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

With no annotations, the description carries the full behavioral burden. It usefully discloses the internal dependency (wilayah table lookup) and a privacy trait ('it is never logged'), which is real value beyond the schema. However it omits error behavior for malformed NIKs and whether the call is purely read-only.

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?

Two tight sentences with the core purpose front-loaded and the privacy note placed second where it belongs. The 'Send the NIK in the JSON body' clause is mildly redundant with a required, 100%-documented parameter, but it is not wasteful enough to hurt.

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 tool with no annotations and no output schema, the definition is only partially complete: it never indicates what comes back (a validity verdict? the resolved region name?), which is exactly the gap an absent output schema leaves for the description to fill.

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%, so the single parameter is already documented. The description repeats the 16-digit framing and adds that it goes in the JSON body, but adds no format detail — and the schema's maxLength of 32 is left unexplained against the stated 16-digit requirement.

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?

The description gives a specific verb+resource ('Checks the structure of a 16-digit NIK') plus the secondary behavior (region-digit lookup in the wilayah table). That is enough to separate it from generic getters, but it never contrasts itself with the closest sibling get_wilayah, which also touches region data.

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?

Usage is only implied by the stated purpose — an agent can infer 'use this to validate a NIK' but there is no explicit when-to-use, no note on when to prefer get_wilayah or reverse_postal_code, and no mention of what an invalid NIK produces.

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