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

With no annotations, the description carries the full behavioral burden, and it only discloses that the result is an accessibility tree containing refs. It does not explain what refs are for (presumably targets for tap/type), whether the call is read-only, or how much of the UI tree is included (visible vs. full hierarchy).

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?

One short sentence fragment, front-loaded with the resource and its format — no waste. It loses a point only because the terseness is achieved partly by omitting necessary detail rather than by tight editing of complete information.

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?

There is no output schema and no annotations, so the description is the only source of behavioral context, yet it never explains the 'refs' concept that the sibling action tools presumably depend on. For an inspection tool whose output feeds other tools, this leaves a meaningful gap.

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%, with the single 'session' parameter documented as coming from open_app, so the schema does the work. The description adds no additional semantics about the parameter, which is the expected baseline when coverage is high.

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 the resource ('the current screen') and the return format ('accessibility tree with refs'), which is more specific than the bare name 'screen'. However, it is a noun phrase with no verb and never explicitly contrasts itself with the obvious sibling 'screenshot', so the agent must infer that this returns structured UI elements rather than an image.

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?

There is no guidance on when to call this versus 'screenshot' or the other inspection siblings, and no statement of prerequisites beyond what the schema already says. The agent gets no exclusions or recommended sequencing.

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