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Natal Chart Lab MCP

Natal Chart Lab MCP

by xucheng2024
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

Natal Chart Lab MCP server

An MCP server that gives AI assistants accurate astrology and sky data: where the Sun, Moon and planets are on the tropical zodiac, the signs in a birth chart, retrograde periods with shadow dates, and Moon phases.

It is a thin client for the free, keyless Natal Chart Lab astrology API. Positions come from Astronomy Engine and are checked against NASA JPL Horizons (largest difference at 50 test points is 19.5 arcseconds, well under a hundredth of a degree). No API key, no sign-up, no personal data stored.

Tools

Tool

What it returns

get_current_sky

Sun, Moon and planet signs and degrees now; the Moon's phase, illumination, next sign change and void-of-course windows for seven days; which planets are retrograde or in shadow

get_planet_positions

Longitude, sign, degree, daily speed and retrograde flag for every body at any UTC time, 1800–2200

get_birth_placements

Sun, Moon and planet signs for a local birth date, clock time and UTC offset (no rising sign or houses; see the birth chart calculator for those)

get_retrogrades

Retrogrades of Mercury–Pluto in a date range with station times, signs, degrees and pre/post-shadow dates (1950–2050)

get_moon_phases

New Moons, quarters and Full Moons in a date range with sign, degree, distance and eclipses (1950–2050)

Example questions it answers: "Is Mercury retrograde right now, and when is the next one?", "What sign is the Moon in, and is it void of course?", "I was born 4 July 1990 at 9:30 in New York. What are my Sun, Moon and Venus signs?", "List the full moons in 2027 and their signs."

Related MCP server: Astral MCP

Install

Requires Node.js 18 or later.

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "natalchartlab": {
      "command": "npx",
      "args": ["-y", "natalchartlab-mcp"]
    }
  }
}

Claude Code

claude mcp add natalchartlab -- npx -y natalchartlab-mcp

Cursor, Windsurf, VS Code and others

Use the same command, npx -y natalchartlab-mcp, as a stdio server.

Data and accuracy

  • Tropical zodiac; apparent geocentric positions on the true ecliptic of date.

  • Mean North Node and mean Black Moon Lilith.

  • Retrograde and Moon phase tables are CC BY 4.0 and also published as datasets (retrogrades, Moon phases).

  • Full method: natalchartlab.com/methodology.

Set NATALCHARTLAB_URL to point the server at another deployment of the same API.

Development

npm install
npm test
npm run build

Licence

MIT. Data from Natal Chart Lab.

Available Tools

5 tools
get_birth_placementsBirth chart planet signsA
Read-only

Sun, Moon and planet signs for a local birth date and clock time. Give the UTC offset that was in force at the birth (including daylight saving). Does not compute the rising sign or houses, which need the birth place; the result links to the free full calculator.

Inputs: date (required), time (required), utc_offset (required).

get_current_skyCurrent skyA
Read-only

The sky right now: tropical zodiac sign and degree of the Sun, Moon and planets, the Moon's phase, illumination, next sign change and void-of-course windows for the next seven days, and which planets are retrograde or in shadow. Times are UTC.

Inputs: no named parameters.

get_moon_phasesMoon phasesA
Read-only

New Moons, first quarters, Full Moons and last quarters in a date range, with the UTC time, zodiac sign and degree, Earth–Moon distance and any eclipse. Covers 1950–2050. Defaults to the next 60 days.

Inputs: to, from, phase.

get_planet_positionsPlanet positions at a timeA
Read-only

Tropical zodiac positions (longitude, sign, degree, daily speed, retrograde flag) of the Sun, Moon, Mercury–Pluto, mean North Node and mean Black Moon Lilith at a UTC instant between 1800 and 2200. Apparent geocentric, checked against NASA JPL Horizons.

Inputs: time.

get_retrogradesRetrograde periodsA
Read-only

Retrograde periods of Mercury through Pluto overlapping a date range, with station retrograde and direct times, signs and degrees, and pre-shadow and post-shadow dates. Covers retrogrades beginning 1950–2050. Defaults to the next 12 months.

Inputs: to, from, planet.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

Loading tool schema changelog…

    Deploy Server
    One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

    TDQS

    A4.1/5.0

    Scored across 5 tools

    Disambiguation4/5

    Each tool has a distinct astrological focus, but get_current_sky overlaps with get_planet_positions for current positions and with get_moon_phases for current lunar phase. The descriptions mostly clarify the boundaries through scope and extra data, so confusion is limited but possible.

    Naming Consistency5/5

    All five tools use the same get_ + noun-phrase pattern: get_current_sky, get_planet_positions, get_moon_phases, get_birth_placements, get_retrogrades. The convention is predictable and easy to scan.

    Tool Count5/5

    Five tools is well scoped for an astrology calculation server, with each tool covering a coherent calculation family. There is no obvious bloat or thin single-purpose surface.

    Completeness3/5

    The set covers planetary positions, lunar phases, retrogrades, current sky, and birth placements, but it explicitly omits houses and rising signs, which are core to a full natal chart. Aspects and broader chart calculations are also absent, though the external calculator link provides a partial workaround.

    Maintenance

    ActivityMaintained
    ResponsivenessNo recent community issues

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