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launch_app

Launch iOS apps on simulators by specifying bundle identifiers to test and automate mobile applications in controlled environments.

Instructions

Launch an app on a simulator

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
bundle_idYesApp bundle identifier (e.g. com.example.myapp)
udidNoSimulator UDID (optional, defaults to booted simulator)

Implementation Reference

  • The handler function that executes the `launch_app` tool logic using `xcrun simctl`.
    private async launchApp(bundleId: string, udid?: string) {
      const target = await resolveUdid(udid);
      try {
        const { stdout } = await execAsync(`xcrun simctl launch ${target} ${bundleId}`);
        return {
          content: [{ type: 'text', text: `Launched ${bundleId} on ${target}. ${stdout.trim()}` }],
        };
      } catch (error: any) {
        throw new McpError(ErrorCode.InternalError, `Failed to launch app: ${error.message}`);
      }
    }
  • The schema definition for the `launch_app` tool.
    name: 'launch_app',
    description: 'Launch an app on a simulator',
    inputSchema: {
      type: 'object',
      properties: {
        bundle_id: { type: 'string', description: 'App bundle identifier (e.g. com.example.myapp)' },
        udid: { type: 'string', description: 'Simulator UDID (optional, defaults to booted simulator)' },
      },
      required: ['bundle_id'],
      additionalProperties: false,
    },
  • src/index.ts:498-499 (registration)
    The tool registration handler that maps the `launch_app` tool call to the `launchApp` function.
    case 'launch_app':
      return this.launchApp(args.bundle_id as string, args.udid);
Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the action ('Launch') but lacks details on permissions, side effects (e.g., if it affects other apps), error handling, or what happens if the app is already running. This is inadequate 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, efficient sentence that directly states the tool's purpose without unnecessary words. It's front-loaded and wastes no space, making it highly concise and well-structured.

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 tool's complexity (a mutation operation with no annotations and no output schema), the description is insufficient. It doesn't explain behavioral traits, return values, or error conditions, leaving gaps that could hinder an AI agent's ability to use it correctly in context with siblings.

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?

Schema description coverage is 100%, so the schema fully documents both parameters (bundle_id and udid). The description adds no additional meaning beyond implying the tool uses these parameters, which meets the baseline for high schema coverage without compensating value.

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 ('Launch') and the target ('an app on a simulator'), which is specific and unambiguous. However, it doesn't distinguish this tool from sibling tools like 'boot_simulator' or 'terminate_app' in terms of scope or relationship, missing explicit differentiation.

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?

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing a booted simulator), exclusions, or how it relates to siblings like 'boot_simulator' (for starting the simulator) or 'terminate_app' (for stopping apps), leaving usage context unclear.

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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