phone_screenshot

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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds the useful 'native-resolution' trait, which matters for coordinate math, but omits device-selection behavior and any snapshot timing caveats.

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?

Two short sentences with no waste; the return format leads and the usage hint follows immediately.

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 read-only tool with no output schema, the description usefully states the return type (PNG) and its downstream use. The only real gap is the unexplained serial parameter and default-device behavior.

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 coverage is 0% and the single 'serial' parameter is completely unexplained. The description says nothing about device targeting or the null default that presumably falls back to a default device, so it does not compensate for the gap.

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?

States a specific verb+resource: returns a native-resolution PNG image, which clearly identifies this as the screenshot tool among siblings. It doesn't name sibling tools explicitly, but the pixel/coordinate framing separates it from element-based tools.

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 phrase 'Use these pixels for coordinate actions' implies the tool's role in a coordinate-based workflow (feeding phone_tap/phone_swipe), but it states no when-not condition and never contrasts with phone_tap_element or phone_find_elements, which are the obvious alternate paths.

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