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

Annotations already declare readOnlyHint=true and idempotentHint=true. The description adds that it never changes the document, which is redundant but consistent. It doesn't disclose any additional behaviors like error conditions or rate limits, but with annotations covering the safety, a score of 3 is appropriate.

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?

Two sentences with no filler. The key information (read-only) is front-loaded. Perfectly concise.

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 an output schema, so return values are covered. However, the parameters are insufficiently explained: 'document_type' is required but its purpose is not stated. Given the low schema coverage, the description fails to make the tool callable correctly.

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 description mentions 'access key' but does not explain the purpose of 'document_type' which is a required enum (nfse, nfe). With 0% schema description coverage, the description should have explained both parameters, but it only covers access key, and even that is not elaborated beyond naming it.

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 states a clear verb ('look up') and resource ('invoice's current status') with a specific access key. It is distinct from sibling tools like cancel_invoice or issue_invoice by being read-only.

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 explicitly says 'Read-only: it never changes the document,' which signals that this tool is for status checks only and not for modifications. However, it does not explicitly mention alternative tools, so it's slightly less explicit than ideal.

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