get_purchase_costs

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

With no annotations, the description carries full responsibility for behavioral disclosure. It clearly states per-call cost ($0.02), payment mechanism (USDC on Base via x402), compute-first/settle-after billing (never billed for errors), and the need for a private key in live mode. It also hints at output structure (per-line sourceUrl + confidence). This is exemplary transparency for a paid API tool.

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 dense but every sentence contributes value: purpose, jurisdiction breakdown, costing, settlement model, and requirements. It is front-loaded with the core purpose and structured by CA/US sections. No fluff or repetition, making it efficient for an AI agent to parse.

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?

The tool has no output schema, so the description must convey return shape; it does so by noting 'per-line sourceUrl + confidence' and itemizing fee categories. It also covers coverage (all provinces/territories and states), usage constraints, and billing behavior. For a 9-parameter tool, this is a complete picture.

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 100%, so the baseline is 3. The tool description does not add parameter-level semantics beyond what the schema already provides; it only summarizes jurisdiction coverage and fee categories. No additional meaning is imparted for parameters like state, province, or sale_type beyond their schema descriptions.

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 opens with 'Itemized government-imposed used-vehicle closing costs', naming a specific verb+resource with clear scope (Canada and US). It distinguishes itself from siblings like get_pricing or get_recalls by detailing jurisdiction coverage and fee categories, making the tool's purpose unmistakable.

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 provides extensive context on when to use the tool: when used-vehicle closing costs are needed in Canada or the US, with a detailed breakdown of what is included. It also states prerequisites (EVM_PRIVATE_KEY, live mode) but does not explicitly name alternative tools or exclusions, falling just short of a 5.

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