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

Goes well beyond the readOnlyHint/idempotentHint annotations by explaining the anti-fraud ladder, why limits vary per payer, and the acao error taxonomy with retry behavior. It also warns that approval can still fail for other reasons, which is non-obvious behavioral context.

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 longer than average, but every section earns its place: return value, usage conditions, behavioral reasoning, input format, and error handling. The most decision-relevant information is front-loaded in the first sentence.

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?

For a single-parameter read-only tool with no output schema, it fully covers units, document formats, error cases, retry guidance, and follow-up behavior. An agent has enough information to invoke it correctly and interpret the result.

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%, including the digits-only CPF/CNPJ pattern, so the baseline is 3. The description reinforces the digits-only rule but does not add meaningful parameter semantics beyond what the schema already provides.

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 specific verb and resource: it returns how much a CPF/CNPJ taxpayer can move through a PIX charge right now, in cents. It also explicitly says read-only and that no charge is created, which separates it from mutation siblings like lunium_create_pix_charge.

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 when-to-use guidance: call it before lunium_create_pix_charge when the payer is new or the amount is not trivial. It also lists exclusions: don't use it as a document-validity check and don't treat a high limit as approval.

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