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

Beyond annotations (readOnlyHint, openWorldHint, idempotentHint), the description explains the composite nature, optional parameter behavior, and a specific caveat about government agency responses being correct per Japanese tax law.

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?

Two dense sentences plus a note, front-loaded with key info, no redundancy, every sentence serves a purpose (purpose, use-case, caveat).

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 two parameters, output schema exists, and external API dependencies, the description covers input format, composite behavior, optional parameter, and a critical edge case, making it fully adequate.

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%, so baseline is 3. The description adds value by explaining the number parameter as '13-digit corporate number' and the verify_invoice parameter's effect (triggers invoice.verify) and default false, plus a behavioral note on invoice status.

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 it's a 'one-call composite' that retrieves corporate info and optional invoice registration via two NTA APIs, specifying input (13-digit corporate number) and distinguishing from separate calls to houjin.lookup and invoice.verify.

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?

Explicitly says 'Use when you need both corporate identity and invoice status in one step — saves an extra API call vs calling houjin.lookup + invoice.verify separately,' and adds a behavioral note about government agencies, guiding correct use.

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