key_down

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

Beyond the annotations, it discloses auto-release timing (default 5000, max 30000), overlapping key behavior, and the no-modifier-shortcuts limitation. This adds meaningful behavioral context on top of destructiveHint and openWorldHint. It doesn't describe OS-level side effects, but the annotations already flag destructiveness.

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?

Two short sentences front-load the action and then add constraints. No filler, and every sentence contributes useful information for invoking the tool correctly.

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 two-parameter tool with no output schema, the description covers the core invocation details: which key to hold, how long, and overlap behavior. It doesn't mention early release via key_up or release_all, but those are sibling tools and not required for correct invocation of key_down.

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?

With 0% schema description coverage, the description must carry parameter meaning. It gives an example key format ('KeyA') and explains holdMs semantics with default/max values. However, it mostly restates schema constraints and doesn't clarify the full key pattern or that holdMs is optional.

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 uses a specific verb ('Hold') and resource ('physical key') with an example key name, making the action unambiguous. It also distinguishes itself from key_up by emphasizing automatic release, though it doesn't explicitly name sibling alternatives.

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?

It provides useful context: other keys can overlap, auto-release happens after holdMs, and modifier shortcuts are not supported. However, it doesn't explicitly say when to prefer this over chord, key_up, or sequence_start, so usage guidance is implied rather than stated.

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