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

Beyond the annotations, it discloses the AppState transition, that tap/type/scroll/back will fail with app_not_foreground while backgrounded, that resume_app restores the app, and that the action is logged as simulated. That is exactly the side-effect and failure-mode context an agent needs before invoking it.

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?

Three tight sentences: effect first, resulting failure modes second, recovery path last. No filler, and the most important consequence is front-loaded.

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 one-parameter tool with no output schema, the description covers the state change, the blocked follow-up actions, the recovery tool, and the simulated-logging caveat. Nothing an agent needs in order to call it correctly is missing.

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?

There is a single parameter with 100% schema description coverage ("Session from open_app"), so the schema already carries the meaning. The description adds nothing about the session parameter itself, which is acceptable at this coverage level but earns only the baseline.

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 names a specific verb (press Home) and states the exact resulting state: the app moves to the background with AppState "background" and the phone shows the home screen. This distinguishes it clearly from siblings like resume_app, lock, and open_recents, since it explains the device effect rather than just the name.

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?

It makes the use case and its consequence explicit, and routes the agent to the correct follow-up: call resume_app to bring the app back to AppState "active". It does not contrast with the other backgrounding-flavored siblings such as lock or open_recents, so the when-not guidance is incomplete.

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