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boot_simulator

Boot an iOS simulator using its unique device identifier (UDID) to prepare for automated testing and interaction within the app-screen-mcp environment.

Instructions

Boot an iOS simulator by UDID

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
udidYesSimulator UDID to boot

Implementation Reference

  • The 'bootSimulator' method handles the 'boot_simulator' tool request by executing 'xcrun simctl boot'.
    private async bootSimulator(udid: string) {
      try {
        await execAsync(`xcrun simctl boot ${udid}`);
      } catch (error: any) {
        if (!error.stderr?.includes('current state: Booted')) {
          throw new McpError(ErrorCode.InternalError, `Failed to boot simulator: ${error.message}`);
        }
      }
      return {
        content: [{ type: 'text', text: `Simulator ${udid} is booted.` }],
      };
    }
  • src/index.ts:284-295 (registration)
    The 'boot_simulator' tool is registered in the list of available tools.
    {
      name: 'boot_simulator',
      description: 'Boot an iOS simulator by UDID',
      inputSchema: {
        type: 'object',
        properties: {
          udid: { type: 'string', description: 'Simulator UDID to boot' },
        },
        required: ['udid'],
        additionalProperties: false,
      },
    },
  • The 'boot_simulator' tool request is routed to the handler in the switch statement.
    case 'boot_simulator':
      return this.bootSimulator(args.udid as string);
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 ('Boot') but doesn't explain what booting entails (e.g., starting a simulator instance, potential delays, or system requirements), whether it's idempotent, or what happens on failure. This leaves significant gaps for a mutation tool.

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 with zero waste. It's front-loaded with the core purpose and appropriately sized for a simple tool with one parameter.

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 incomplete. It lacks details on behavioral traits, error handling, or expected outcomes, which are crucial for an agent to use this tool effectively in context with sibling tools.

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 schema description coverage is 100%, with the parameter 'udid' fully documented in the schema as 'Simulator UDID to boot'. The description adds no additional meaning beyond this, so it meets the baseline score of 3 where the schema does the heavy lifting.

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 ('Boot') and target resource ('an iOS simulator by UDID'), providing a specific verb+resource combination. However, it doesn't differentiate from sibling tools like 'list_simulators' or 'launch_app' which might be related to simulator management, so it doesn't reach the highest score.

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. It doesn't mention prerequisites (e.g., needing a valid UDID from 'list_simulators'), exclusions, or how it relates to other simulator operations like 'launch_app' or 'terminate_app'.

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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