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

Adds substantial behavior beyond the annotations: the call returns immediately (async playback), the simulated location persists until ios_clear_location is called, and the tool requires iOS 17+. These are exactly the non-obvious traits an agent needs, and none contradict destructiveHint=false.

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

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

Three dense sentences with zero filler: behavior first, then the two input modes and pace, then the lifecycle and platform requirement. Every clause carries information the agent needs.

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

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

With no output schema, the description compensates by explaining that it returns as soon as playback starts and how to observe progress via ios_get_location. For a non-idempotent, non-destructive mutation tool, nothing material is left unexplained.

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

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

Schema description coverage is 100%, so the schema already documents udid, gpxPath, waypoints and secondsPerLeg including mutual exclusivity. The description restates pace and ordering but adds no syntax or format detail the schema lacks, so the baseline 3 applies.

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

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

States a specific verb and resource ('Replay a moving GPS route on an iOS device') and immediately distinguishes the behavior from a static set ('an app under test sees travel rather than a teleport'), which is exactly the axis on which it differs from sibling ios_set_location.

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

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

Explains the two mutually exclusive input modes (waypoints vs gpxPath) and the lifecycle: poll ios_get_location to watch progress, call ios_clear_location to stop. It never explicitly names ios_set_location as the alternative for a static position, so routing is inferred rather than stated.

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