AI agents invoke app_start to trigger actions in uiautomator2 MCP Server. 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.
This tool launches applications on an Android device, which executes external operations beyond the MCP server itself. The effects are dynamic and argument-dependent (which app to start), and reversibility is not guaranteed—a malicious agent could start banking apps to capture credentials, spyware, or other harmful applications.
From the tool's definition Tool name is 'app_start' on a uiautomator2 Android automation server. Sibling tools like 'app_install', 'app_stop', 'app_clear' confirm this server performs device control operations.
Documented attack patterns abuse exactly the kind of access app_start gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and uiautomator2 MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for app_start:
{
"version": "1",
"default": "deny",
"tools": {
"app_start": {
"limits": [
{
"counter": "app_start_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}app_start 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.
Free to start. No card required.
app_start. It is categorised as a Execute tool in the uiautomator2 MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the uiautomator2 MCP Server MCP server in PolicyLayer and add a rule for app_start: 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 uiautomator2 MCP Server. Nothing to install.
app_start is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the app_start 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.
Set action: deny in the PolicyLayer policy for app_start. 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.
app_start is provided by the uiautomator2 MCP Server MCP server (tanbro/uiautomator2-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from uiautomator2 MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
77 uiautomator2 MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.