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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint. The description adds that the tool uses the NTA official API (external dependency) and provides authoritative data not available from model weights, enriching the behavioral context without contradiction.

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 extremely concise: two sentences plus a bold usage note. Front-loaded with action and output, then critical guidance. No redundancy or filler.

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 single-parameter lookup tool with full schema coverage, annotations, and an output schema, the description fully covers the purpose, source, and usage context. It explains the output fields and warns about model weight limitations, making it complete.

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 coverage is 100% with a Japanese description of the number parameter. The tool description adds the English equivalent ('13 digits') and reinforces the format, providing extra clarity for bilingual users beyond the schema alone.

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?

Description clearly states the tool looks up a Japanese corporate number (13 digits) and returns company name, address, kind, and status via the official NTA API. It distinguishes itself from siblings like company.fullProfile by focusing specifically on corporate number lookups.

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 explicitly says 'Call this for authoritative company info' and warns that corporate registry data cannot be recalled from model weights, providing clear when-to-use guidance. It does not explicitly mention alternatives but the purpose is sufficiently distinct.

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