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

With no annotations provided, the description carries the full burden of behavioral disclosure. It mentions format flexibility (full-width digits, missing hyphens) and that results include romaji, which is useful. However, it does not disclose error behavior, network dependencies, or any side effects. For a read-only lookup this is acceptable but not comprehensive.

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 concise and bilingual, with the primary purpose front-loaded. It avoids unnecessary filler and uses two short sentences per language. Every sentence contributes meaningful information about accepted input or output details.

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 lookup with no output schema, the description provides essential details: input format flexibility and romaji output. It does not describe the full return structure (e.g., whether it returns Japanese address, prefecture, etc.), but the core information is present. Given the tool's simplicity, this is adequate but could be more thorough.

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 parameter is fully documented in the schema. The description adds a bit of nuance about accepted formats (full-width digits, missing hyphens), which partially overlaps with the schema. This adds marginal value but does not significantly exceed the baseline for full coverage.

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 clearly states the tool's purpose: reverse lookup of a Japanese address from a postal code. It specifies the resource (postal code) and the action (getting address). However, it does not explicitly differentiate from the sibling 'search_address', leaving some ambiguity about when to prefer this tool over the alternative.

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 guidance is provided on when to use this tool versus the sibling 'search_address'. The description explains accepted input formats but does not mention any conditions, exclusions, or alternatives. An agent would have to infer usage context 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.