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

Annotations already declare this a safe, idempotent, read-only, closed-world operation, so the safety profile is covered. The description adds useful context (rates are 2026-specific, returns total plus yearly reduction), though the return detail overlaps the output schema. No mention of eligibility prerequisites or input edge-case behavior.

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?

Four short, front-loaded sentences ordered purpose → usage → inputs → outputs, with no filler. The returns sentence is mildly redundant given the output schema exists, costing it the top mark.

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 present, the return-value contract need not be restated and the description correctly keeps it brief. Combined with fully covered parameters and rich annotations, an agent has everything needed to invoke this correctly.

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%, so both parameters and the duration enum are already documented in the schema. The description merely restates "investment amount, duration (6/9/12y)" without adding meaning such as how the rate scales with duration or why 300,000 EUR is the cap.

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?

Names a specific computation (French Pinel rental investment tax reduction) with a version qualifier (rates 2026), which no sibling duplicates. An agent can distinguish it from the many other French tax/rental calculators (calculate_rental_yield, calculate_property_tax_fr, etc.) without opening the schema.

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?

"Use to evaluate Pinel real estate investment savings" gives a clear positive trigger, and it points to list_bundles for the related 'immobilier' family. It stops short of stating when NOT to use it or naming a sibling alternative for adjacent cases (e.g., general rental yield analysis).

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