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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful scope context beyond them: it performs format/structure validation only and explicitly does not perform ownership, registry or fraud clearance, which is exactly the boundary an onboarding agent needs.

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, zero filler. The capability statement is front-loaded and the scope caveat follows immediately, earning each clause.

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?

An output schema exists, so return-value detail is correctly omitted, and the scope limitation is stated. The one gap is that all four parameters are optional and the description never says whether any subset (or none) may be supplied or how partial input is handled.

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%, so the four parameters are already documented individually (including 'BE mod-97' and 'UK company number'). The description restates the same field list without adding format, accepted-value, or partial-submission guidance, so the baseline 3 applies.

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 ('Check supplied IBAN, LEI, Belgian VAT and UK company-number fields') and the phrase 'in one result' distinguishes it from the single-identifier siblings like iban_check, lei_check and vat_mod97_check. An agent can tell this is a bundled multi-field validator without opening any schema.

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?

'Structural checks only; no ownership, registry or fraud clearance' is an explicit when-not boundary that tells the agent this tool cannot satisfy due-diligence screening. However, it never names an alternative for identifier-by-identifier checks, so the 'when to use this vs the individual siblings' decision is left to inference.

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