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

Annotations already declare readOnlyHint=true, destructiveHint=false and idempotentHint=true, so the safety profile is covered. The description adds genuinely new behavioral context: no session prerequisite, a fresh device capture on every call, and the resulting per-shot latency relative to mjpeg. It does not discuss error behavior when the device is unreachable, which keeps it short of a 5.

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?

One sentence, front-loaded with the action and its key differentiator, then the return type, then the sibling tradeoffs. No redundant or filler clauses; every segment carries selection-relevant information.

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 supplies the return format ('Returns PNG image'), the session prerequisite, and the performance tradeoff against alternatives. Combined with full schema coverage on the single parameter, an agent has everything needed to invoke it correctly.

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 schema has a single parameter with 100% description coverage ('iOS device UDID'), so the schema already carries the parameter semantics. The description adds no format or sourcing detail for udid beyond that. Baseline 3 applies when the schema does the work.

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+resource ('Take a screenshot of an iOS device') and immediately scopes it with the distinguishing property '(no automation session required)'. It names and contrasts against both siblings, ios_screenshot and ios_mjpeg_screenshot, so an agent can select it without opening another 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?

Explicitly states the selection condition: use this instead of ios_screenshot when the automation session is not running. It also explains the counter-case against ios_mjpeg_screenshot, noting mjpeg is fast only because a session is already streaming frames. Both when-to-use and when-not-to-use are covered.

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