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

No annotations are supplied, so the description carries the full burden, yet it discloses almost no behavior: nothing about the result format, whether matching is case-sensitive or partial-prefix, how many records come back, or what happens when zero companies match. The only behavioral hint is provenance ("Mirrors the RegBase jp-company-lookup actor"), which implies an external data source but adds no operational detail.

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 tight sentences, with the lookup key and its two modes front-loaded before the provenance note. Nothing is redundant and no sentence is wasted.

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 an external-lookup tool with no annotations and no output schema, the description does not say what the response looks like, whether results are paginated or capped, or how failures/no-match cases surface. An agent knows how to call it but not what to expect back.

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?

The description adds real meaning for "query" beyond the schema's generic "Corporate number or company name substring": the 13-digit exactness constraint and the Japanese-or-English language support. However, with only 50% schema coverage, "max_results" is undocumented in both places (no unit, no ceiling, no behavior description), which the description does not compensate for.

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 names a specific verb and resource ("look up a Japanese company") and states the two accepted input forms with enough precision that an agent can distinguish it from the sibling tools (diff, snapshot info, signature verification), which deal with entirely different objects.

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?

It implies when each query mode applies (exact 13-digit number vs. name substring, in Japanese or English), which is useful routing guidance, but there is no explicit statement of when to prefer this tool over alternatives or of any prerequisites. The sibling tools are unrelated, so the practical ambiguity is low.

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