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

Annotations already declare this as a safe, idempotent, non-destructive, closed-world read, so the bar is lower. The description still adds real behavioral value by disclosing the actual depreciation algorithm (Y1 -25%, Y2 -15%, ... Y6+ -5%), which is not derivable from the annotations or schema.

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?

Extremely dense and front-loaded: computation rule first, return shape second, sibling pointer last. Every sentence carries information and nothing is padded.

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 two-parameter calculator with an output schema and full annotation coverage, the description supplies the calculation logic an agent would otherwise lack. The only gap is the absence of guidance on how it relates to other car/finance calculators.

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% (both purchase_price and age_years are documented in the schema), so the baseline is 3. The description's year bands implicitly map to age_years but add no format, unit, or range detail beyond the schema.

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 and resource ('Calculate car residual value') and goes further by spelling out the year-by-year depreciation schedule, so the agent knows exactly what is computed. It does not distinguish itself from the many other car-related siblings (lease_vs_buy, braquet, puissance_fiscale), so it stops short of a 5.

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 only routing hint is 'See list_bundles for related... calculators', which points at a discovery tool rather than explaining when to choose this calculator over alternatives. There is no when/when-not guidance or prerequisite information.

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