Choose the vehicle to act on

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

The description discloses an important behavioral trait—'remember it'—indicating that the selection persists and affects subsequent tool calls. Annotations already cover idempotency and non-destructiveness, so the description adds useful statefulness context without contradicting them.

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 with no wasted words. The core behavior is front-loaded, and the usage condition follows naturally, making it easy for an agent to parse quickly.

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 selection tool with one fully documented parameter, an output schema, and clear behavioral guidance, the description is complete. An agent knows what the tool does, when to use it, and how the selection affects other tools.

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?

The schema fully documents the single 'vin' parameter, including the option to use the last four characters from toyota_list_vehicles. The description does not add parameter-level detail, but none is needed given 100% schema coverage.

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 states a specific action: 'Point every other tool at one vehicle of the account, and remember it.' This clearly identifies the tool as a selection/context-switching operation and differentiates it from the many getter/action sibling 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 when to use it: 'Use when the account holds several vehicles, or to switch between them.' It does not mention when not to use it, but the guidance is clear enough for deciding when this tool is relevant.

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