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

Annotations already establish read-only, idempotent, non-destructive, and non-open-world behavior. The description adds substantial context beyond that: what counts as addressable, that bounding boxes must intersect the rectangle, the returned fields (attributes, bounds, center coords, ranked locator strategies), and the smallest-first sort order.

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?

Four tight sentences with no wasted words. The core operation and scope are front-loaded, followed by return shape, sort order, and intended use, which is an efficient structure for an agent deciding whether to call it.

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?

The description covers the tool's purpose, matching semantics, return fields, sort behavior, and typical use cases. With no output schema, it still explains what comes back well enough, and annotations cover the safety profile, so 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 description coverage is 100%, so the schema already documents every parameter, making the baseline 3. The description adds meaningful semantics beyond the schema by clarifying that elements are matched by intersection with the rectangle rather than containment and by defining the physical-pixel coordinate space.

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?

States a specific verb (List) and resource (addressable UI elements intersecting a physical-pixel rectangle), including the inclusion criteria (resource-id, text, or content-desc present). It also contrasts with the alternative of parsing the full XML, so an agent can distinguish it from page-source tools without opening another schema.

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?

Gives clear when-to-use guidance with concrete examples (bottom nav, dialog, list section) and an implied alternative ('without parsing the full XML'). It does not name a specific sibling tool or state when-not to use this one, so it stops short of the top score.

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