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

With no annotations, the description carries the load and does well: it discloses the unsigned/prepare nature (nothing is executed directly), the required approve-for-exact-price step, and the dependency on the public sale being open. It stops short of covering failure modes (insufficient balance/allowance, vehicle already owned) or what the returned payload is, which for a prepare tool would be genuinely useful.

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?

Front-loaded with the action, currency, and the sibling redirect; every clause is informative. The middle section on Night Run racing and Hauler cargo/armour is tangentially helpful for model choice but stretches the sentence chain and could be trimmed or split.

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?

No annotations and no output schema, so the description has to cover the workflow itself — and it does: currency split, model taxonomy, prerequisite state, and the approve/buy sequence. The remaining gap is the return shape (presumably unsigned transaction data) and error conditions, which a prepare tool should at least hint at.

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 100%, so the baseline is 3, but the description goes beyond it by mapping each model id to a name (1 Sentinel, 2 Hauler, 3 Courier) and explaining what those choices mean mechanically — racing eligibility vs. cargo and armour. That is decision-relevant semantics the schema's bare '1 to 3 for ZENI' does not supply.

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 and resource ('prepare (unsigned) the purchase of a GROUND vehicle') plus the currency (ZENI) and the model range, immediately distinguishing it from the ETH sibling prepare_vehicle_buy_eth which is named explicitly. An agent can pick the correct tool without opening either 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?

Gives explicit routing conditions: use this for models 1-3 paid in ZENI, use prepare_vehicle_buy_eth for 4-5 paid in ETH, and consult vehicle_shop to confirm the public sale is open. Prerequisites and the approve-then-buy two-step are spelled out rather than inferred.

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