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

Beyond the readOnlyHint/openWorldHint/idempotentHint annotations, it discloses the API key requirement, that funds are held ('usdt_reserved (held until the PIX completes; the leftover returns)'), that the quote is recomputed at payment time, and that merchant_name must be surfaced to the user before paying. That is exactly the extra context annotations cannot carry.

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 and dense with no filler sentences; the alternation rule and return values come early. The opening 'Requires an API key' is near-boilerplate and the parenthetical about leftover funds is slightly wordy, but nothing is wasted overall.

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 no output schema, the description fully carries the return contract (usdt_total, usdt_reserved, and merchant_name/quote_id for br_code) plus the auth prerequisite, the input alternation, and the minimum-amount constraint. An agent has everything needed to call and interpret this tool 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 adds real meaning on top by clarifying that br_code carries both amount and recipient, and by cross-referencing the minimum valid amount via min_payment_brl from lunium_get_usdt_wallet. The brl_amount explanation largely restates the schema.

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 precise verb and resource ('quote a PIX paid with the USDT balance') and immediately scopes it as side-effect-free ('No effect'), which cleanly separates it from the sibling lunium_pay_pix_with_usdt. An agent can distinguish pricing from payment without opening either schema.

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?

Gives explicit conditional usage for the two input modes ('EITHER brl_amount ... OR br_code') and a prerequisite sourced from lunium_get_usdt_wallet (min_payment_brl). It implies, but never names, lunium_pay_pix_with_usdt as the follow-up action, so it stops just short of full when/when-not routing.

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