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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds substantial behavioral context beyond annotations: the independence of investorBuy/investorSell, the exact meaning of found:true/false, possible causes for not found (market hours, availability, invalid year), and the decimal-fraction rate convention. It also states that each side may be present independently and how to handle missing investorBuy.

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 long but every sentence adds value. It is well-structured with clear sections for purpose, usage, field semantics, and fallback logic. The most critical constraint (productId + exactly one year) is front-loaded, and the rate format is explained at the end. No fluff or repetition.

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?

The tool has an output schema (not shown) but the description still explains the return structure in detail: investorBuy/investorSell objects with rate and price, fetchedAt timestamp, and the found flag semantics. It also covers error conditions and fallback strategies. Given the complexity of the tool and the available annotations/schema, the description is fully sufficient for an agent to call 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 description coverage is 0%, so the description carries the full burden for parameter documentation. It fully explains the queries array structure, the productId enum values, the maturityYear/conversionYear exclusivity rule, and the required year field for each product type. It also clarifies that omitting the year field errors. This compensates completely for the schema's lack of descriptions.

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 verb ('looks up'), the resource ('live quotes for Tesouro Direto bonds'), and explicitly distinguishes the data source from the STN CSV used by siblings. It also names the fallback tools for non-current data, so an agent can unambiguously tell this tool apart from price_history_* and simulate_bond.

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 gives explicit when-to-use guidance ('Use for current indications only'), tells the agent to consult catalog_list for availability, and prescribes exact fallback behavior when found:false ('fall back to price_history_lookup / price_history_series'). It also details the required parameter combinations (productId plus exactly one year field) and the special case for renda-mais/educa-mais, leaving no ambiguity about invocation conditions.

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