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 discloses the validation mechanism (recomputing the check digit), the return contents (validity and parsed digits), and even the cost model ($0.005 per call, USDC on Base). It omits error/edge behavior for malformed input, which keeps it from a 5.

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?

Front-loaded with purpose, then usage, then return, then cost – the reader gets the essentials first. It is slightly dense with four clauses, but every clause carries information, so little is wasted.

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 single-parameter validation tool with no output schema, the description supplies purpose, format, usage context, return values, and cost. Nothing an agent needs in order to call it correctly 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 description coverage is 100% and the schema already documents 'value' as a 12-digit economic code. The description repeats the same 12-digit framing without adding syntax, normalization, or format nuance beyond the schema, so baseline 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?

States a specific verb (validate) and resource (Iranian economic code) and glosses it as the 12-digit taxpayer identifier, which distinguishes it from sibling validators like fa_validateNationalId or fa_validateCompanyId at a glance.

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 names the context of use – validating a tax identifier on an Iranian invoice or supplier record – which gives the agent a clear trigger. It stops short of naming when NOT to use it or which sibling to prefer, so it is clear context without exclusions.

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