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

No annotations are provided, so the description carries the disclosure burden. It does surface a genuinely useful behavioral trait — the x402 paid-call model ($0.001/call in USDC on eip155:8453) — but says nothing about rate limits, error behavior, or response format.

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 purpose and inputs are front-loaded in one dense sentence, with pricing appended. Slightly awkward em-dash stacking, but no wasted sentences and the key information comes first.

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 4-required-parameter calculator with no output schema and no annotations, the description covers inputs, the computed outputs, and the cost model. It could note result rounding or currency for cost, but the essentials an agent needs are present.

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 real meaning by pinning units (L/100 km, price per liter) and clarifying the vague 'people' parameter as cost splitting between passengers, which the schema only calls 'Split between'.

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?

States a specific verb (calculate) and two concrete outputs (liters of fuel, total cost) with the exact inputs that drive them (distance, consumption, price per liter). Among a sibling set of unrelated unit calculators, the fuel/trip domain is unmistakable, though it never explicitly contrasts itself with any sibling.

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?

Usage is implied by the stated purpose — you invoke it to compute trip fuel cost. The mention of 'optional cost splitting between passengers' hints at a secondary scenario, but there is no explicit when-to-use, when-not-to-use, or alternative named.

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