policy.json

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

fw_block_domain 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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FAQ

Questions about fw_block_domain

What does the fw_block_domain tool do? +

Instance-wide block of a remote domain (all actors/libraries from that domain become unreachable). QUEUED — does not apply until an operator confirms in the Nest panel within 72 hours. 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 fw_block_domain? +

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

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

Can I rate-limit fw_block_domain? +

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

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

fw_block_domain 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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