List Screen Elements

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

Annotations declare readOnlyHint and openWorldHint, so the safety profile is already covered. The description adds genuinely new behavior: refs and coordinates are screen-state-scoped and become stale after navigation or layout change, which is critical for correctly chaining calls. It doesn't mention output volume or pagination, keeping it short of a 5.

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 tight sentences with zero filler: purpose and return shape first, then consumer routing, then the staleness rule. Front-loaded and every sentence earns its place.

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?

There is no output schema, but the description itself enumerates what is returned (ref, coordinates, display text/accessibility label) and how to consume it. For a two-parameter read tool with full schema coverage and annotations, nothing an agent needs to call it correctly 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% and both parameters (device, format with its text/json enum) are fully documented in the schema. The description adds no parameter-level detail, so the baseline 3 applies.

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 and resource ('List elements on screen') and immediately names the returned fields: ref, coordinates, display text/accessibility label. That lets an agent distinguish this discovery tool from the sibling action tools without opening the 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?

Explicitly routes the output to three named consumers (mobile_click_on_screen_at_coordinates, mobile_double_tap_on_screen, mobile_long_press_on_screen_at_coordinates) and gives a lifecycle rule: refs stay valid until the screen changes, so re-list only after navigation or layout change. There is no explicit when-not clause, but the conditions that select this tool are clear.

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