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

Adds context beyond annotations: requires INVOICE_APP_ID (with application instructions), notes that registration status cannot be known from model weights and changes daily, and specifies return fields. No contradiction with annotations (readOnlyHint, openWorldHint, idempotentHint).

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?

Well-structured with all necessary information: purpose, returns, prerequisite, critical usage warning, and sibling differentiation. The Japanese sentence adds value for bilingual contexts but could be considered slightly verbose, still earning a high score.

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?

Covers all necessary aspects: purpose, prerequisite (INVOICE_APP_ID), return fields, usage urgency, and differentiation from sibling. With an output schema present (implied by 'returns'), the description is fully 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?

Only one parameter (number) with 100% schema description. The description adds an example format and context, but doesn't provide additional semantic meaning beyond what the schema already offers. Baseline 3 is appropriate.

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 verifies invoice number registration against the NTA public registry API and returns specific fields (registrant name, address, registration date). It also distinguishes itself from sibling invoice.validate by noting 'For offline format checks only, use invoice.validate.'

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 states 'Always call this before trusting any Japanese invoice number' and explains why (registration status changes daily). Also provides an alternative for offline checks (invoice.validate), giving clear when-to-use and when-not-to-use guidance.

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