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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description earns credit for adding context the annotations do not: that billing terms differ per payment method (Pix/USDC = 30 days non-renewing, card = monthly auto-renew) and that `account` comes back as `null` when no credential is supplied. That conditional-output behavior is exactly the kind of thing an agent cannot infer from structured fields.

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?

Three short sentences, front-loaded with what is returned before the billing nuance. The billing sentence is slightly dense ('Pix and USDC pay 30 days') but every sentence carries information an agent would otherwise lack.

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 carries the burden of explaining returns. It names the top-level shape (plans + `account`) and the null case, but never says what a plan record contains (price, interval, id) or whether the list is ordered or paginated, which leaves an agent under-informed about the payload it will have to reason over.

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?

The tool takes zero parameters, so the baseline is 4. The description still adds the useful semantic point that the response shape depends on whether an account or wallet credential is present, which goes beyond an empty 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?

The description clearly states what the tool returns: the catalogue of plans for sale plus the caller's active plan. It is a readable listing tool, though it never distinguishes itself from similarly named siblings such as 'pricing' or 'consulta_planos', so an agent still has to guess which of them to call.

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?

Usage is only implied: reading available plans is the natural precursor to 'buy_plan' or 'cancel_plan', and the payment-terms sentence hints at comparing options. There is no explicit statement of when to choose this over 'pricing' or 'consulta_planos', and no stated prerequisites.

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