open_setup · nomos MCP Bridge MCP: Risk & Policy

WHAT IT DOES

What open_setup does on nomos MCP Bridge

AI agents invoke open_setup to trigger actions in nomos MCP Bridge. 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.

WHY IT NEEDS A POLICY

Why open_setup needs a policy

This tool executes an external operation (opening a browser window) rather than simply reading or writing data. The blast radius is low since it only opens a UI page for configuration, but it does trigger an observable side effect in the operating environment.

From the tool's definition 'Opens the nomos MCP Bridge setup page in the default browser' — triggers an external browser action

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

open_setup Rate-limited

open_setup 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.

View as policy code

policy.json

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

RATE-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 open_setup

What does the open_setup tool do? +

Opens the nomos MCP Bridge setup page in the default browser, where controllers can be added via a web form. It is categorised as a Execute tool in the nomos MCP Bridge MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on open_setup? +

Register the nomos MCP Bridge MCP server in PolicyLayer and add a rule for open_setup: 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 open_setup? +

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

Can I rate-limit open_setup? +

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

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

open_setup 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.