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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safe, pure-calculation profile is covered. The description adds the fact that the result is an 'estimate' with an 'eligibility note', but 'Returns estimated benefit and eligibility note' largely duplicates the output schema, so the added behavioral value beyond structured fields is modest.

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 sentences, front-loaded with the definition and purpose before inputs and cross-references. Slightly wasteful in restating inputs/returns that the schema and output schema already carry, but nothing is padded or ambiguous.

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?

Both parameters are fully specified in the schema, an output schema exists (so return format needn't be explained), and annotations cover the safety profile, leaving little for the description to fill. It still supplies the CAF/France framing and a related-calculator pointer, making it complete enough for an agent to call 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%: 'salary' is documented as net monthly salary in euros and 'household_size' as number of people (1-6). The description's 'net monthly salary, household composition' is a loose gloss that adds no syntax, unit, or constraint detail beyond the schema, so the baseline 3 applies.

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 verb ('Estimate') and a precise resource ('French prime d'activité monthly amount (CAF benefit)'), which is unmistakable among the many France-finance siblings such as calculate_housing_aid or calculate_french_income_tax. It also states the target user (low-income workers checking eligibility), so the tool's identity is clear 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 for low-income workers checking eligibility' gives clear situational context for when this calculator applies rather than a generic one. It offers no explicit when-not conditions and does not name a competing sibling, only pointing to list_bundles for related calculators, so it stops short of the 5-level routing guidance.

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