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

With no annotations, the description carries the full burden, and it does meaningful work: it discloses the validation algorithm (check-digit recomputation, not a registry lookup), states what is returned (validity plus parsed digits), and discloses cost ($0.005 per call, USDC on Base). It stops short of describing behavior on malformed or non-10-digit input.

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, front-loaded with purpose, then usage, then return value and pricing. No filler; every sentence carries information an agent would otherwise have to infer.

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 covers purpose, usage context, return contents, and cost. The only gap is edge-case behavior (e.g., input that is not 10 digits), which is minor for a stateless validation call.

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 description coverage is 100% and the single parameter is documented as a '10-digit national ID', so the schema already does the heavy lifting. The description's mention of check-digit recomputation adds method context but no new syntax or format detail for the argument itself.

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 national ID / کد ملی) plus the mechanism (recomputing its check digit). Against siblings like fa_validateBankCard, fa_validateSheba and fa_validatePostalCode, the resource is unambiguous, so an agent can select it without opening the 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?

Gives an explicit usage context: 'Use it before accepting an identity number from a form, a customer, or an API payload.' It does not name a when-not condition or a competing sibling, but the tool's scope is narrow enough that no alternative is plausible, so this is clear context rather than full routing guidance.

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