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

With no annotations, the description carries the behavioral burden. It clearly implies a read-only listing operation and describes the conditional return content, but it does not cover error behavior, return format details, or any rate/auth considerations.

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?

The definition is a single efficient sentence with no wasted wording. The default behavior is front-loaded and the conditional sido behavior follows naturally.

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 simple one-parameter listing tool with full schema coverage and no output schema, the description provides enough information to invoke it correctly. It reasonably explains both output modes, though it could be slightly more explicit about the returned structure.

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?

The input schema already has 100% description coverage for the single optional sido parameter. The tool description adds meaning by clarifying that supplying sido switches the output from a sido list to that sido's si/gun list, which goes slightly beyond the schema text.

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 states a clear verb and resource: it returns a list of supported sido regions, or si/gun regions when a sido is supplied. This makes the tool's scope easy to distinguish from siblings, though it does not explicitly name or contrast those siblings.

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?

It explains the two operational modes: omit sido to get the top-level region list, or provide sido to get its subregions. However, it does not state when to choose this tool over alternatives such as local_currency_for_region, so usage guidance is mostly implied.

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