Take Screenshot

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

Annotations already declare readOnlyHint=true and openWorldHint=true, covering the safe-read and dynamic-world aspects. The description adds value beyond annotations by warning 'Do not cache this result,' which complements the openWorldHint and is non-obvious. It also clarifies that a screenshot is a visual observation, not an interaction mechanism, which is a meaningful behavioral trait beyond what annotations express.

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 filler. The primary purpose is front-loaded, followed by a relevant usage exclusion and a concise caching directive. Every sentence 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 one well-documented parameter, clear annotations (readOnlyHint, openWorldHint), and no output schema, the description covers the essential context: what it does, when to use it, when not to, and a handling caveat. The only minor gap is that it doesn't explicitly describe the return format, but this is a minor omission for such a simple, self-evident tool.

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%, so the schema already fully documents the single 'device' parameter, including pointing to mobile_list_available_devices. The description itself adds no parameter-specific meaning beyond what the schema provides. Baseline 3 is appropriate since the schema carries the semantic weight.

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 action ('Take a screenshot') and resource ('the mobile device'), and clarifies its purpose: 'Use this to understand what's on screen.' It also distinguishes itself from the sibling mobile_list_elements_on_screen by noting that if the agent needs to press an element available through the view hierarchy, it must list elements instead. This makes the tool's role unambiguous relative to its siblings.

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 explicit when-to-use guidance ('Use this to understand what's on screen') and explicit when-not-to-use guidance with a named alternative ('if you need to press an element that is available through view hierarchy then you must list elements on screen instead'). It also adds a direct operational instruction: 'Do not cache this result.' This fully orients an agent on when to invoke this tool versus alternatives.

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