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

No annotations are provided, so the description carries the behavioral disclosure burden. It does well by explaining input normalization, tolerance of street numbers/building names, resolution to town level, and inclusion of Japan Post romaji in results. It could be more explicit about what fields are returned or how ambiguous matches are handled.

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 compact and front-loads the core purpose before describing tolerance and output details. The bilingual repetition is justified for a Japanese-specific tool, but it does add some length.

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?

With no output schema and no annotations, the description reasonably covers the essential behavior: input handling, accepted formats, and that results include romaji. It could be more complete by stating the full returned fields (e.g., postal code, address, romaji), but it gives enough context for an agent to invoke the tool correctly.

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 baseline is 3. The description adds meaningful parameter-level context beyond the schema by explaining that the address parameter tolerates messy input, full-width digits, hyphen variants, and extra address components—information not present in the schema.

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 specific action and resource: 'Look up a Japanese postal code from an address string.' It adds concrete scope details such as tolerating messy input, resolving to town level, and accepting romaji/English, which distinguishes it clearly from the sibling tool lookup_zipcode.

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?

The description provides a clear use case: when you have a Japanese address string and need the postal code. It also clarifies acceptable input variants (romaji, English, full-width digits). It does not explicitly name lookup_zipcode as the alternative for the reverse lookup, so it falls short of a 5.

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