add_controller · nomos MCP Bridge MCP: Risk & Policy

WHAT IT DOES

What add_controller does on nomos MCP Bridge

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

WHY IT NEEDS A POLICY

Why add_controller needs a policy

This is a Write operation (creates/registers new data) rather than Read. However, severity is elevated to 'high' rather than typical Write 'medium' because: (1) registering a new smart home controller grants it system access and potential control over physical devices; (2) if a malicious or misconfigured controller is registered, it could impact home automation security; (3) controller registration affects system…

From the tool's definition Tool name 'add_controller' and description 'Registers a new nomos controller' indicates data creation/modification. Registering a controller adds a new entry to the system's configuration, reversibly modifying system state.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_controller Rate-limited

add_controller 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": {
    "add_controller": {
      "limits": [
        {
          "counter": "add_controller_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 nomos MCP Bridge, so you can run agents against it safely.

FAQ

Questions about add_controller

What does the add_controller tool do? +

Registers a new nomos controller. If this is the first controller, it is automatically selected. It is categorised as a Write tool in the nomos MCP Bridge MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_controller? +

Register the nomos MCP Bridge MCP server in PolicyLayer and add a rule for add_controller: 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 nomos MCP Bridge. Nothing to install.

What risk level is add_controller? +

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

Can I rate-limit add_controller? +

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

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

add_controller is provided by the nomos MCP Bridge MCP server (nomos-system/nomos-mcp-bridge). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.