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

With no annotations, the description carries the full burden. It discloses that the tool returns PNG, captures fresh from the device on every call (no caching), and is slower than mjpeg. It also states no session is required. It does not describe error conditions or prerequisites like device connectivity, but for a simple screenshot 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?

Two sentences with no filler. The main action and key differentiators are front-loaded, and the comparison to alternatives is concise and informative.

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 tool with one parameter, no output schema, and no annotations, the description provides enough context: what it does, when to use it, what it returns, and its performance trade-offs. It could mention potential errors (e.g., device not connected) but that is minor given the simplicity.

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 parameter (udid) is fully documented in the schema. The description adds no additional parameter details, which is appropriate since the baseline is 3 when the schema already covers everything.

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 clearly states the tool takes a screenshot of an iOS device, and explicitly distinguishes it from siblings ios_screenshot and ios_mjpeg_screenshot by noting the 'no automation session required' and fresh-capture behavior. The verb and resource are specific, and the contrast with alternatives removes ambiguity.

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 explicitly says 'Alternative to ios_screenshot when the iOS automation session is not running' and explains the trade-off versus ios_mjpeg_screenshot (slower per shot but no session needed). This gives clear when-to-use guidance and names specific alternatives.

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