key_down

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

With no annotations, the description takes on full burden. It discloses key behaviors: the press stays held until key_up, single-character ASCII strings map to matrix positions, and longer strings route through SPECIAL_KEYS. These are behavioral traits beyond the schema. It does not mention potential effects like key repeat or error handling, but the essential statefulness is well covered.

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 compact and front-loaded with the core action. Every sentence contributes: the first line states the purpose, the second explains key semantics, and the third warns about held state with an alternative. No filler, and the structure aids quick comprehension.

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 only two parameters and an existing output schema, the description covers the essential semantics: what the tool does, how the key parameter behaves, and how it differs from type_input. It does not clarify session_id, but that is minor given the commonality and the presence of an output schema. Overall, the context is sufficiently complete for an agent to select and invoke the tool 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?

Schema description coverage is 0%, so the description must compensate. It thoroughly explains the 'key' parameter: accepts symbolic names or integer codes, with single-character strings treated as matrix positions and longer strings via SPECIAL_KEYS. The session_id parameter is left unexplained, but it is a common context parameter across sibling tools and self-explanatory. The key explanation adds significant meaning beyond the raw schema.

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: 'Inject a raw BBC keydown event into the matrix.' The verb is specific (inject), the resource is a keydown event, and it distinguishes from the sibling type_input by emphasizing 'raw' and the held behavior. The phrase 'raw' also sets it apart from higher-level input 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 description explicitly says to use type_input instead for a tap, providing a clear alternative. It also implies the tool is for held keys and pairs with key_up. However, it does not enumerate all sibling alternatives (e.g., press_caps_lock) or state when not to use it beyond the type_input case, though the provided guidance is strong.

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