qr_code · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What qr_code does on Nexus Core

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

WHY IT NEEDS A POLICY

Why qr_code needs a policy

This tool creates a new file (PNG image) on disk. It generates data and writes it to a path constrained within ALLOWED_ROOTS. It does not execute code, delete data, or involve finances. The blast radius is low since it only creates image files within a sandboxed directory.

From the tool's definition Generate a QR code PNG. output_path must resolve inside ALLOWED_ROOTS.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

qr_code Rate-limited

qr_code 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": {
    "qr_code": {
      "limits": [
        {
          "counter": "qr_code_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about qr_code

What does the qr_code tool do? +

Generate a QR code PNG. output_path must resolve inside ALLOWED_ROOTS. It is categorised as a Write tool in the Nexus Core MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on qr_code? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for qr_code: 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 Nexus Core. Nothing to install.

What risk level is qr_code? +

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

Can I rate-limit qr_code? +

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

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

qr_code is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

// THE FULL RECORD

qr_code is one line of Nexus Core's registry record.

The record carries the whole server: verified identity, auth posture, risk grade, every tool classified, recommended policy — re-checked continuously.

Teams ship this data inside their own products. See what a licence covers →