List Screen Elements

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds value by warning against caching the result, signaling that the output is time-sensitive and may change between calls, and by clarifying that elements are identified via display text or accessibility label.

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?

Two short sentences with no filler. The core purpose is front-loaded, the output contents are specified, and the caching caveat is a meaningful addition that 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?

For a simple read-only tool with one parameter and no output schema, the description covers the main behavior, output contents, coordinate presence, and freshness requirement. It does not detail coordinate units or element ordering, but these are minor given the simplicity and the read-only annotation.

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 the schema already explains the device parameter and even points to mobile_list_available_devices. The tool description itself adds no new parameter semantics, which matches the baseline for a fully documented single parameter.

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 states a specific verb ('List'), a clear resource ('elements on screen'), and the exact output contents (coordinates, display text, accessibility label). This distinguishes it from sibling tools like mobile_get_screen_size, which only returns screen dimensions, and the interaction tools that operate on elements rather than listing them.

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 instruction 'Do not cache this result' gives an important usage constraint, implying the agent should call this fresh each time the current screen state matters. However, it does not explicitly say when to choose this tool over siblings or name alternatives, leaving the usage context mostly implicit.

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