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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds the session prerequisite, which is genuinely useful, but does not disclose the return shape (width alone vs width+height), which is the main behavioral unknown.

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 short sentences, front-loaded with the purpose, then usage, then prerequisite. Every sentence carries distinct information 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 read-only tool with full annotation coverage and no output schema, the description covers purpose, usage and prerequisite adequately. The only remaining gap is clarifying whether the result is width only or full window dimensions, which the name/description mismatch leaves open.

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 coverage is 100% and the single 'udid' parameter is documented in the schema, so the description need not repeat it. The description adds no extra syntax or format detail beyond the schema, making the baseline 3 appropriate.

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 specific verb and resource ('Get the screen width of an iOS device') and scopes it to the automation session, so an agent can identify it among the many ios_* siblings. However, it says 'screen width' while the name/title say 'window size', leaving some ambiguity about whether only width or both dimensions are returned.

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 a clear intended use ('Use these dimensions for tap/swipe coordinates') and a prerequisite ('Requires an active iOS automation session'). No alternative tool is named, but the context for using it is unambiguous.

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