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

No annotations are provided, so the description carries full burden. It discloses the auto-wake behavior on black frames, the session requirement, and clarifies the image is NOT 1:1 with device points. It doesn't detail failure modes or what happens without an active session, but the key behavioral traits are surfaced clearly.

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?

Every sentence earns its place: purpose, output format, key conversion formula warning, usage recommendation, auto-wake behavior, and session requirement. Front-loaded with 'PREFERRED fast screenshot' for immediate recognition. No filler or redundancy.

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 single-parameter tool with no output schema, the description is remarkably complete. It explains the return value (JPEG + text block with conversion formula), the critical pixel/point distinction, when to use it, and the prerequisite. The complexity is low, and nothing important appears missing.

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, which is self-explanatory ('iOS device UDID'). The description doesn't add parameter-specific detail beyond what the schema provides, but with only one simple parameter and full coverage, the baseline of 3 is 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 clearly states the tool captures a fast iOS screenshot via MJPEG stream, returns a JPEG plus pixel-to-point conversion info. It distinguishes itself from ios_screenshot by naming it as the faster alternative ('Much faster than ios_screenshot') and specifically calls out the scale-conversion formula as its key value-add.

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?

Explicit guidance on when to use this tool ('use it for routine per-action checks') and implies when not to (ios_screenshot is the slower alternative). Names the alternative explicitly (ios_screenshot), states the requirement (active iOS automation session), and flags the #1 pitfall (pixel-to-point scale guessing).

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