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

Annotations already declare readOnlyHint=true, openWorldHint=false, and destructiveHint=false, so safety behavior is covered. The description adds useful context that results are based on 暦注の慣行 and gives examples of time-specific fortune, but it does not describe return structure, timezone handling, or other limitations.

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 compact and front-loaded: it states the primary result first, then adds brief examples. Every sentence contributes useful meaning without repetition.

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 one-parameter read-only lookup tool, the description gives enough context to understand the result type and basis. However, because there is no output schema, it could more explicitly describe the return shape or per-time-period structure.

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 description coverage is 100%, and the single date parameter is fully documented with format YYYY-MM-DD and a valid range. The description only says 指定した日の, adding no parameter semantics beyond the schema, so the baseline 3 applies.

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 that the tool returns the rokuyo for a specified date plus good/bad fortune by time period, with concrete examples such as 先勝 and 赤口. It is specific about resource and output content, though it does not explicitly distinguish itself from siblings like get_koyomi_day or search_lucky_days.

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?

Usage is implied by the tool name and the description of returning hourly fortune for a date, but there is no explicit statement of when to use this tool versus alternatives. No exclusions or alternative tools are mentioned.

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