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

Annotations declare readOnly and openWorld, and the description adds real context beyond them: the three outcome states, the NTA-published dates and difference file provenance, check-digit validation, and the semantic caveat that absent records mean 'unknown' rather than 'not registered'. Return-field detail is partially duplicated by the existing output schema, so it stops short of a 5.

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?

Front-loaded with the question the tool answers, then identifier forms, then result semantics. Dense and mostly waste-free, though the example registration number is repeated from the schema and the result-status sentence is packed tightly.

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?

Only two optional parameters, full schema coverage, a present output schema and safety annotations — and the description still supplies the one thing structured fields cannot: what 'unknown' implies and which population (corporations) is covered. Nothing needed to call or interpret it is missing.

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%, so the baseline is 3; the description goes further by explaining that corporate_number is looked up as 'T' + the 13 digits and that the check digit is validated, which affects how an agent should construct and retry inputs.

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?

Opens with a specific question the tool answers: is this corporation a registered qualified invoice issuer, since when, cancelled/expired. Verb and resource are unambiguous and scope ('Corporations only') is stated. It does not, however, distinguish itself from the sibling invoice_registration_changes, which overlaps with the 'recorded changes' wording in the return description.

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?

'Give number (T...) or corporate_number (13 digits)' tells the agent exactly which identifier forms to supply, and the closing sentence ('A number not seen in the recorded files is unknown, never not registered') sets a critical interpretation rule. No routing guidance versus sibling tools is provided.

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