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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so safety is covered. The description adds genuine behavioral context beyond that: it discloses that estimates may be either the car's own figure or a segment average, and that a rank against comparable cars is returned — a meaningful caveat about data provenance.

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?

A single dense sentence that front-loads the core purpose before listing payload contents. Every clause contributes, though the enumerated list makes it read as a run-on rather than cleanly segmented structure.

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 no output schema, the description carries the return-value burden and does so well, listing components, totals, the segment-average caveat, and the rank. It stops short of clarifying units/currency or what the comparison set for rank is, minor gaps for a cost-modeling tool.

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?

There is a single parameter with 100% schema description coverage, and the schema already documents slug with a format pattern and a concrete example. The description adds nothing about slug, so the baseline of 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 names a specific resource and scope: "One car's true monthly cost of ownership," and enumerates the cost components (loan, insurance, maintenance, fuel). The phrase "one car's" implicitly separates it from compare_true_cost, but no sibling is named explicitly, so differentiation is inferred rather than stated.

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?

There is no when-to-use guidance, no prerequisites, and no mention of the adjacent tools compare_true_cost or cost_index. The singular-car scope weakly implies a single-car lookup, but an agent gets no explicit condition for choosing this tool over its siblings.

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