List Screen Elements

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

Annotations already declare readOnlyHint=true. The description adds that the tool outputs coordinates and either display text or accessibility label, and explicitly instructs not to cache the result. This provides useful behavioral context beyond the annotation.

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?

The description is two concise sentences, front-loading the core action and adding one critical instruction. Every sentence earns its place without repetition or fluff.

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 the simple tool with one parameter, good annotations, and no output schema, the description is complete enough. It explains the output (coordinates, text/label) and adds a caching directive. It does not detail the output format, but that is acceptable without an output schema.

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?

The input schema has 100% coverage, so the description's parameter semantics are not critical. The schema itself describes the device parameter well, including a reference to another tool. The description does not add additional parameter meaning beyond what the schema provides.

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 tool lists screen elements with their coordinates, display text, or accessibility label. This is a specific verb+resource combination that distinguishes it from sibling tools like mobile_list_apps or mobile_list_available_devices.

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 does not explicitly state when to use this tool versus alternatives, but the context is clear: it's for retrieving UI element information. The parameter description cross-references mobile_list_available_devices, providing a prerequisite hint. The 'Do not cache' instruction adds a behavioral guideline.

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