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

With no annotations provided, the description carries the full burden—and it does so well. It discloses that components that cannot be worked out are 'omitted rather than guessed' and that the response will say which are omitted. It also states the condition 'where it can be worked out' for depreciation, giving the agent insight into fallback behavior.

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?

Three sentences with no redundancy: the first states the core function, the second gives input guidance, and the third covers the value proposition and fallback behavior. It is front-loaded with the main purpose and every sentence earns its place.

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 no-output-schema estimation tool, the description covers the key context an agent needs: what is estimated, how to obtain inputs, and how incomplete data is handled. It does not describe the exact output structure (e.g., itemized breakdown vs. total), but the mention that the response says which components are omitted partially compensates for that gap.

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 baseline is 3, but the description adds useful semantic context by explaining that listing_id and listing_url are alternative inputs and that both come from search_used_cars. This resolves any ambiguity about which parameter to pass and reinforces the relationship between the two parameters.

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?

Description states a specific verb ('Estimate') and resource ('what a specific car on Autoza actually costs to own for a year'), then enumerates the cost components: road tax, fuel, servicing, MOT, insurance, and three-year depreciation. It differentiates from siblings by framing the tool as answering the buyer's total-cost question 'rather than just the sticker price', and explicitly references search_used_cars as the source of its input.

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 gives explicit invocation guidance: 'Pass the listing URL or id returned by search_used_cars.' This clarifies both what input to use and where it comes from. It does not explicitly list when to prefer this over related tools like calculate_car_tax, but the aggregate-vs-single-component framing makes the use case clear enough.

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