Press a key

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

With no annotations, the description carries the full burden. It contributes real behavioral information by defining the accepted key vocabulary, including the escape hatch of arbitrary Android KEYCODE_* names, but says nothing about required device state (connected/unlocked), what happens on an invalid key, or whether anything is returned.

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 sentence, front-loaded with the verb and resource, then the value domain. Every token earns its place and there is no restatement of the title or name.

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 two-parameter input-injection tool with no annotations and no output schema, the description covers the essential unknown — the valid key set. It stops short of device-state and error behavior, but nothing structurally required is missing.

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 only 50% and the undocumented parameter is the required one ('key'), so the description's enumeration of valid values — which the schema lacks entirely, since there are zero enums — is exactly the compensation needed. 'serial' is already documented in the schema and the description correctly leaves it alone.

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 ('Press') plus the resource class ('hardware or navigation key') and then enumerates the exact accepted values, so an agent can immediately distinguish it from phone_type (text entry) or phone_tap (coordinate touch) without opening any schema.

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 list of key names implicitly tells the agent when this tool applies, but there is no explicit when/when-not guidance and no mention of the alternatives (phone_type, phone_tap, phone_shell) or prerequisites such as an active device connection. Usage is inferable rather than stated.

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