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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false. The description adds valuable behavioral context by noting that quotes are not published on weekends/holidays, implying the tool may return no data or an error on those days. It also discloses the exact return structure, going beyond what annotations provide.

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?

The description is two sentences, front-loaded with the core purpose, and includes output structure and a key constraint without any fluff. Every word earns its place.

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 simple one-parameter read-only tool with full schema coverage and no output schema required, the description is complete. It explains what is returned, the format, and a critical availability caveat, covering all necessary information for an agent to use it correctly.

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 100%, so the baseline is 3. The description reinforces the date parameter requirement ('specific business day') and the weekend/holiday caveat, but does not add additional syntax or formatting details beyond what the schema already provides. The parameter meaning is fully captured by the schema description.

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 clearly states the tool returns the official PTAX USD/BRL quote for a specific business day, including buy/sell rates and timestamp. It also specifies the exact return fields ({cotacaoCompra, cotacaoVenda, dataHoraCotacao}), making the tool's purpose unambiguous and distinct from any siblings.

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 description implies the tool should be used for specific business days and warns that quotes are not published on weekends/holidays, which gives clear timing context. It does not explicitly name alternative tools, but given the niche nature of PTAX quotes, that is not necessary for effective guidance.

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