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

The annotations already establish read-only, open-world, non-destructive behavior, and the description adds valuable plan-gating context and a cost of 2 credits. It still leaves some behavioral ambiguity around how unsupported paid filters behave on free plans.

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 short and front-loads the purpose, plan capabilities, and credit cost. It does waste some space by repeating 'US Car Models' at the start, but the remaining sentences are efficient.

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?

With an output schema and rich annotations already present, the description adds the key external context an agent needs: coverage years, plan-dependent filters, and credit cost. The main remaining gap is ambiguity around optional parameters and free-plan behavior with restricted filters.

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 schema already documents all four parameters. The description adds meaningful semantics beyond the schema by noting that year and trim filtering are paid-plan capabilities; however, it does not clarify the optional model parameter or the behavior when make is omitted.

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 clearly states that this is a car make/model API for US vehicles from 1984 to present and that it lists models by make. The verb 'List' and resource 'models' are specific, though the description does not explicitly differentiate itself from related siblings such as VINDecoder.

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 gives implied usage by saying models can be listed by make and that paid plans add year, trim, MPG, engine, and transmission filters. It does not explicitly state when to use this tool versus alternatives or what happens if paid-only filters are supplied on a free plan.

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