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

Annotations already establish that this is a read-only, idempotent, closed-world, non-destructive operation. The description adds useful behavioral context by saying it returns official English and Romanian text, a plain-English fix, and UBL field location, and that it is free, though it does not discuss unknown rule IDs or limits.

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 a single front-loaded sentence that leads with the usage trigger and then enumerates the useful return content. There is no filler or repetition.

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 one-parameter lookup tool with no output schema, the description sufficiently explains what the tool returns and why an agent would call it. Annotations cover safety traits and the schema fully documents the only parameter.

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 coverage is 100% and the schema already explains that rule_id comes from findings[].rule or an ANAF error message. The description adds value by showing several concrete rule ID formats across ANAF, Romanian, and Peppol families, which helps an agent recognize valid input beyond the single schema example.

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 specific verb and resource: explaining a named e-invoice rule, including official text, a plain-English fix, and the UBL field location. It clearly distinguishes this lookup/explanation tool from sibling validation and fixing tools such as validate_invoice and fix_invoice.

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 gives a clear trigger condition: use when ANAF SPV, a Peppol access point, or a validation report names a rule and you need to understand or fix it. It does not explicitly state when not to use it or name a specific alternative, so it falls short of a full 5.

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