previous_app · Ulanzi MCP: Risk & Policy

WHAT IT DOES

What previous_app does on Ulanzi

AI agents invoke previous_app to trigger actions in Ulanzi. 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 previous_app needs a policy

This tool triggers an external operation on a physical device (Ulanzi TC001 Smart Pixel Clock) by changing its display state. It doesn't read data, write/create persistent data, delete anything, or involve finances — it executes a control action via the AWTRIX3 HTTP API. The blast radius is low since it only affects which app is displayed on a small pixel clock.

From the tool's definition Switch to the previous app in the display loop

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

previous_app Rate-limited

previous_app 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": {
    "previous_app": {
      "limits": [
        {
          "counter": "previous_app_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 Ulanzi, so you can run agents against it safely.

FAQ

Questions about previous_app

What does the previous_app tool do? +

Switch to the previous app in the display loop. It is categorised as a Execute tool in the Ulanzi MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on previous_app? +

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

What risk level is previous_app? +

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

Can I rate-limit previous_app? +

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

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

previous_app is provided by the Ulanzi MCP server (jelloeater/ulanzi-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.