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

The description discloses a lot of behavior that the annotations do not: unpaid calls return a 402 with a price in dollars and reais, the body uses x402 v1 while PAYMENT-REQUIRED uses v2, the balance is held by the account holder or by the wallet that confirmed payment, unpaid wallets need the signed challenge to get an mmw_… credential, and a payment grants no login. It also states that a plan adds 30 days plus quota while a package is valid 90 days, and that there is no automatic renewal. This is exactly the extra context the 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?

The purpose is front-loaded in the first sentence, but the rest is a dense run-on of cryptic clauses such as 'The body uses x402 v1; PAYMENT-REQUIRED uses v2' that require prior knowledge to parse. Most of the information earns its place, but it needs restructuring.

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, so the description has to carry the return path, and it does: the 402 quote, the credential URLs (wallet_start and wallet_token), and the balance-holder semantics. It doesn't cover error cases besides 402, but it is complete enough for this money-moving tool.

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 100%, and the schema already documents the idempotency mark, the offer list, the x402 payment and the cred_… token. The description only adds the framing that the offer is one package plus three plans and that credit versus x402 are the two payment paths. Baseline 3 applies.

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 names a specific verb and resource: it buys one package or one of three plans, paid by credit or x402, with or without an account. That is far more specific than the title 'Buy lookups'. It never names the sibling it complements (consulta_planos for choosing a plan, api_access_buy for API plans), so differentiation is implied by subject matter rather than stated.

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 explains the purchasing procedure in detail (unpaid call returns a 402 quote, then sign the x402 payment), which is real invocation guidance. But it never says when to pick this over consulta_planos, pricing, billing, or api_access_buy. An agent can infer the flow but has to guess at routing.

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