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

With no annotations, the description carries the transparency burden. It discloses the authentication requirement and indicates a read-only retrieval ('Retorna informações'), but it does not mention potential rate limits, whether the call consumes quota, or the output format.

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 short sentences with no filler. It frontloads the core purpose and then adds the auth prerequisite.

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 no output schema, so the description should clarify what information is returned. It gives a high-level idea ('saldo de créditos e plano') but lacks specifics like field names or structure, leaving some ambiguity despite the simple scope.

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 only parameter (api_key) is fully described in the schema with 100% coverage, so the description adds no additional parameter semantics. The schema already explains the key is optional if configured via environment, matching the baseline.

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 information about the user's credit balance and plan, which is a specific verb+resource. This distinguishes it from the sibling lookup_cpf, which is a lookup operation.

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 provides clear context for when to use the tool: when needing quota/plan information. It also notes the authentication prerequisite. It doesn't explicitly discuss alternatives, but no alternative quota tool is listed among siblings.

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