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

Annotations already declare readOnlyHint, openWorldHint=false, and destructiveHint=false. The description adds useful behavioral context beyond those: the official-source verification, the inclusion of substitute and citizens' holidays, and the 366-day maximum span.

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 compact sentences: the first front-loads scope and provenance, the second specifies the parameter modes and limits. No redundant or filler text.

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 read-only list tool with no output schema, the description covers scope, provenance, date range, and parameter selection modes. It does not explain what happens when no parameters are supplied (all parameters are optional) or the return format, which are the remaining gaps.

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 67%, and the schema itself documents start/end formats and year min/max. The description adds meaning beyond the schema by stating the 'year or start+end' selection model and the 366-day maximum span, which is not encoded in the schema.

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 states a specific verb and resource: a list (一覧) of Japanese national holidays, substitute holidays, and citizens' holidays, with provenance (verified against Cabinet Office published values). This clearly separates it from siblings like check_business_day or search_lucky_days without needing their schemas.

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 explains the two supported query modes — by year or by start/end range — and gives the range limits. It does not explicitly say when to prefer this over related tools such as check_business_day, but the context of use is clear.

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