scroll_screen

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

With no annotations, the description carries the full burden and does disclose two valuable behaviors: units are dp, positive dy scrolls down, and a new screenshot is returned. It omits what happens if nothing scrollable is under the point, whether the scroll is animated/flung and awaited, and whether coverage of the whole list is guaranteed.

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?

A single front-loaded sentence covering target, direction semantics, and return value with no filler. Every clause 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 simple gesture tool with no annotations and no output schema, the description covers the essentials including the return value. It still leaves edge-case behavior (non-scrollable target, simultaneous dx/dy, scroll completion) unspecified, which matters for reliable invocation.

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% for four parameters, so the description must compensate. It explains x/y as the anchor point and gives dy's unit and sign convention, but leaves dx's sign, whether dx and dy can be combined, and what happens if both are omitted or zero entirely undocumented.

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 (scrolls), a specific target (the ScrollView/FlatList under a coordinate), and the direction semantics. This clearly separates it from siblings like click_screen, refresh_screen, and press_key.

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 'under (x, y)' implies the point must land on a scrollable container, which is useful implied guidance. However, there is no explicit when-to-use versus alternatives (e.g., refresh_screen to re-capture, press_key for keyboard-driven navigation) and no statement of what happens when the point is not over a scrollable.

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