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

With no annotations, the description carries the behavioral burden and usefully discloses that the tool is paid ($0.0029), lists the validation layers, describes the return as pass/fail with checks and issues, and states country coverage. It does not discuss latency or authentication, but for a simple read-only validator those omissions are minor.

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 compact and front-loaded: cost first, then purpose and checks, then return behavior and coverage. Every phrase contributes useful information without 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 validator with no output schema, the description is complete enough: it states the checks performed, the pass/fail return shape, country coverage, and price. Nothing essential for correct invocation 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%: the single iban parameter is fully documented with an example and note that spaces are allowed. The description does not add further parameter syntax or format details, so the baseline of 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?

The description gives a specific verb and resource ("Validate an IBAN") and enumerates concrete checks: ISO 13616 structure, country registration, length, and MOD 97-10 checksum. It also states scope ("Covers 50 countries"), which distinguishes it from generic checksum siblings like mod97_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?

The description implies the tool should be used for IBAN validation and notes the 50-country coverage limitation, but it does not explicitly route the agent away from siblings such as mod97_check or luhn_check. There is no explicit when-to-use/when-not guidance beyond the purpose statement.

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