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

With no annotations, the description carries the full burden and does disclose two real behavioral facts: exact decimal arithmetic (no float rounding surprises) and commission applied on gross price, plus a $0.005-per-call x402 payment requirement. It says nothing about permission/auth flow, sign conventions for negative margins, rounding of results, or default values for the 5 optional inputs.

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?

Two front-loaded sentences: what is computed, then cost factors, then precision guarantee, then price. Zero filler and the pricing disclosure is compact.

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 stateless calculator with no output schema, an agent still needs to know the result shape (single margin figure vs. breakdown) and the percentage/currency conventions. Those gaps matter for a financial tool, though the list of included factors means the agent can call it without guessing wrong inputs in most cases.

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 0% and parameter names are Portuguese, so the description must compensate. It effectively maps the concepts iva_pct (VAT), portes (shipping), comissao_pct (commission), taxa_fixa (fixed fee) and devolucoes_pct (returns). However, it gives no unit convention (is iva_pct 23 or 0.23?), no defaults for the 5 optional fields, and does not directly label preco_venda/custo_produto — the two required parameters.

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 a specific computation (per-sale profit margin) and enumerates the exact cost components it accounts for: VAT, shipping, marketplace commission on gross price, fixed fee and returns. It is domain-scoped to Portugal e-commerce. No sibling differentiation is offered, but the siblings (chat-gpt-oss, detetor-ia-pt, localizar-pt-pt, verificar-anuncio) are unrelated utilities, so confusion is unlikely.

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?

'Per-sale' implicitly scopes it to single-transaction calculation rather than aggregate reporting, which is useful. But there is no explicit statement of when to use it, prerequisites, or what alternative to pick for other computations. Usage is inferable rather than stated.

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