device_do

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

With no annotations present, the description carries the transparency burden. It honestly discloses that exactly one action is run, results are returned, screenshots are off by default due to context cost, and chaining is not performed by the tool. However, it does not disclose side-effect potential for mutating actions, what verification or auto_approval do, or what happens on failure or retry, leaving significant behavioral gaps.

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 reasonably sized and front-loaded with the tool's core purpose, and the screenshot guidance is practical. But it contains redundancy ('one tool for any single... action' vs 'Never plans or chains more than one action') and a confusing 'Jev first picks' narrative that could be stated more directly and compactly.

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 tool with no output schemahol, no annotations, and six parameters, the description is incomplete. It covers core single-action behavior and screenshot usage, but omits the return format, semantics of four parameters, failure/retry behavior, and any relation to sibling tools. An agent would likely need additional information or experimentation to invoke it correctly in all cases.

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 0%, so the description must compensate for all six parameters. It adds meaning for goal (an atomic action from the enumerated list) and include_screenshot (attaches screenshot, off by default, expensive), but verify, direction, auto_approve, and max_attempts remain entirely unexplained in both schema and description.

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 that the tool executes one real phone action at a time and enumerates the supported atomic kinds (open app, tap, long-press, type, swipe, scroll-to-find, press key, toggle service, set DND, take screenshot, read system service). It is more specific than the generic name, but it does not directly distinguish itself from sibling tools device_screenshot and device_approve, especially since 'take a screenshot' is listed among its own action kinds.

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 gives useful context: invoke one atomic action per call, never plan or chain, and request screenshots only at checkpoints because images cost context. However, it does not explicitly say when to prefer device_screenshot or device_approve, nor what conditions would make those siblings the better choice over this tool.

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