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simctl-mcp-server

simctl-mcp-server

by nzrsky
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

simctl_screenshot

Capture screenshots of iOS simulator devices by providing device UDID or name, output path, image format, and display target.

Instructions

Take a screenshot of a simulator device.

Args: device: Device UDID, name, or 'booted' for current device output_path: Path where to save the screenshot format: Image format (png, jpeg) display: Display to capture (internal, external)

Returns: Success message

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "device": "<device>",
      "output_path": "<output_path>"
    },
    "name": "simctl_screenshot"
  }
}

Input Schema

NameRequiredDescriptionDefault
deviceYes
output_pathYes
formatNopng
displayNointernal

Output Schema

NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4/5.0
Behavior3/5

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

With no annotations, the description carries full burden. It states the return is a success message but doesn't disclose whether the screenshot overwrites existing files, what happens if the device is not booted, or any side effects.

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 concise with clear 'Args' and 'Returns' sections. Every sentence serves a purpose, and there is no redundancy.

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

Completeness4/5

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

For a simple screenshot tool, the description covers the essential aspects. It explains parameters and return value. It could mention output file behavior or that the device must be booted, but overall it is adequate.

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

Parameters4/5

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

Schema coverage is 0%, so the description provides the only parameter explanations. It describes each parameter (device, output_path, format, display) and indicates defaults (png, internal), adding value beyond the bare schema.

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

Purpose5/5

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

The description clearly states the tool's purpose: 'Take a screenshot of a simulator device.' It uses a specific verb-resource combination and distinguishes from sibling tools like simctl_boot_device or simctl_record_video.

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

Usage Guidelines3/5

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

No explicit guidance on when to use this tool vs alternatives or prerequisites. The description is straightforward but lacks context like requiring a booted device or mentioning that output_path must be writable.

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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