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

With no annotations, the description fully discloses key behaviors: it only returns elements whose bounding box intersects the rectangle, it returns attributes, bounds, center coords, and ranked locator strategies, and it sorts smallest-first so the most specific element appears first. This goes well beyond the schema and provides realistic expectations for output ordering and content.

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?

Three sentences deliver all essential information without padding: the operation, output contents, ordering behavior, and a concrete use case. Every sentence earns its place, and the most actionable information appears first.

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?

Despite lacking an output schema and annotations, the description explains what is returned, how results are sorted, what qualifies as addressable, and when to use the tool. The optional limit parameter's default is documented in the schema, so nothing critical is missing for an agent to invoke this 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?

Schema description coverage is 100%, so baseline is 3. The description reinforces that the rectangle is in physical pixels and that elements are selected by bounding-box intersection, but it does not add new per-parameter detail beyond the schema's clear field descriptions.

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?

Description uses a specific verb 'List' and a clearly defined resource: addressable UI elements in a given physical-pixel rectangle. It defines 'addressable' precisely (has resource-id, text, or content-desc) and states the intersection criterion, so an agent knows exactly what the tool returns and can distinguish it from page-source or find-element tools.

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 final sentence gives an explicit use case: 'Use to enumerate the contents of a region (bottom nav, dialog, list section) without parsing the full XML.' This tells an agent when to invoke it, though it does not explicitly name alternatives like device_page_source or ios_elements_in_region.

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