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

No annotations exist, so the description carries the full burden, and it does disclose meaningful traits: the Luhn validation method, the return contents, and the per-call cost/currency. It stops short of error behavior or input-format edge cases, but the pricing and result disclosure is unusually strong.

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 tightly packed sentences: purpose and mechanism first, usage trigger second, return/cost third. No filler, nothing repeated.

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 no output schema and no annotations, the description compensates by naming the return values (validity, masked number, bank name) and the cost. For a simple single-param validator this is nearly complete; only error/tie-break behavior is unstated.

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 has 100% schema description coverage ("16-digit Iranian bank card number"), so the schema already carries the parameter meaning. The description adds nothing beyond the schema about format or constraints. Baseline 3 applies when schema does the lifting.

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) and resource (Iranian bank card number / PAN), plus the mechanism (Luhn check digit) and the distinguishing output (issuing bank). This clearly separates it from the sibling validators like fa_validateSheba or fa_validateNationalId.

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?

"Use it before charging a card or accepting card details from a customer" gives a concrete when-to-use trigger. It does not name or exclude sibling alternatives, but the context is clear enough to route an agent correctly.

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