screenshot

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

No annotations are provided, so the description bears the full burden. It does disclose that the tool falls back between two mechanisms, which is a useful internals detail. However, it omits critical behavioral aspects: whether the screenshot is returned as a file, base64, or URL; whether it blocks or is asynchronous; failure modes; and any side effects (e.g., requiring user consent). This is insufficient for a tool with zero annotation coverage.

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 extremely concise—two sentences. It front-loads the primary purpose and then adds a relevant implementation note. No fluff or redundancy. Every word earns its place.

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 a single parameter and no output schema, the description should at least hint at the return format (image? path?), common error scenarios, and any side effects. It also doesn't clarify whether this is a still capture vs. a stream (which the sibling 'screen_stream' covers). Given the simplicity, the gaps are significant and would impair an agent's ability to invoke and interpret results 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 description coverage is 100%, with 'device' described as 'Device ID or name'. The description adds no additional meaning or constraints (e.g., format, lookup behavior). Since the schema fully covers the parameter, a baseline 3 applies; the description doesn't add value beyond that.

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 clear verb ('Capture') and resource ('a screenshot from a device'), specifying the tool's core function. However, it does not explicitly differentiate from the sibling tool 'screen_stream', which could be ambiguous for an agent deciding between capturing a still vs. streaming. The purpose is still unambiguous enough for a 4.

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 use this tool versus alternatives like screen_stream or call. It does not mention prerequisites (e.g., device must be on, permissions needed) or any conditions that would make this tool preferable. The implementation detail about MediaProjection/AccessibilityService is not usage guidance.

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