Observe screen UI

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

No annotations are provided, so the description carries the full burden. It discloses the capture mechanism (uiautomator dump / accessibility-style tree), the return format (numbered element list for tapping), and a key limitation workaround (screenshot fallback for canvas/game/Chrome content). It does not explicitly state read-only safety, performance characteristics, or permission needs, but the observe/capture framing implies a non-mutating operation.

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, front-loaded with the primary action and mechanism, followed by the fallback condition. Every sentence earns its place and there is no redundant repetition of the schema or title.

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?

This is a simple read-only observation tool with one optional parameter and full schema description coverage. No output schema exists, but the description states the return format (numbered element list for tapping) and covers the important fallback behavior. It is complete enough for an agent to invoke correctly.

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 baseline is 3. The description adds meaning beyond the schema's 'Include a PNG screenshot in the response' by specifying when to set includeScreenshot: when the UI tree is not enough, such as games, canvas, or Chrome content. That is useful decision context for the only 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?

States a specific verb+resource: capture the UI hierarchy via uiautomator dump and return a numbered element list for tapping. It distinguishes itself from the screenshot sibling by explaining the includeScreenshot fallback for non-tree content like games, canvas, and Chrome. An agent can tell what this tool does and why it exists relative to phone_screenshot 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?

Gives clear usage context: use this to capture the UI hierarchy and get a numbered element list for tapping, and explicitly set includeScreenshot when the tree is not enough (games, canvas, Chrome content). It lacks an explicit 'when not to use this' statement or named alternatives beyond the parameter fallback, but the guidance is concrete enough for selection.

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