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

Annotations already declare readOnly/idempotent/non-destructive/no open world, so the safety profile is covered. The description adds real value beyond that: the scope is Romanian banks (plus State Treasury), it discloses which checks are performed, and it signals a free tier. It stops short of saying what an invalid IBAN returns (error vs. negative result) and whether the account itself is verified.

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?

One sentence, front-loaded with the decision the agent is making, zero filler. 'Free' is the only compressed extra and it is still useful.

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?

With one required param, no output schema and full annotation coverage, the description covers purpose, scope, checks performed and cost. The remaining gap — what the caller gets back on a bad IBAN — is modest but real given there is no output schema to fall back on.

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 single 'iban' parameter is documented with an example plus 'spaces allowed'. The description adds no format nuance (e.g., country prefix requirement, whitespace normalization) beyond what the schema already says, so 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?

Specific verb+resource: it validates an IBAN, checks length and check digits, and returns the Romanian bank (or State Treasury) name. That is concrete and distinguishable from every sibling (invoice/Saft validators, fx_rate, lookup_company) without opening a 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?

States the trigger context explicitly — 'before putting an IBAN on an invoice or paying to one' — which is a clear when-to-use. It does not name any exclusion or alternative, though no sibling obviously overlaps, so the gap is minor.

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