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

With no annotations, the description carries the full burden and does reasonably well: it discloses the validation mechanism (check-digit recomputation), the return payload (validity, normalized code, province), and the cost model ($0.005 per call, USDC on Base). It omits edge-case behavior such as how malformed or non-Iranian input is reported, which keeps it out of 5 territory.

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 short sentences, front-loaded with the purpose and followed by usage, returns, and pricing. Every clause carries information; the pricing note is dense but relevant for a paid endpoint.

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 supplies the essentials: what is validated, what comes back, and the cost. Only edge-case and input-format details are absent, which is a minor gap at this complexity level.

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 '10-digit postal code', which the description essentially restates. The mention of a 'normalized code' in the return hints that input formatting is tolerated, but no syntax rules (spaces, dashes, Persian vs Latin digits) are given, so it adds little 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 (Validate) and resource (Iranian postal code), with the mechanism (recomputing its check digit) and the exact identifier (کد پستی, the 10-digit code). Among siblings like fa_validateBankCard, fa_validateNationalId and fa_validateSheba, the resource name alone routes the agent unambiguously.

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 using a postal code for delivery or address validation' gives a clear trigger context. It stops short of naming alternatives or stating when-not-to-use (e.g. for non-Iranian codes), so it is clear but not exhaustive.

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