List Screen Elements

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

Annotations already declare readOnlyHint=true, and the description adds behavioral details: it returns coordinates and UI attributes, and warns against caching. This complements the annotations well, though it could mention that the list is of visible elements only.

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 sentences, no filler. The first sentence conveys the core capability, and the second adds usage guidance and a critical warning. Every word 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 list tool with one optional parameter and no output schema, the description fully covers what the tool returns and how to use it. The warning about caching adds important context.

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?

Since schema description coverage is 100% (the only parameter 'device' is fully described in the schema), the baseline is 3. The tool description adds no further 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 UI elements on the current screen with specific attributes like text, accessibility labels, resource ids, and pixel coordinates. This verb+resource combination distinguishes it from sibling tools that perform actions (tap, type, etc.) or query device info.

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 explicitly says 'Use this to find where to tap,' providing clear usage context. It also warns 'Do not cache this result,' which is important for dynamic screens. While it doesn't explicitly exclude scenarios, the guidance is direct and practical.

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