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

With no annotations, the description carries the full behavioral burden, yet it only hints at return content (region types kelurahan/desa). It says nothing about cardinality (one postal code mapping to multiple regions), error behavior for unknown codes, or whether results are paginated.

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?

It is a single short sentence with no waste, which is good, but its terseness is the problem: a fragment lacking a verb leaves the operation under-specified rather than efficiently explained.

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?

No annotations and no output schema, so the description must convey the return shape. It partially does (regions typed as kelurahan/desa) but omits cardinality and result structure, leaving an agent unable to predict the response for a given code.

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% for the single postal_code parameter (including a 5-digit pattern), so the schema does the heavy lifting. The description adds no syntax or format detail beyond implying the input is a postal code.

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 is a bare noun phrase stating what the tool returns ('Regions (kelurahan or desa) that carry one postal code') rather than a verb+resource. Combined with the name reverse_postal_code, an agent can infer a reverse lookup, but the description itself never states the action or contrasts it with the sibling get_postal_code.

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?

No when-to-use guidance is given, and the obvious alternative get_postal_code (the forward lookup) is never named. The agent must infer the direction of the lookup from the tool name alone.

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