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

Annotations already cover the safe read-only, idempotent, non-destructive profile, and the description adds real context on top: the absence case is explicitly not an error and returns {"present": false}, and it discloses the prerequisite of an active iOS automation session. That is exactly the kind of behavioral detail structured fields cannot carry.

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?

Four short sentences, front-loaded with purpose, then rationale, then the absence semantics, then the session prerequisite. Each sentence supplies a distinct fact and none is 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?

With no output schema, the description carries the burden of describing returns and does so partially: it names text and button labels as readable and gives the exact empty result. The shape of the present=true payload is not spelled out, but the agent has enough to call and interpret the tool.

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?

Only one parameter (udid) exists and schema description coverage is 100%, so the schema fully documents it. The description adds no syntax, format, or device-selection detail beyond the schema, making the baseline 3 correct.

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 states a precise verb+resource: checking whether a system or app alert is blocking the iOS UI and reading its text and button labels. This is clearly separable from the sibling ios_alert_respond, which acts on alerts rather than reporting their state, so an agent can route correctly without opening either schema.

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?

It gives concrete when-to-use guidance: check before trusting a tap that 'succeeded', because an alert swallows taps aimed behind it. It does not name an alternative tool or state when this check is unnecessary, so it stops short of the explicit when/when-not/alternatives pattern.

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