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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description adds substantial unstated context: no API key required ('ABERTO, sem chave'), morning indicative rates, buy/sell are source labels from the investor's perspective, nominal vs real rates are not directly comparable, numbers are not recalculated, and the response carries source, license (ODbL 1.0) and citation.

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 with what the tool returns and the zero-argument default, then parameters, then interpretation caveats. Dense and mostly waste-free, but the single run-on block mixes defaults, filters and financial semantics without visual separation, making it harder to scan.

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 five all-optional undocumented parameters and no output schema, the description supplies everything needed: defaults, each filter's effect, rate-type interpretation, and the fact that the response contains source, license and citation. Nothing required to call it correctly is missing.

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%, so the description carries the full burden and does most of it: it enumerates the eight accepted titulo values, gives the AAAA-MM-DD format for data and vencimento, explains that data means 'last base date up to that date', that titulo+vencimento returns a daily series, and that de/ate slice that series. It leaves the format of de/ate implicit and does not say what happens if de/ate are supplied without titulo+vencimento.

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 resource (daily rates/prices of Tesouro Direto bonds) with scope (public yield curve by maturity, since 31/12/2004) and provenance. It is unmistakable against siblings such as bdr, etf, fiis_ranking or precos, which cover entirely different asset classes.

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?

Explicitly defines the default invocation ('sem argumentos: todos os títulos no dia-base mais recente') and three distinct usage modes keyed on titulo, data, and titulo+vencimento. It does not name sibling alternatives or say when a different tool would be preferable, which keeps it short of a 5.

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