describe_ui

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

With no annotations, the description carries full burden. It states the output format (label, type, value, enabled, frame) but lacks details on behavior like error handling, performance, or prerequisites (e.g., foreground app needed).

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, front-loaded with 'PRIMARY PERCEPTION' for emphasis. The structure is clean and efficient, though it could be slightly more organized.

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?

Given no output schema and simple parameters, the description adequately explains what is returned. However, it omits context about error conditions or prerequisites. The sibling tools list provides useful context.

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%, so baseline is 3. The description does not mention or elaborate on the parameters (interactive_only, udid); it relies entirely on the schema for their meaning.

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 that the tool returns the accessibility tree as a list of elements, which is a specific verb+resource. It distinguishes itself from sibling tools (tap, swipe, etc.) by focusing on perception rather than actions.

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?

The description includes 'Reason over this and tap by label,' implying that the tool is used to gather information before performing a tap. However, it does not explicitly exclude other uses or provide conditions for when not to use it.

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