device_pinch

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

With no annotations, the description carries the full burden of behavioral disclosure. It reveals the Android-specific UIAutomation injection method and that no root is needed, but it states 'Works on real Android phones' while the schema allows 'ios' as a platform enum value, creating a misleading inconsistency. It also doesn't mention whether it works on emulators or limitations when coordinates are invalid.

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 definition is two sentences with no filler. The primary purpose is front-loaded, and the unusual direction semantics are clarified immediately in the second sentence. 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 7 parameters and no output schema, the description covers core behavior and platform specifics but leaves gaps. The platform inconsistency is an important missing clarification, and it does not mention failure behavior, coordinate system edge cases, or how the tool reports results (even though no output schema exists).

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 71%, so most parameters are already described. The description repeats the direction mapping that is already in the schema (e.g., 'out' = zoom in) but adds no new information about parameters such as spread, duration, or coordinate units. It does not compensate for the ~29% of parameters lacking schema descriptions (deviceId, platform).

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 a specific action: performs a pinch gesture (two-finger zoom), and uniquely clarifies the non-intuitive direction mapping ('out' = zoom in, 'in' = zoom out). This effectively distinguishes it from sibling tools like device_swipe, device_tap, and device_rotate_gesture.

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 implies when to use the tool (for pinch/zoom gestures) through its explicit purpose, but does not explicitly name alternatives or provide exclusion criteria. It is clear enough given the tool name and sibling context, but lacks explicit routing guidance such as 'use this instead of device_swipe when you need a two-finger gesture'.

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