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

With no annotations, the description carries the full burden and does well: it names the validation algorithm, discloses the return contents (validity, normalized IBAN, bank identifier), and even surfaces the per-call cost and payment rail. It stops short of describing failure behavior (error vs. validity=false) or idempotency, which an unannotated tool could usefully state.

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?

Three tight sentences: purpose and algorithm first, then usage guidance, then return shape and cost. Every sentence earns its place with no filler.

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?

No output schema exists, so the description must describe returns, and it does so adequately (validity, normalized IBAN, bank identifier). It does not specify the bank-code format or how invalid input is signaled, leaving a small gap for a validation tool.

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?

The single parameter is already fully documented in the schema ("IR + 24 digits"), so the schema does the heavy lifting. The description adds no format, normalization, or trimming detail beyond what the schema provides, making 3 the appropriate baseline.

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 (validate), a specific resource (Iranian IBAN/Sheba), and the exact method used (ISO 13616 mod-97). It clearly distinguishes itself from the many sibling validators by naming the Iranian IBAN domain and the bank-code return.

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?

Explicitly says to use it "before sending or crediting an Iranian bank transfer," which gives the agent a clear trigger context. It does not name a when-not condition or point at an alternative sibling, so it falls just short of a 5.

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