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

With no annotations provided, the description carries the behavioral disclosure burden. It discloses the sorting behavior ('Sorted smallest-first so the most specific element comes back first') and the scope filter (only elements with resource-id, text, or content-desc present). However, it does not state whether this is a read-only operation, whether it may take a screenshot, side effects, or performance characteristics. The key behaviors disclosed are useful but the read-only nature is implicit rather than stated.

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, each earning its place: sentence one defines scope and output, sentence two explains sorting order, sentence three gives concrete usage guidance with examples. No filler, no redundancy with the schema.

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 no annotations, the description does a good job explaining return contents (attributes, bounds, center coords, locator strategies) and sorting behavior. However, it does not disclose the read-only nature explicitly, error conditions (e.g., empty region, invalid coordinates), or the relationship to sibling tools like device_find_element or device_locators_for. For a moderately complex enumeration tool with 6 params and no annotations, it is fairly complete but could mention error/edge cases.

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 all 6 params are documented in the schema. The description adds semantic value beyond the schema: it explains what 'intersects' means for the coordinates, and mentions the limit's role (capping returned elements). It clarifies the physical-pixel unit in the description and coordinates context. The schema provides per-field definitions, so the description modestly supplements rather than restates. Given 100% coverage, baseline 3 applies, but the description adds meaningful contextual meaning around the region semantics and the limit.default.

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 verb ('List'), the specific resource ('addressable UI elements'), the filtering criterion ('bounding box intersects the given physical-pixel rectangle'), and what each element contains ('attributes, bounds, center coords, ranked locator strategies'). It also distinguishes from likely siblings like device_page_source or device_find_element by framing it as region-scoped enumeration without full XML parsing.

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 gives clear context for when to use it: 'Use to enumerate the contents of a region (bottom nav, dialog, list section) without parsing the full XML.' This explains the use case well and contrasts it against full-XML page parsing, but does not explicitly name alternative tools or state when NOT to use it. It does not mention exclusions like non-addressable elements or interaction tools.

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