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

With no annotations, the description carries the full burden. It usefully discloses the response shape ('each value with unit and reference date') and the cost ('$0.005'), which are non-obvious traits. It says nothing about authentication needs, rate limits, update cadence, or whether historical values are retrievable.

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?

Three tight sentences: content first, response detail second, price last. Every clause carries information and nothing is padded.

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?

There is no output schema and no annotations, so the description must (and does) describe the returned fields, their units, and their reference dates. It is nearly complete for a simple read-only data feed; only freshness/update behavior is left unstated.

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?

The tool takes zero parameters, so the schema has nothing to explain and the baseline is 4. There are no parameter nuances the description could add.

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+resource ('Current Brazilian indicators from the Central Bank (SGS)') and enumerates exactly which series are returned: Selic target, CDI annual/daily, IPCA monthly/12-month, USD/BRL sell. No sibling tool overlaps with this, so an agent can select it unambiguously.

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?

Usage is implied by the content list (call this when you need Brazilian macro/rate figures) but there is no explicit when-to-use, when-not, or alternative-tool guidance. For a zero-parameter snapshot tool the implication is strong, but nothing is stated outright.

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