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

Annotations already declare readOnly, idempotent, non-destructive. The description reinforces this with 'Nothing is sent to the tax authority and no document is created' and adds behavioral context by detailing what is checked (field formats, nfe-specific ncm/cfop and address) and what is not (cross-field/fiscal rules). This exceeds annotation coverage without contradiction.

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 three short paragraphs with the core purpose front-loaded. Each sentence adds value: the summary, the safety reassurance, the specific checks, and the limitation. It is slightly verbose but not padded, and the structure is logical.

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 validation tool with an output schema, the description covers usage context, limitations, and key validation specifics. It doesn't fully enumerate all param requirements or the exact validation rules, but it provides enough for an agent to decide when and why to call it. The presence of an output schema reduces the need to explain return values.

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 has 0% description coverage, so the description must compensate. It references items and recipient_address in the nfe context, implying their significance, and document_type is covered by the enum. However, it doesn't explicitly detail each parameter's format or constraints, leaving some interpretation to the agent. Still, it adds meaningful context beyond the bare 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 the tool validates invoice data against field rules without issuing anything. It distinguishes itself from issue_invoice and specifically mentions the nfe checks (ncm, cfop, recipient address), making its purpose unambiguous.

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?

It explicitly advises calling this before issue_invoice when a field was inferred, and warns that it does not replace issuing since authorizer rules are only checked on transmission. This gives clear when-to-use and when-not-to-use guidance, differentiating it from sibling tools.

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