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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely useful behavioral context beyond them: input is host-driven and 'Does NOT require an automation session', which materially changes how an agent should sequence its calls.

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 core purpose, then routing guidance, then the key constraint. No filler and nothing repeated from structured fields.

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?

There is no output schema, but the description does summarize the return (HID availability plus display size) and the session requirement, so an agent knows what it gets back. Adding the failure mode (what it reports when HID is unavailable) would make it fully complete.

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% for the single udid parameter, so the schema already documents the only input. The description adds no syntax, format, or constraint detail beyond it, 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?

States a specific verb and resource ('Report whether direct HID input ... is available on an iOS device') and adds the secondary output (display size). It also distinguishes itself from the mass of sibling tools by naming the two families it mediates: the *_hid tools and the session-backed ios_* tools.

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?

'Use to decide between the *_hid tools and the session-backed ios_* tools' gives clear context for when to reach for this tool. It stops short of stating exclusions (e.g. when a session is already open this check is unnecessary), so it is strong but not fully explicit.

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