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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuinely new behavioral context: the data is checked against 国立天文台・内閣府 published values and covers 1926–2080, telling the agent how authoritative the results are and where the boundary lies.

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?

A single front-loaded sentence with the subject ('指定した日の暦') first, followed by a compact enumeration and then provenance. The dense item list is justified because it doubles as the return-value inventory in the absence of an output schema.

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?

With no output schema, the enumeration of returned fields is exactly what the agent needs to judge whether this tool answers its question, and the stated year range and data provenance close the remaining gaps. Only explicit sibling routing is missing.

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?

One parameter with 100% schema description coverage — the schema already specifies the YYYY-MM-DD format and the 1926-01-01〜2080-12-31 bounds. The description only restates that range in prose and adds no format or edge-case guidance beyond it, 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 makes clear this returns the full calendar record for a single given date, and enumerates the specific contents (和暦, 旧暦, 六曜, 二十四節気, 月齢, 祝日, 九星, etc.), which distinguishes it from narrower siblings like get_moon_phases or get_solar_term_times. It never states an explicit verb ('returns'/'gets'), but the resource and scope are unambiguous.

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 only implied: the presence of the date parameter and the breadth of the returned fields suggest 'call this when you need a single day's complete almanac.' There is no explicit when/when-not guidance and no routing to siblings such as get_moon_events or get_rokuyo_hours for the specialized data it overlaps with.

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