Click on "Install Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type @ followed by the MCP server name and your instructions, e.g., "@Swiss Ephemeris MCP Server calculate my birth chart for April 12, 1985 at 11:20 PM in New York City"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
A Model Context Protocol (MCP) server that provides astronomical calculations using the Swiss Ephemeris library. Calculate planetary positions, houses, chart points, and asteroids for any date and location.
Planetary Positions: Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto
Lunar Nodes: True and Mean Node calculations
Asteroids: Chiron, Ceres, Pallas, Juno, Vesta, Lilith
Houses: 12-house system using Placidus
Chart Points: Ascendant, Midheaven, IC, Descendant
Additional Points: South Node, Part of Fortune
Related MCP server: Astrology MCP Server
For local use with Claude Desktop, you need to install the Swiss Ephemeris swetest command:
# Install swetest (required for Claude Desktop usage)
git clone https://github.com/aloistr/swisseph.git /tmp/swisseph && \
cd /tmp/swisseph && \
make && \
cp swetest /usr/local/bin/ && \
rm -rf /tmp/swissephAdd to your Claude Desktop configuration:
{
"mcpServers": {
"swissEphemeris": {
"command": "npx",
"args": ["github:dm0lz/swiss-ephemeris-mcp-server"]
}
}
}git clone https://github.com/dm0lz/swiss-ephemeris-mcp-server.git
cd swiss-ephemeris-mcp-server
npm install
npm startThe server provides four main tools:
calculate_planetary_positionsCalculate astronomical data for a specific date, time, and location.
Parameters:
datetime (string): ISO8601 format, e.g., "1985-04-12T23:20:50Z"
latitude (number): Latitude in decimal degrees (-90 to 90)
longitude (number): Longitude in decimal degrees (-180 to 180)
Returns:
planets: Positions of all planets and celestial bodies
houses: 12 astrological houses
chart_points: Ascendant, Midheaven, IC, Descendant
additional_points: South Node, Part of Fortune
calculate_transitsCalculate birth chart positions and current transits for comparison.
Parameters:
birth_datetime (string): Birth datetime in ISO8601 format
latitude (number): Birth latitude in decimal degrees
longitude (number): Birth longitude in decimal degrees
Returns:
natal_chart: Complete birth chart data
current_transits: Current planetary positions
calculation_time: Timestamp of transit calculation
calculate_solar_revolutionCalculate solar return chart for a specific year (when Sun returns to natal position).
Parameters:
birth_datetime (string): Birth datetime in ISO8601 format
birth_latitude (number): Birth latitude in decimal degrees
birth_longitude (number): Birth longitude in decimal degrees
return_year (number): Year for solar return calculation (e.g., 2024)
return_latitude (number, optional): Solar return location latitude
return_longitude (number, optional): Solar return location longitude
Returns:
natal_chart: Original birth chart data
solar_return_chart: Solar return chart for the specified year
natal_sun_longitude: Original Sun position in degrees
return_sun_longitude: Solar return Sun position in degrees
calculation_time: Timestamp of calculation
calculate_synastryCalculate synastry chart between two people for relationship compatibility analysis.
Parameters:
person1_datetime (string): Person 1 birth datetime in ISO8601 format
person1_latitude (number): Person 1 birth latitude in decimal degrees
person1_longitude (number): Person 1 birth longitude in decimal degrees
person2_datetime (string): Person 2 birth datetime in ISO8601 format
person2_latitude (number): Person 2 birth latitude in decimal degrees
person2_longitude (number): Person 2 birth longitude in decimal degrees
Returns:
person1_chart: Complete birth chart for person 1
person2_chart: Complete birth chart for person 2
synastry_aspects: Array of planetary aspects between the charts
calculation_time: Timestamp of calculation
# Build and run
docker build -t swiss-ephemeris-mcp .
docker run -p 8000:8000 -e MCP_HTTP_MODE=true swiss-ephemeris-mcp
# Health check
curl http://localhost:8000/healthStdio: Default mode for Claude Desktop integration
HTTP: Use MCP_HTTP_MODE=true for web integration via ngrok
MCP URL: https://www.theme-astral.me/mcp
Repository: https://github.com/dm0lz/swiss-ephemeris-mcp-server
Swiss Ephemeris: https://www.astro.com/swisseph/
MIT
Calculate planetary positions, houses, chart points and asteroids for a given datetime and coordinates
| Name | Required | Description | Default |
|---|---|---|---|
| datetime | Yes | ISO8601 datetime, e.g., 1985-04-12T23:20:50Z | |
| latitude | Yes | Latitude in decimal degrees | |
| longitude | Yes | Longitude in decimal degrees, positive east |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden of behavioral disclosure. It only states the purpose and inputs, omitting any behavioral traits such as computational complexity, permission requirements, error handling for invalid coordinates, or the nature of the output (e.g., read-only calculation).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single sentence of 15 words, front-loaded with the action 'Calculate'. It is efficient but could be restructured to include more critical information without increasing length.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
The tool has no output schema and moderate complexity. The description lists what is calculated but does not clarify the return format, data structure, or assumptions (e.g., geocentric vs heliocentric). Error handling and edge cases are not mentioned.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100% for all three parameters, so the baseline is 3. The description adds context about what is calculated (planetary positions, houses, chart points, asteroids) but does not enhance meaning beyond the schema's property descriptions.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'Calculate' and the resource 'planetary positions, houses, chart points and asteroids', specifying the inputs (datetime and coordinates). It effectively distinguishes this tool from siblings (calculate_solar_revolution, calculate_synastry, calculate_transits) which handle different astrological aspects.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage for calculating astrological positions but does not explicitly state when to use this tool versus alternatives. No when-not or exclusionary language is provided, leaving the agent to infer context from sibling tool names.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Calculate solar return chart for a specific year. The solar return occurs when the Sun returns to the exact same position as at birth.
| Name | Required | Description | Default |
|---|---|---|---|
| birth_datetime | Yes | Birth datetime in ISO8601 format, e.g., 1985-04-12T23:20:50Z | |
| birth_latitude | Yes | Birth latitude in decimal degrees | |
| birth_longitude | Yes | Birth longitude in decimal degrees, positive east | |
| return_year | Yes | Year for the solar return calculation, e.g., 2024 | |
| return_latitude | No | Latitude for solar return location (optional, defaults to birth location) | |
| return_longitude | No | Longitude for solar return location (optional, defaults to birth location) |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Given no annotations, the description should disclose behavioral traits like permissions, side effects, or output nature. It only explains the concept of a solar return, not whether it's read-only, what data it accesses, or what the output contains (no output schema).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences front-load the purpose and provide a concise astronomical definition. No redundant information; every word contributes to understanding the tool's core function.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
With 6 parameters and no output schema, the description lacks completeness. It doesn't explain the output format, how the chart differs from transits, or what the optional location parameters imply (e.g., relocation chart). It's insufficient for a complex astrological tool.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the description doesn't need to add parameter details. It provides context about the solar return but no additional meaning for individual parameters, maintaining the baseline of 3.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description explicitly states it calculates a solar return chart and defines the astronomical event (Sun returning to birth position). This clearly distinguishes it from sibling tools like planetary positions, synastry, or transits.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No guidance on when to use this tool versus alternatives (e.g., transits or synastry). It only states the tool's function without contextualizing its use relative to siblings or providing prerequisites.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Calculate synastry chart between two people for relationship compatibility analysis. Compares planetary positions and calculates aspects between the charts.
| Name | Required | Description | Default |
|---|---|---|---|
| person1_datetime | Yes | Person 1 birth datetime in ISO8601 format, e.g., 1985-04-12T23:20:50Z | |
| person1_latitude | Yes | Person 1 birth latitude in decimal degrees | |
| person1_longitude | Yes | Person 1 birth longitude in decimal degrees, positive east | |
| person2_datetime | Yes | Person 2 birth datetime in ISO8601 format, e.g., 1990-08-25T14:30:00Z | |
| person2_latitude | Yes | Person 2 birth latitude in decimal degrees | |
| person2_longitude | Yes | Person 2 birth longitude in decimal degrees, positive east |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Discloses that it compares positions and calculates aspects, but lacks details on output format, calculation methodology, or any side effects. With no annotations, the description carries the burden but is insufficiently detailed.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two concise sentences with no fluff. Every word adds value: clear verb, resource, and what the calculation entails. Well-structured.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
No output schema is provided, yet the description does not detail the return values. For a tool with 6 required parameters and no annotations, the description is insufficiently complete; it should hint at the output structure or any important behavioral details.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% with descriptions for all 6 parameters. The description adds no additional meaning beyond what the schema already provides, so baseline score of 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
Description clearly states the verb 'calculate' and resource 'synastry chart', and explains it compares planetary positions and aspects for relationship compatibility. It uniquely distinguishes from sibling tools like calculate_planetary_positions (single person).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Implies usage for relationship compatibility but does not explicitly state when to use this tool versus alternatives like calculate_transits or calculate_solar_revolution. No exclusions or prerequisites are mentioned.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Calculate birth chart positions and current transits for comparison. Returns both natal chart and current planetary positions.
| Name | Required | Description | Default |
|---|---|---|---|
| birth_datetime | Yes | Birth datetime in ISO8601 format, e.g., 1985-04-12T23:20:50Z | |
| latitude | Yes | Birth latitude in decimal degrees | |
| longitude | Yes | Birth longitude in decimal degrees, positive east |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries full burden. It states the tool calculates and returns positions, but gives no insight into behavior such as required authentication, rate limits, error handling for invalid coordinates, or the format of the return data.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two concise sentences with no wasted words. The key information is front-loaded: purpose and return value are immediately clear.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Despite no output schema, the description adequately explains that both natal and current planetary positions are returned. For a tool with 3 parameters and moderate complexity, this is nearly complete; however, it could benefit from mentioning the scope of planets or aspects included.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%: birth_datetime, latitude, and longitude are all clearly described in the schema. The tool description adds no additional parameter context beyond what is already provided by the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
Description clearly states the tool calculates birth chart positions and current transits for comparison, and returns both natal chart and current planetary positions. This distinguishes it from siblings like calculate_planetary_positions (likely just positions) and calculate_synastry (comparison between two people).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage when comparing natal and transit positions, but does not explicitly state when to use this tool versus alternatives like calculate_planetary_positions or calculate_solar_revolution. No exclusions or prerequisites are mentioned.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
v1.0.2calculate_planetary_positionscalculate_solar_revolutioncalculate_synastrycalculate_transitsScored across 4 tools
Each tool targets a distinct astrological calculation (general positions, solar return, synastry, transits), but calculate_planetary_positions and calculate_transits both involve planetary positions, potentially causing confusion. Descriptions help differentiate.
All tools use a consistent 'calculate_' verb followed by a snake_case noun phrase, forming a clear and predictable pattern.
With 4 tools, the set is well-scoped for an ephemeris server, covering essential calculations without being overly sparse or bloated.
The tools cover key astrological functions (positions, transits, synastry, solar return), but missing some operations like progressions or aspect-only calculations, though these may be included in outputs.
Unclaimed servers have limited discoverability.
If you are the server author, to access and configure the admin panel.
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