# @getbirthchart/mcp

Official MCP server `0.2.0` for GetBirthChart astrology calculations. It gives
MCP-compatible AI clients access to structured calculations through the public
GetBirthChart API; it does not contain or reimplement the astrology engine.

## Requirements

- Node.js 20 or newer
- A GetBirthChart developer API key

Create a key at [getbirthchart.com/developers](https://getbirthchart.com/developers). Keep it private and do not commit MCP host configuration containing the real key.

## Quick start

The package runs over MCP stdio and can be launched with `npx`:

```json
{
  "mcpServers": {
    "getbirthchart": {
      "command": "npx",
      "args": ["-y", "@getbirthchart/mcp@0.2.0"],
      "env": {
        "GETBIRTHCHART_API_KEY": "gbc_live_your_key_here"
      }
    }
  }
}
```

This is the standard command-based configuration for hosts that support MCP stdio servers. Use your client’s current documentation for the exact configuration file or UI location; this repository has been protocol-tested with the official MCP TypeScript client, not vendor-specific clients.

## Environment variables

| Variable                     | Required | Description                                                                               |
| ---------------------------- | -------- | ----------------------------------------------------------------------------------------- |
| `GETBIRTHCHART_API_KEY`      | Yes      | Server-side developer API key.                                                            |
| `GETBIRTHCHART_API_BASE_URL` | No       | HTTPS API base URL override for development/testing. HTTP is accepted only for localhost. |

The key is read at startup, never accepted as a tool argument, and never written to stdout, logs, resources, or tool results.

## Available tools

All tools are read-only and return structured calculation facts. Inputs use strict fields: `date`, optional `time` and `place`, required `latitude`, `longitude`, and `timezone`, plus optional `unknown_time` and calculation settings documented below.

| Tool                    | Input                                      | Output                         | Exact time required? | Unknown-time behavior                                         |
| ----------------------- | ------------------------------------------ | ------------------------------ | -------------------- | ------------------------------------------------------------- |
| `calculate_birth_chart` | `birthData`                                | Mapped natal chart              | No                   | Omits Ascendant and houses; preserves uncertainty.            |
| `get_planet_positions`  | `birthData`                                | Planet placements               | No                   | Preserves chart uncertainty.                                  |
| `get_big_three`         | `birthData`                                | Sun, Moon, and optional Rising  | No                   | Does not guess the Ascendant.                                 |
| `get_moon_sign`         | `birthData`                                | Moon sign and uncertainty       | No                   | Returns ambiguity when the backend cannot establish one sign. |
| `get_rising_sign`       | `birthData`                                | Rising sign                     | Yes                  | Returns `birth_time_required`.                                |
| `calculate_aspects`     | `birthData`                                | Natal aspects                   | No                   | Returns backend-owned facts only.                             |
| `calculate_synastry`    | `person_a`, `person_b`, relationship fields | Synastry aspects and summaries | Per person           | Preserves each person's unknown-time limits.                  |

The current public API does not geocode `place`; provide latitude, longitude,
and an IANA timezone even when a place label is included. The MCP server never
invents a birth time. The backend may use local midnight as the labeled
calculation anchor for an unknown-time assessment, but it never presents that
anchor as the person's birth time and never guesses houses, the Ascendant, or
an ambiguous Moon sign.

Example input:

```json
{
  "date": "1990-01-15",
  "time": "12:00",
  "place": "New York, NY",
  "latitude": 40.7128,
  "longitude": -74.006,
  "timezone": "America/New_York"
}
```

Unknown time:

```json
{
  "date": "1990-01-15",
  "unknown_time": true,
  "latitude": 40.7128,
  "longitude": -74.006,
  "timezone": "America/New_York"
}
```

## Calculation options

The natal tools accept the exposed core `gbc-astro 1.13.0` options `house_system`,
`node_type`, `aspect_preset`, `custom_aspect_rules`, `additional_points`,
`fold`, `zodiac`, and `ayanamsa`. Omit them for the legacy-compatible defaults:
Tropical, Placidus, True Node, Standard aspects, Chiron on, and Lilith off.
Sidereal calculations require a named `ayanamsa`; Lahiri is the recommended
product choice. Custom aspects require `custom_aspect_rules` and each rule uses
`type`, `exact_angle`, and `orb`.

The implementation exposes the core's product-relevant house systems
(`placidus`, `whole_sign`, `equal`) plus the registered engine systems, Mean
Node, Standard/Extended/Custom natal aspects, Mean/True Lilith, Vertex and Part
of Fortune requests, and named sidereal ayanamsas. The MCP contract does not
add calculation logic or interpretation. Composite and Davison are core/SDK
operations but are not MCP tools in this release.

Synastry accepts a relationship-level `node_type` so both charts use one node
convention, plus optional `relationship_type`, `topic`, and `target_instant`.
The server preserves response metadata and additive schema 1.x fields. A natal
HTTP response may omit `calculationHash`; that is valid and is never required.
The server preserves a returned `v2:` calculation hash without changing or
truncating it. Core compatibility is natal schema `1.9.0` and synastry schema
`1.5.0`.

## Resources

- `getbirthchart://methodology` — calculation conventions and unknown-time boundaries.
- `getbirthchart://data-sources` — ephemeris, timezone, and location-input provenance.
- `getbirthchart://engine-info` — provider and public API metadata.

Authoritative web references: [Methodology](https://getbirthchart.com/methodology/) and [Data Sources](https://getbirthchart.com/data-sources/).

## Errors

Tool failures use structured `error` data with a safe machine-readable `code`, message, `retryable`, and optional `retry_after`. Common codes include `validation_error`, `authentication_required`, `birth_time_required`, `location_not_found`, `ambiguous_location`, `rate_limit_exceeded`, `timeout`, and `internal_error`.

## Troubleshooting

- **Missing API key:** set `GETBIRTHCHART_API_KEY` in the MCP host's server
  environment; it is never a tool argument.
- **Authentication or rate-limit errors:** use the structured error `code` and
  `retry_after` when present. Do not put the key in a tool call or client log.
- **Unknown-time validation:** omit `time` when `unknown_time` is `true`; the
  server will not substitute noon or invent a Rising sign.
- **Location validation:** include numeric WGS84 `latitude`, `longitude`, and
  an IANA `timezone`; `place` is only a label and is not geocoded here.
- **Local development:** use `GETBIRTHCHART_API_BASE_URL` only with HTTPS, or
  HTTP on localhost. Never send a production key to an untrusted host.

## Privacy and security

Birth data is passed only to the configured public API for the requested calculation. This package does not persist, cache, or log birth inputs, and it has no analytics or telemetry. The optional base URL override changes the trust boundary; do not send a production key to an untrusted host.

Report security issues privately through the process in [SECURITY.md](./SECURITY.md). Do not include API keys in bug reports.

## Development

```bash
npm install
npm run lint
npm run typecheck
npm test
npm run build
```

Tests use mocked clients and do not call the production API. To run the built server locally, set `GETBIRTHCHART_API_KEY` and execute `node dist/cli.js`; normal protocol traffic stays on stdout, while startup failures are written to stderr.

## Links

- [Developer hub](https://getbirthchart.com/developers)
- [GitHub repository](https://github.com/getbirthchart-com/getbirthchart-mcp)
- [Core 1.13.0 GitHub release](https://github.com/getbirthchart-com/gbc-astro-engine/releases/tag/v1.13.0)
- [Core 1.13.0 on PyPI](https://pypi.org/project/gbc-astro/1.13.0/)
- [Core OpenAPI source](https://github.com/getbirthchart-com/gbc-astro-engine/blob/v1.13.0/src/gbc_astro/api/models.py)
- [Concept DOI](https://doi.org/10.5281/zenodo.22052875) · [Version DOI](https://doi.org/10.5281/zenodo.22206006)
- [npm package](https://www.npmjs.com/package/@getbirthchart/mcp)

## MCP Registry metadata

Registry metadata is prepared in [`server.json`](./server.json) with server name `io.github.getbirthchart-com/getbirthchart-mcp`. Publish the npm package first, then authenticate with the official `mcp-publisher` tool and publish the metadata. Registry submission is intentionally not part of the package build or CI workflow.