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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower, and the description still adds real substance: how each system behaves (constant vs falling payment) and the provenance of the default rate (Banco Central average on new housing loans to individuals, latest month). It does not clarify error behavior or whether the output includes a full amortization schedule.

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 with the country scope front-loaded and zero filler. The semicolon-chained clauses about the default rate are packed tightly but each carries information, so little is wasted.

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 must describe returns, and it does list the payment under both systems, total interest, and LTV caps. For a three-parameter, one-required calculator this is nearly sufficient; the main missing piece is routing guidance against the many sibling jurisdiction 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 coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema by explaining what happens when interest_rate is omitted — a Banco Central average rather than a fixed literal. It also frames the loan_amount as reais and the term as years, reinforcing the schema's own notes.

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 the resource precisely (Brazilian mortgage monthly payment) and specifies the two amortization regimes (Price and SAC) plus the companion outputs (total interest, CMN LTV caps). The 'BRAZIL' prefix and the Portuguese-system-specific terms clearly separate it from mortgage_payment_es and mortgage_payment_mx, though no sibling is named and there is no explicit verb ('computes').

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?

Nothing states when to reach for this tool versus taux_courants, purchase_costs_br, or the other national mortgage calculators. Usage is only implied by the tool's nature as a payment calculator, which is the definition of implied guidance rather than explicit when/when-not routing.

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