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

With no annotations, the description carries the full burden. It discloses the return payload (JPEG + text block with pixel/point sizes and conversion formula), the non-1:1 scaling caveat, auto-wake behavior, and the session requirement. This is comprehensive for a read-only screenshot tool.

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: speed, return content, scaling warning, usage advice, session requirement, and fallback. Front-loaded with the key advantage. No fluff.

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 no output schema, the description fully explains what the agent gets back and why it matters. It covers prerequisites, alternatives, and the critical scaling formula. Nothing essential is 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 covers udid at 100%, so baseline is 3. The description does not add extra meaning to the parameter beyond the session requirement, which is more about usage than the parameter itself. No need for more.

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 ('fast screenshot') and resource ('iOS device via MJPEG stream'), and differentiates itself from siblings by naming ios_screenshot and ios_fast_screenshot. The agent can immediately tell this tool's niche without opening schemas.

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 says when to use (routine per-action checks) and when not to use (no session → use ios_fast_screenshot). Also names the slower alternative (ios_screenshot) and the reason (speed). No ambiguity.

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