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

Annotations already establish it as read-only and non-destructive. The description adds useful behavioral context: data source (fueleconomy.gov), response format (JSON), and the monetization/payment requirement ($0.003 USDC via x402). This goes beyond what annotations provide, though it does not detail response shape or possible multiple variants.

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 concise sentences with no wasted words. The core purpose leads, followed by essential operational details: data source, output format, and price. Every sentence adds value.

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 simple three-parameter lookup tool, the description covers the inputs, the return data, the source, the format, and the payment requirement. It does not describe edge cases such as multiple engine/trim variants for the same year/make/model, but the description is reasonably complete overall.

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%, but the individual parameter descriptions are minimal and tautological ('manufacturer', 'model year', 'model name'). The tool description also repeats year/make/model without adding format constraints, normalization rules, or examples. Per the baseline for high schema coverage, a 3 is appropriate.

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 action and resource: 'Fuel economy lookup (EPA)' using year/make/model, and clearly identifies the output as EPA MPG figures and estimated annual fuel cost. This makes it easy to distinguish from vehicle-related siblings like vehicle_report, vehicle_vin, and vehicle_deal_check.

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 clear context for when to use the tool: whenever EPA MPG figures or estimated annual fuel cost for a specific year/make/model are needed. It does not explicitly name alternatives or exclusions, but the highly specific lookup purpose makes usage unambiguous.

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