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start_app

Launch Android applications on connected devices by specifying package names to initiate testing or usage.

Instructions

Start an app on the connected Android device

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
package_nameYes

Implementation Reference

  • The handler function for the 'start_app' tool. Decorated with @mcp.tool() for automatic registration in FastMCP. Launches the specified Android app package using 'adb shell monkey' command.
    @mcp.tool()
    def start_app(package_name: str) -> str:
        """Start an app on the connected Android device"""
        result = subprocess.run(
            [
                "adb",
                "shell",
                "monkey",
                "-p",
                package_name,
                "-c",
                "android.intent.category.LAUNCHER",
                "1",
            ],
            capture_output=True,
            text=True,
        )
        if result.returncode != 0:
            raise RuntimeError(f"Error starting app '{package_name}': {result.stderr}")
        return f"App '{package_name}' has been started successfully."
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It states the action but lacks details on permissions required, potential side effects (e.g., if the app is already running), error conditions (e.g., invalid package name), or response behavior (e.g., success/failure indicators). This leaves significant gaps for a mutation tool with zero annotation coverage.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, clear sentence with no wasted words, making it highly concise and front-loaded. It directly communicates the core action without unnecessary elaboration, which is efficient for an AI agent to parse quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity of a mutation tool (starting an app) with no annotations, 0% schema description coverage, and no output schema, the description is incomplete. It fails to address key aspects like error handling, return values, or dependencies (e.g., device connectivity), leaving the agent with insufficient information for reliable invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The description doesn't add any meaning beyond the input schema, which has 0% description coverage for the single parameter 'package_name'. Since schema coverage is low, the description should compensate by explaining what a package name is or providing examples, but it doesn't. However, with only one parameter, the baseline is slightly higher, but the lack of additional context keeps it at a minimal viable score.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Start') and target resource ('an app on the connected Android device'), making the purpose immediately understandable. However, it doesn't explicitly differentiate from sibling tools like 'stop_app' or 'install_app', which would require mentioning it launches already-installed applications versus installing new ones or terminating running ones.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance is provided on when to use this tool versus alternatives. For example, it doesn't specify prerequisites (e.g., the app must be installed, the device must be connected) or contrast with tools like 'open_uri' (for launching via URLs) or 'list_apps' (for checking availability). The description assumes context but offers no explicit usage rules.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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