block_host · Defined MCP: Risk & Policy

WHAT IT DOES

What block_host does on Defined

AI agents use block_host to create or update resources in Defined — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Defined environment.

WHY IT NEEDS A POLICY

Why block_host needs a policy

An AI agent can call block_host faster than any human can review — one bad instruction and it creates or modifies resources in Defined by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

block_host Rate-limited

block_host 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.

View as policy code

policy.json

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

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Defined, so you can run agents against it safely.

FAQ

Questions about block_host

What does the block_host tool do? +

Block a host, preventing it from communicating on the network. It is categorised as a Write tool in the Defined MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on block_host? +

Register the Defined MCP server in PolicyLayer and add a rule for block_host: 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 Defined. Nothing to install.

What risk level is block_host? +

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

Can I rate-limit block_host? +

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

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

block_host is provided by the Defined MCP server (quickvm/defined-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.