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

Annotations already declare this a safe, non-destructive, closed-world read, so the burden is low. The description adds real behavioral substance beyond that: which taxes are computed, the 0.8% stamp duty figure, the Casa Pronta registry fee, and the three scenario branches (primary residence, second home, under-35 exemption). It omits any caveats about estimation accuracy or output shape, but the output schema covers returns.

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?

Front-loaded and compact: the calculation, jurisdiction and rate year come first, followed by the covered instruments. The Portuguese sentence is near-verbatim duplication of the English and earns only partial credit, but the overall length remains tight and scannable.

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 moderately complex tax calculator with a full output schema, the description is sufficient: it establishes jurisdiction, year, components and eligibility branches. It stops short of noting the mainland-only limitation's consequence for island buyers or that figures are estimates, which leaves a small gap.

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 each of the four parameters is already documented including enum meanings and the €330,539 exemption threshold. The description's mention of 'primary residence, second home, or under-35 exemption' mirrors the finalidade and comprador_ate_35 semantics without adding new syntax or edge-case meaning, so baseline 3 is warranted.

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 (calculates) plus the exact resource (taxes and fees of buying a home), and narrows scope to mainland Portugal with 2026 official rates. It names IMT, stamp duty and land registry explicitly, so it is unmistakable against siblings like pesquisar_imoveis or ver_imovel, which do not compute costs.

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 2026 mainland-Portugal scope is useful context, but there is no explicit 'use this when...' routing and no mention of alternatives or when the tool does not apply (e.g., islands, older years). Usage is only implied by the resource name and the listed transaction scenarios.

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