Usno Astronomy

Usno Moon Phases

usno_moon_phases

Read-onlyIdempotent

Moon phases from the US Naval Observatory: the UT date and time of every New Moon, First Quarter, Full Moon and Last Quarter in a year, or the next few phases from a given date. Answers "when is the next full moon", "full moons in 2026", "what phase is the Moon in this week", "date of the new moon in October". Pass a year for the whole year, or a start date (default today) with a count for the next phases.

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "year": 2026
    },
    "name": "usno_moon_phases"
  }
}

Input Schema

Name	Required	Description
`date`	No	Start date YYYY-MM-DD for the next phases from that day. Default today when year is omitted.
`year`	No	Four-digit year, 1800-2050, for every phase in that year (about 50).
`count`	No	How many phases to return from the start date, 1-99. Default 8 (about two lunar months).

Output Schema

Name	Required	Description	Default
`phases`	Yes
`source`	Yes
`returned`	Yes
`time_note`	Yes
`next_new_moon`	No
`next_full_moon`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 11, 2026

TDQS

A4/5.0

Behavior3/5

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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the safety profile is covered. The description adds only the scale of results ('about 50' per year, default 8 phases), which is mildly useful but largely mirrors the schema defaults.

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

Conciseness4/5

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

Front-loaded with the resource and its outputs, followed by concrete example intents, then the usage rule. Tight and well ordered, though the final sentence largely restates what the schema parameters already say.

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?

An output schema exists, so return-format explanation is unnecessary; the description covers both invocation modes, defaults, and the kind of user question it answers. Nothing an agent needs 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.

Parameters3/5

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

Schema coverage is 100% and each parameter already documents format, range, and default. The description restates the year-vs-(date,count) mode split and 'default today' without adding syntax or edge-case detail beyond the schema, so baseline 3 is appropriate.

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?

States a concrete verb+resource (returning USNO moon phase dates/times for New/First Quarter/Full/Last Quarter) and scopes it to a year or a forward window. It is immediately distinguishable from siblings like usno_seasons and usno_solar_eclipses.

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?

The example questions ('when is the next full moon', 'full moons in 2026') and the closing sentence ('Pass a year for the whole year, or a start date with a count') tell the agent exactly which mode to pick. No explicit exclusions or named alternatives, but the trigger conditions are clear.

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

All Usno Astronomy tools Inspect

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