47都道府県の名称一覧を取得

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

With no annotations provided, the description carries the burden. It clarifies the tool is read-only (returns a list) and discloses a subtle behavioral trait: topology sharing is only guaranteed within a single call, so using the full list prevents boundary misalignment. It does not mention any error conditions or performance, but for a static list that is acceptable.

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 description is front-loaded with the purpose, followed by usage guidance and rationale. All sentences earn their place, but the explanation about topology sharing is relatively lengthy for a simple list tool, making it slightly less concise than it could be. Still highly structured and informative.

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?

Given the tool's simplicity (no params, no output schema), the description fully covers its purpose, return format, and integration with a sibling tool. It even addresses an edge-case risk (omissions and boundary misalignment) and provides a complete solution. Nothing essential 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?

The tool has zero parameters and schema coverage is 100%, so the baseline is 4. The description explicitly states 'no parameters', reinforcing the schema but adding no additional semantics. Nothing else is needed.

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 uses a specific verb ('返す' / returns) with a clear resource (47 prefecture official names as an array) and states it has no parameters. It distinguishes itself from sibling tools by being the canonical list source, not a search or geocoding tool.

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?

Provides explicit when-to-use guidance: pass this tool's result directly to addresses when creating a Japan map via get_address_locations. It also tells the agent not to rely on LLM memory or piecemeal fetching, explaining the topology sharing risk. This clearly frames the tool as the correct choice over other address-related tools.

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