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

Beyond the read-only/open-world annotations, it discloses important behavior: up to 20 results per page, the exact fields returned, total count and page price statistics, and datacenter blocking for US/UK sites. It also explains the paid x402 cost and that failed calls are not charged.

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 front-loaded with source, scope, and return fields, and every sentence carries useful information. It is dense and slightly long for a single paragraph, but appropriate for the tool's complexity.

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?

Given the existing output schema and annotations, the description fills the remaining gaps: geographic availability, pagination, returned fields, pricing, and payment behavior. An agent has enough information to decide whether and how to call it.

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 schema already documents every parameter with examples. The description reinforces the available filters but adds little syntax or constraint detail beyond what the schema provides, matching the baseline for full 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 source and resource: vehicle listings from AutoTrader.ca, with geographic scope explicitly limited to Canada. This distinguishes it from the many other vehicle-listing siblings by naming the exact marketplace and country.

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 clear usage context through the Canada-only scope and the note that US/UK AutoTrader sites block datacenter traffic, plus the supported filters. It does not explicitly name alternative sibling tools or say when not to use it, so it falls short of a full 5.

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