Take Screenshot

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

Annotations already declare readOnlyHint=true and openWorldHint=true. The description adds valuable behavioral details: the snapshot is short-lived and frame-validated, and it instructs not to cache beyond the snapshot lifetime. This goes beyond the safety profile provided by annotations and gives crucial operational context.

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 three sentences with no redundancy. The purpose is front-loaded, followed by usage guidance and a caching warning. Each sentence contributes essential 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?

The description compensates for the lack of an output schema by mentioning the returned snapshotId and its usage. It covers the tools purpose, output lifetime, and downstream interaction. Minor omissions (e.g., failure modes, precise meaning of 'frame-validated') are not critical for an agent to invoke it 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?

The schema already covers all three parameters (device, scale, maxSize) with full descriptions at 100% coverage. The tool description does not add any parameter-specific meaning beyond the schema, so the baseline score of 3 applies.

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 states a specific verb ('Take a screenshot') and resource ('mobile device'), and clarifies the output as a 'short-lived, frame-validated snapshot'. It distinguishes itself from similar tools like mobile_save_screenshot by emphasizing the temporary nature, so an agent can tell them apart without opening schemas.

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 provides clear guidance on how to use the returned snapshotId with mobile_click_on_screen_at_coordinates and coordinateSpace=screenshot, and explicitly warns not to cache beyond the snapshot lifetime. It does not, however, explicitly contrast with mobile_save_screenshot for persistent screenshots, leaving a small gap in when-not-to-use guidance.

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