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

With no annotations, the description carries the behavioral burden. It discloses the return payload (bundleId, name, pid) and the session requirement, and the verb 'Get' reasonably implies a read-only operation. It stops short of describing error behavior when no session exists, but for a simple query tool this is adequate.

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?

The description is two tight sentences: the first states the tool's purpose, and the second states the output and precondition. Every sentence earns its place with no filler.

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?

For a one-parameter query tool without an output schema, the description covers the target, the return fields, and the key prerequisite. It lacks only minor context such as failure behavior and how to establish the active session, but nothing essential is missing.

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?

The single parameter udid is already fully described in the schema as 'iOS device UDID', so schema coverage is 100%. The description adds no further parameter context, which is acceptable but not value-adding beyond what the schema provides.

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?

The description uses a specific verb ('Get') and resource ('currently active (foreground) app on an iOS device'), and further specifies the return fields. This clearly distinguishes it from the many sibling tools that deal with app lists, launch times, or performance.

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?

The description gives a clear precondition—an active iOS automation session—but does not name alternatives or explain when to prefer this tool over similar ones like device_current_app or ios_list_apps. The use case is implied by the purpose rather than explicitly contrasted with siblings.

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