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

No annotations are provided, so the description carries the full burden. It excels here by disclosing the routing behavior (control channel vs shell), the fallback mechanism, and the special handling for system-policy keys. This is rich behavioral context that an agent needs to understand execution nuances.

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 concise and information-dense, packing key purpose, accepted values, and routing behavior into a compact block. It's front-loaded with the core purpose. Slightly verbose on the routing explanation, but every clause earns its place given the complexity of the behavior.

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 2-parameter tool with no output schema, this description is quite complete. It covers accepted values, routing behavior, and fallback logic. It could mention what happens on failure or what the return value is, but the behavioral coverage is strong. The description is adequate for an agent to select and invoke correctly.

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?

While schema coverage is 100% and both parameters are described in the schema, the description adds value by clarifying the keycode parameter's dual nature (numeric OR named) and listing the specific accepted named keys. It also explains the behavioral difference between system-policy and regular keys, which adds meaning beyond the schema's simple type definitions.

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 tool's function: 'Send a keycode to a device' with specific verb+resource. It distinguishes itself from siblings like device_tap/device_swipe by focusing on keycodes. However, it doesn't explicitly differentiate from ios_key_hid or webpage_press_key, relying on the 'device' prefix for context.

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 explicit guidance on when to use this tool: it explains that system-policy keys always go through shell, while other keys try the control channel first with fallback behavior. It also lists the accepted key names, giving concrete usage direction. This is strong behavioral guidance beyond what the schema provides.

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