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Moon Phases

usno.astronomy.moon_phases
Read-onlyIdempotent

Retrieve all moon phase dates for any year—New Moon, First Quarter, Full Moon, Last Quarter—with precise UTC timestamps from the US Naval Observatory.

Instructions

Get all moon phase dates for a year — New Moon, First Quarter, Full Moon, Last Quarter with exact UTC timestamps. ~50 phases per year. Source: US Naval Observatory (canonical astronomical authority, US Gov public domain).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
yearNoYear for moon phases (default: current year, e.g. 2026)

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultNoTool response payload. Shape varies per tool — consult the tool description and inputSchema. May be an object, array, string, or number depending on the upstream provider response.
errorNoPresent only when the call failed. Includes error code, message, request_id, and any provider-specific extras.
Behavior5/5

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

Disclosures beyond annotations include exact phases, ~50 per year, exact UTC timestamps, and canonical source (US Naval Observatory, public domain). No contradictions.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two efficient sentences. First sentence defines core function; second adds authoritative context. No filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple tool with one optional parameter and output schema, description covers all needed info: output content, frequency, source reliability.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Only one parameter (year), schema coverage 100%. Description adds no extra meaning beyond schema's default and range. Baseline 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states it retrieves all moon phase dates for a year, listing the four phases and source authority, distinguishing it from sibling tools like seasons or sun_moon.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Implicitly clear: use to get moon phases for a year. Source authority is noted. Does not explicitly mention alternatives or when not to use, but context is adequate.

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

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