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

With no annotations, the description carries the full burden and discloses important traits: deterministic offline validation, no network call, no third-party dependency, and per-call pricing. It still does not describe invalid-input behavior or the exact response shape.

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-loads the when-to-use condition and then packs the relevant validation, runtime, and cost details without filler. Every sentence contributes useful selection or invocation context.

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 simple one-parameter validation tool with no annotations or output schema, it provides enough context to call correctly: scope, checks performed, offline behavior, and cost. A fuller definition would clarify the returned fields or error handling.

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 spaces and lowercase are accepted. The description reinforces that only one IBAN is checked at a time, but adds no syntax or format details beyond the schema.

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: validates one IBAN. It names the exact checks performed, including country, length, mod-97, SEPA status, and account split, so it is clearly distinct from sibling validators like util_vat or red_email_check.

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?

Gives a clear usage condition: use before attempting payment, and for cleaning account lists one at a time. It does not explicitly name alternatives or exclusions, so it stops short of a full when/when-not guide.

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