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astrology-mcp

by intellecat
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TypeScript

Astrology MCP Server

A Model Context Protocol (MCP) server that provides astrological natal chart calculations. Built with TypeScript and the MCP SDK, this server enables AI assistants to calculate and interpret astrological birth charts based on date, time, and location.

🌟 Now powered by @swisseph/node - Using the Swiss Ephemeris calculation engine for highly accurate astronomical calculations.

Features

  • Accurate Calculations - Powered by Swiss Ephemeris for high precision.

  • Complete Natal Charts - Detailed planet positions, houses, aspects, and chart angles.

  • Flexible Location - Support for coordinates or city names (free geocoding).

  • Multiple House Systems - Placidus, Koch, Whole Sign, and more.

  • Modern Stack - TypeScript, Zod validation, and latest MCP SDK.

Related MCP server: Swiss Ephemeris MCP Server

Quick Start

You can run the server directly using npx without installing anything:

npx -y @astrologer/astrology-mcp

Configuring with you MCP client

Standard config works in most tools.

{
  "mcpServers": {
    "astrology": {
      "command": "npx",
      "args": ["-y", "@astrologer/astrology-mcp"]
    }
  }
}

Manual Installation (From Source)

If you want to modify the code or run from source:

git clone https://github.com/intellecat/astrology-mcp.git
cd astrology-mcp
npm install
npm run build

Dependencies

Runtime

  • @modelcontextprotocol/sdk - Latest MCP SDK

  • @swisseph/node - Swiss Ephemeris calculation engine (high precision)

  • luxon - Timezone and date handling

  • node-geocoder - Location to coordinate conversion

  • zod - Schema validation

Development

  • typescript - TypeScript compiler

  • @types/node - Node.js type definitions

  • @types/node-geocoder - node-geocoder type definitions

  • @types/luxon - Luxon type definitions

Usage

Building

npm run build

Running the Server

npm start

Development Mode

npm run dev

Testing

Run the test script to verify the horoscope calculations:

npm test

MCP Tools

1. astrology_calculate_natal_chart

Calculate a complete natal chart based on birth data.

Parameters:

  • datetime (object, required): Birth date and time

    • year (number): Year (e.g., 1990)

    • month (number): Month (1-12, where 1=January, 12=December)

    • day (number): Day of month (1-31)

    • hour (number): Hour in local time (0-23)

    • minute (number): Minute (0-59)

  • location (object or string, required):

    • As object: {latitude: 40.7128, longitude: -74.0060}

    • As string: "New York, USA"

  • houseSystem (string, optional): House system to use (default: "Placidus")

Returns:

{
  "planets": [
    {
      "name": "Sun",
      "sign": "Taurus",
      "degree": "24° 39' 24\"",
      "longitude": 84.6567,
      "house": 9,
      "isRetrograde": false
    }
  ],
  "houses": [
    {
      "number": 1,
      "sign": "Virgo",
      "degree": "19° 27' 38\"",
      "cuspDegree": 169.4606
    }
  ],
  "aspects": [
    {
      "point1": "Sun",
      "point2": "Moon",
      "aspect": "Trine",
      "aspectLevel": "Major",
      "orb": 5.85,
      "orbUsed": 7
    }
  ],
  "chartAngles": {
    "ascendant": {
      "sign": "Virgo",
      "degree": "19° 27' 38\"",
      "longitude": 169.4606
    },
    "midheaven": {
      "sign": "Gemini",
      "degree": "17° 46' 33\"",
      "longitude": 77.7759
    },
    "descendant": {
      "sign": "Pisces",
      "degree": "19° 27' 38\"",
      "longitude": 349.4606
    },
    "imumCoeli": {
      "sign": "Sagittarius",
      "degree": "17° 46' 33\"",
      "longitude": 257.7759
    }
  },
  "sunSign": "Taurus",
  "birthData": {
    "datetime": {
      "year": 1990,
      "month": 5,
      "day": 15,
      "hour": 14,
      "minute": 30
    },
    "location": "New York, NY, USA",
    "latitude": 40.7128,
    "longitude": -74.006,
    "houseSystem": "Placidus"
  }
}

2. astrology_get_coordinates

Convert a location string to geographic coordinates.

Parameters:

  • location (string, required): Location in format "City, Country" (e.g., "London, UK")

Returns:

{
  "latitude": 51.5074,
  "longitude": -0.1278,
  "formattedAddress": "London, Greater London, England, UK"
}

Example Usage with MCP Client

Example 1: Calculate natal chart with coordinates

{
  "tool": "astrology_calculate_natal_chart",
  "arguments": {
    "datetime": {
      "year": 1990,
      "month": 5,
      "day": 15,
      "hour": 14,
      "minute": 30
    },
    "location": {
      "latitude": 40.7128,
      "longitude": -74.0060
    }
  }
}

Example 2: Calculate natal chart with city name

{
  "tool": "astrology_calculate_natal_chart",
  "arguments": {
    "datetime": {
      "year": 1995,
      "month": 12,
      "day": 25,
      "hour": 8,
      "minute": 0
    },
    "location": "Paris, France",
    "houseSystem": "Whole Sign"
  }
}

Example 3: Get coordinates for a location

{
  "tool": "astrology_get_coordinates",
  "arguments": {
    "location": "Tokyo, Japan"
  }
}

House Systems Supported

The server supports various house systems including:

  • Placidus (default)

  • Koch

  • Equal

  • Whole Sign

  • Campanus

  • Regiomontanus

  • And more supported by the Swiss Ephemeris library

Technical Details

Date Format

  • Month is 1-12 (1 = January, 12 = December)

  • Hour is in 24-hour format (0-23)

  • All times are in local time for the birth location

Coordinate Format

  • Latitude: -90 to 90 (negative for South)

  • Longitude: -180 to 180 (negative for West)

Zodiac System

  • Uses tropical zodiac (aligned with seasons)

  • Degrees are measured from 0° Aries

Astrological Information Provided

Planets

Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, North Node (Mean Node), Chiron

Chart Points

  • Ascendant (AS) - Rising sign

  • Midheaven (MC) - Medium Coeli

  • Descendant (DS) - Opposite Ascendant

  • Imum Coeli (IC) - Opposite Midheaven

Aspects

Automatically calculates aspects between all planets with configurable orbs:

Major Aspects:

  • Conjunction (0°, orb: 10°)

  • Sextile (60°, orb: 6°)

  • Square (90°, orb: 8°)

  • Trine (120°, orb: 8°)

  • Opposition (180°, orb: 10°)

Minor Aspects:

  • Semi-Sextile (30°, orb: 3°)

  • Semi-Square (45°, orb: 3°)

  • Sesquiquadrate (135°, orb: 3°)

  • Quincunx (150°, orb: 3°)

License

AGPL-3.0

Migration to Swiss Ephemeris

This server has been migrated from circular-natal-horoscope-js to @swisseph/node for improved accuracy. The Swiss Ephemeris is the industry standard for astronomical calculations in astrology, providing:

  • Higher precision planetary positions (accurate to arcminutes)

  • Reliable retrograde detection

  • Extensive support for asteroids and minor bodies

  • Industry-standard calculations used by professional astrologers

See MIGRATION_NOTES.md and compare-libraries.ts for migration details and accuracy comparisons.

Credits

Built with:

Available Tools

2 tools
astrology_calculate_natal_chartA
Read-onlyIdempotent

Calculate a complete natal chart (birth chart) based on date, time, and location. Returns detailed astrological information including: planetary positions in zodiac signs and houses with exact degrees, all 12 houses with their cusps, chart angles (Ascendant/Rising, Midheaven, Descendant, Imum Coeli), and major aspects between planets with orbs. Supports multiple house systems.

ParametersJSON Schema
NameRequiredDescriptionDefault
datetimeYes
locationYes
houseSystemNo

TDQS

A3.9/5.0
Behavior3/5

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

Annotations already indicate idempotent and read-only behavior. The description adds no contradictory information but also does not elaborate on aspects like input validation, potential errors, or calculation caveats. It is adequate but minimal.

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?

The description front-loads the main action and uses a bulleted list for return values. It is informative but slightly verbose; could be trimmed without losing content.

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

Completeness4/5

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

Given the complexity of natal chart calculation and no output schema, the description provides a solid overview of what is returned. It covers planetary positions, houses, angles, and aspects, but could specify aspect types or degree precision.

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

Parameters4/5

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

Despite 0% schema description coverage at the top level, the description adds meaning for the main parameters (datetime, location, house system). It clarifies location can be coordinates or city string, and house system is configurable. This compensates for missing schema descriptions.

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?

The description clearly states the tool calculates a natal chart based on date, time, and location, and lists specific outputs (planetary positions, houses, angles, aspects). It distinguishes from the sibling tool astrology_get_coordinates, which is for coordinate lookup.

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

Usage Guidelines3/5

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

The description does not provide explicit guidance on when to use this tool versus alternatives. It mentions support for multiple house systems but lacks context about when not to use or prerequisites.

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

astrology_get_coordinatesA
Read-onlyIdempotent

Convert a location string (city, country) to geographic coordinates (latitude, longitude) using OpenStreetMap geocoding. Useful for obtaining coordinates before calculating a natal chart when only the city name is known.

ParametersJSON Schema
NameRequiredDescriptionDefault
locationYesLocation in format 'City, Country' (e.g., 'London, UK')

TDQS

A4.2/5.0
Behavior4/5

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

The description adds information beyond annotations (readOnlyHint, idempotentHint) by specifying the geocoding service (OpenStreetMap). It does not contradict annotations. A score of 4 reflects that while annotations already indicate safety, the description provides useful context about the external dependency.

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 two sentences with no wasted words. The first sentence states the core action, and the second provides the use case. It is front-loaded and gets straight to the point.

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

Completeness4/5

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

Given the simplicity of this tool (1 parameter, no output schema), the description adequately covers what it does and why it is used. However, it could be slightly more explicit about the return format (e.g., 'returns latitude and longitude as numbers'). Still, the agent can infer from the name and use case.

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?

The input schema already provides 100% description coverage for the single parameter 'location', including the format 'City, Country'. The description restates the conversion purpose but does not add significant new parameter semantics beyond the schema. 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?

The description clearly states the verb ('Convert'), resource ('location string'), and output ('geographic coordinates'). It also mentions the specific service (OpenStreetMap geocoding) and distinguishes from the sibling tool 'astrology_calculate_natal_chart' by describing the prerequisite use case.

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 description explains when to use this tool ('before calculating a natal chart when only the city name is known'), which provides clear context. However, it does not explicitly state when not to use it or mention alternatives, though the sibling tool is the only alternative.

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

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. 2 tool updatesv1.0.8
    • First observedastrology_calculate_natal_chart
    • First observedastrology_get_coordinates
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TDQS

A4.1/5.0
Disambiguation5/5

Each tool has a clearly distinct purpose: one calculates a natal chart, the other converts a location to coordinates for input; no ambiguity.

Naming Consistency5/5

Both tools follow the 'astrology_verb_noun' pattern consistently, making the naming predictable and clear.

Tool Count3/5

Two tools is minimal for the domain of astrology; while the server may be scoped narrowly, a typical user might expect additional tools like transit or synastry calculations, making it borderline.

Completeness4/5

The server covers the essential steps for natal chart calculation (coordinates + chart), but lacks tools for interpretation, aspects analysis, or other astrological functions, leaving minor gaps.

Maintenance

ActivityInactive
ResponsivenessNo issues

Resources

Unclaimed servers have limited discoverability.

Looking for Admin?

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