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openephemeris

Open Ephemeris

by openephemeris
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Remote

Interactive Moon Phase Explorer

explore_moon_phase
Read-onlyIdempotent

Get the Moon's phase, illumination, zodiac sign, void-of-course timing, lunar age, next New/Full Moon, and tightest aspects for a chosen date, time, or location.

Instructions

Use this when the user asks 'what's the moon phase tonight', 'is tonight a full moon', 'show me the moon right now', 'what sign is the Moon in', 'is the Moon void of course' — or has no birth data and wants somewhere to start; it needs no arguments. Returns an interactive Moon dial (inline in Claude and ChatGPT; text summary elsewhere): illumination, phase, Moon sign and degree, void-of-course timing, lunar age, days to the next New and Full Moon, and the tightest applying aspects.

CREDIT COST: 3 credits per call (phase + void-of-course + aspects, 1 each).

Input Schema

NameRequiredDescriptionDefault
datetimeNoISO 8601 with a required zone, or local time with `timezone`. Default now.
latitudeNoOptional; for local void-of-course.
timezoneNoIANA zone for a local datetime.
longitudeNoOptional; for local void-of-course.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changedv4.29.0
    • changedInput schema / properties / datetime / description
      Previous value: -"ISO 8601 datetime to query, stating its zone ('2026-03-20T12:00:00Z'), or a local time together with timezone. If omitted, returns the current live moon phase (UTC now)."New value: +"ISO 8601 with a required zone, or local time with `timezone`. Default now."
    • changedInput schema / properties / latitude / description
      Previous value: -"Observer latitude (optional, used for local void-of-course calculations)."New value: +"Optional; for local void-of-course."
    • changedInput schema / properties / longitude / description
      Previous value: -"Observer longitude (optional, used for local void-of-course calculations)."New value: +"Optional; for local void-of-course."
    • changedInput schema / properties / timezone / description
      Previous value: -"IANA timezone (e.g. `America/Chicago`); required when the datetime is naive, ignored otherwise."New value: +"IANA zone for a local datetime."
  2. Addedv4.8.0

TDQS

A4.3/5.0
Behavior5/5

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

Beyond the annotations, the description discloses the credit cost, the return contents, and that it renders an interactive dial inline in Claude and ChatGPT but a text summary elsewhere. These are substantive behavioral details that annotations alone would not provide.

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?

The description is front-loaded with exact user phrasings, then states the return format and cost. Despite listing many trigger examples, each part serves a clear routing or behavioral purpose.

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 zero-required-parameter, read-only Moon-phase tool with no output schema, the description explains when to call it, what it returns, and its credit cost. An agent has enough information to invoke it correctly without needing more structured metadata.

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%, so the four optional parameters are already documented by the schema. The description adds only that no arguments are needed and that it defaults to now, which is useful but does not add much beyond schema semantics.

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

Purpose4/5

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

The description states a specific resource and purpose: current Moon phase, illumination, sign, void-of-course timing, and related lunar data. It distinguishes itself somewhat from birth-data tools by saying it is for users with no birth data, but it does not explicitly differentiate itself from sibling lunar tools such as ephemeris_moon_phase or ephemeris_next_lunar_phase.

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?

It gives clear trigger phrases such as 'what's the moon phase tonight' and 'is the Moon void of course,' and notes that it needs no arguments. However, it does not say when to choose it over sibling Moon tools, so the agent must infer alternative routing.

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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