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

Annotations already declare read-only, non-destructive, closed-world behavior. The description adds genuinely new context: the data is cross-checked against the National Astronomical Observatory's official almanac, timestamps are JST to the second, the supported year range is 1926–2080, and a start/end window may not exceed 366 days.

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?

Three short sentences, front-loaded with what is returned, then how to scope it, then a provenance note. No filler and no repetition of the title.

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?

There is no output schema, so the description carries the burden of describing the result, which it does at a high level (a list of the four phase instants, JST, second precision). The exact response shape (e.g. grouping by month, field naming) is left unstated, but nothing needed to call it correctly 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?

Schema coverage is only 67% — the year parameter has no schema description at all — and the description compensates by giving its range (1926–2080). It also adds a constraint not present anywhere in the schema: start/end spans are capped at 366 days. It does not state whether year and start/end are mutually exclusive, which is a remaining gap.

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?

States a specific resource (the exact instants of new, first-quarter, full and last-quarter moon) with precision and timezone, so an agent knows exactly what comes back. It does not explicitly distinguish itself from similar siblings such as get_moon_events or get_sun_moon_times, so the sibling differentiation is only implicit.

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?

The description explains the two query modes (year, or start+end up to 366 days), which is real usage guidance. However, it never says when to prefer one mode or why an agent would choose this tool over get_moon_events/get_sun_moon_times, and there are no exclusions.

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