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List physical devices and simulators

listTraceDevices

List iOS devices and simulators with UDIDs, including offline ones, to identify the correct device for performance tracing.

Instructions

[mg.discover] Run xcrun xctrace list devices and return parsed devices/simulators with their UDIDs. The LLM should call this before recordTimeProfile to discover the right UDID without asking the user. Set includeOffline: true to include disconnected devices.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "listTraceDevices"
  }
}

Input Schema

Name	Required	Description	Default
`includeOffline`	No	Include devices listed under "Devices Offline" (default false).

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.7.0May 3, 2026

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 the full burden. It explains it runs a shell command and parses output, and describes the parameter behavior. However, it does not disclose potential side effects, required permissions, or return format details, which are typical for a list 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 two sentences with an additional sentence for the parameter, all front-loaded with the main action. No unnecessary words or 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?

Given the tool's simplicity (1 param, no output schema, no nested objects), the description covers the essential aspects: what it does, when to use it, and a parameter detail. It could mention the output format but is adequate overall.

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 coverage is 100% with one parameter described. The description adds the term 'disconnected devices' as a synonym for 'Devices Offline', but this is marginal improvement over the schema's existing description. Baseline 3 applies.

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 runs 'xcrun xctrace list devices' and returns parsed devices/simulators with UDIDs, which is a specific verb+resource. It distinguishes itself from siblings by being the pre-requisite for recordTimeProfile and for device discovery.

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

Usage Guidelines4/5

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

The description explicitly tells the LLM to call this before recordTimeProfile to discover the right UDID without asking the user, providing clear when-to-use context. It also explains the includeOffline parameter but does not explicitly mention when not to use the tool.

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