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

With no annotations, the description carries the full burden; it does disclose the upstream source (Central Bank of Brazil), the two bulletin types (Fechamento vs. intraday), and even the price ($0.002), which is useful cost context. It says nothing about authentication, rate limits, or what the payload looks like.

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 front-loads the core capability, with the nominal cost appended. It is compact with little waste, though the enumeration of features is slightly list-like rather than prioritized.

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 two-optional-parameter lookup with no output schema and no nested objects, the description covers the domain (BCB PTAX), currency scope, date range, and bulletin variants. Only the return shape is left implicit, which is minor at this complexity.

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 are already documented in-schema, including the USD and today defaults. The description restates those defaults and adds the currency examples (EUR) but contributes no syntax or format detail beyond the schema, so 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?

The description names a specific verb ('get') and a well-defined resource (PTAX exchange rate from the Central Bank of Brazil), with concrete coverage: USD/BRL, EUR/BRL, buy/sell, closing vs. intraday. It does not explicitly differentiate itself from the sibling get_rates, so it falls short of a 5.

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?

It states defaults (USD/BRL, today) and that a past date is allowed, which implies when to call it, but it never says when to prefer it over get_rates or other rate-related siblings. Usage is inferable rather than guided.

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