Take Screenshot

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

The annotation already indicates readOnlyHint=true, which is consistent. The description adds a behavioral note ('Do not cache this result') that goes beyond the annotation. However, it does not detail any potential side effects or specifics about the screenshot capture (e.g., full screen vs. viewport, but given simplicity, a 4 is appropriate.

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 with two sentences, both front-loaded with key information. Every sentence adds value without redundancy.

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 simple tool with one required parameter, no output schema, and clear annotations, the description provides complete guidance on when to use, what it does, and a behavioral note. No further information is necessary.

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 input schema has 100% coverage with a detailed description for the device parameter, so the description does not need to add more. It meets the baseline expectation.

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 clearly states the action ('Take a screenshot') and the resource ('mobile device'), and it distinguishes itself from sibling tools like 'mobile_list_elements_on_screen' by explicitly stating when to use that alternative instead.

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 usage context: use to understand what's on screen, and explicitly states when not to use it (if you need to press an element from the view hierarchy) and what to use instead (list elements on screen).

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