# Open Ephemeris MCP Server

[![npm version](https://img.shields.io/npm/v/@openephemeris/mcp-server)](https://www.npmjs.com/package/@openephemeris/mcp-server)
[![System Status](https://img.shields.io/badge/Status-Operational-brightgreen)](https://status.openephemeris.com/)
[![License: MIT](https://img.shields.io/badge/License-MIT-blue)](LICENSE)
[![Ephemeris: JPL DE440](https://img.shields.io/badge/Ephemeris-JPL%20DE440-6f42c1)](https://ssd.jpl.nasa.gov/planets/eph_export.html)

![Open Ephemeris in Claude — ask in plain language, get a real computed chart](https://raw.githubusercontent.com/openephemeris/openephemeris-MCP/main/assets/hero-demo.gif)

**Use it in Claude:** add `https://mcp.openephemeris.com/mcp` as a custom connector (leave the OAuth Client ID and Secret blank) or install the Open Ephemeris plugin from the Claude directory. Sign-in happens in the browser and creates a free account with 150 credits.

Model Context Protocol server for Open Ephemeris — typed astrology tools powered by the NASA JPL DE440 ephemeris. Zero hallucination on planetary positions, dates, and degrees. Covers 1,100 years of astronomical data.

![The catalog: 90 bodies and 124 fixed stars — asteroids, trans-Neptunians, Uranian points, computed in one engine](https://raw.githubusercontent.com/openephemeris/openephemeris-MCP/main/assets/catalog-90-bodies.png)

**Hosted endpoint:** `https://mcp.openephemeris.com/mcp` (Streamable HTTP, MCP 2025-11-25 spec)

## Quick Start

### Quick install

Claude Code, one command:

```bash
claude mcp add openephemeris -- npx -y @openephemeris/mcp-server
```

Any client that takes a hosted URL (Claude Web, ChatGPT, custom agents): use `https://mcp.openephemeris.com/mcp` and send your API key in the `X-API-Key` header. Other clients are below.

---

### Connect from code (Streamable HTTP)

```typescript
import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js"
import { Client } from "@modelcontextprotocol/sdk/client/index.js"

const transport = new StreamableHTTPClientTransport(
  new URL("https://mcp.openephemeris.com/mcp"),
  { requestInit: { headers: { "X-API-Key": "your-openephemeris-api-key" } } }
)

const client = new Client({ name: "my-app", version: "1.0.0" }, { capabilities: {} })
await client.connect(transport)
```

---

### One-click install (Cursor)

<!-- GENERATED:CURSOR_INSTALL:BEGIN -->
[![Install in Cursor](https://img.shields.io/badge/Install%20in-Cursor-1f6feb)](cursor://anysphere.cursor-deeplink/mcp/install?name=openephemeris&config=eyJjb21tYW5kIjoibnB4IiwiYXJncyI6WyIteSIsIkBvcGVuZXBoZW1lcmlzL21jcC1zZXJ2ZXIiXSwiZW52Ijp7Ik9QRU5FUEhFTUVSSVNfUFJPRklMRSI6ImRldiIsIk9QRU5FUEhFTUVSSVNfQkFDS0VORF9VUkwiOiJodHRwczovL2FwaS5vcGVuZXBoZW1lcmlzLmNvbSIsIk9QRU5FUEhFTUVSSVNfQVBJX0tFWSI6IllPVVJfQVBJX0tFWV9IRVJFIn19)

> Replace `YOUR_API_KEY_HERE` in Cursor MCP settings with your API key from https://openephemeris.com/dashboard.

Cursor deeplink payload:
```json
{
  "command": "npx",
  "args": [
    "-y",
    "@openephemeris/mcp-server"
  ],
  "env": {
    "OPENEPHEMERIS_PROFILE": "dev",
    "OPENEPHEMERIS_BACKEND_URL": "https://api.openephemeris.com",
    "OPENEPHEMERIS_API_KEY": "YOUR_API_KEY_HERE"
  }
}
```
<!-- GENERATED:CURSOR_INSTALL:END -->

### Manual install (stdio MCP clients)

```json
{
  "mcpServers": {
    "openephemeris": {
      "command": "npx",
      "args": ["-y", "@openephemeris/mcp-server"],
      "env": {
        "OPENEPHEMERIS_PROFILE": "dev",
        "OPENEPHEMERIS_BACKEND_URL": "https://api.openephemeris.com",
        "OPENEPHEMERIS_API_KEY": "YOUR_API_KEY_HERE"
      }
    }
  }
}
```

### Platform guide

> **Detailed setup walkthroughs** for each platform are in [SETUP.md](./SETUP.md).

| Client | Install mode | Config location |
|---|---|---|
| Claude Code | CLI | `claude mcp add openephemeris -- npx -y @openephemeris/mcp-server` |
| Cursor | One-click deeplink or manual | `~/.cursor/mcp.json` |
| Claude Desktop (macOS) | Manual | `~/Library/Application Support/Claude/claude_desktop_config.json` |
| Claude Desktop (Windows) | Manual | `%APPDATA%\Claude\claude_desktop_config.json` |
| Windsurf | Manual | `~/.codeium/windsurf/mcp_config.json` (or legacy `~/.codeium/mcp_config.json`) |
| ChatGPT | One-click | [Open Ephemeris in the ChatGPT app directory](https://chatgpt.com/plugins/plugin_asdk_app_6a9c2787bc48819197698e71b29ef7c2) |
| Claude Web / remote clients | Hosted URL | `https://mcp.openephemeris.com/mcp` |

### Client install walkthroughs

1. Cursor
   - Click the "Install in Cursor" button above, then replace `YOUR_API_KEY_HERE` in Cursor MCP settings.
   - If you prefer manual setup, paste the `mcpServers.openephemeris` block from "Manual install" into `~/.cursor/mcp.json`.
2. Claude Desktop (macOS/Windows)
   - Open the platform config file from the table above.
   - Add the same `mcpServers.openephemeris` block from "Manual install".
   - Restart Claude Desktop.
3. Windsurf
   - Open `~/.codeium/windsurf/mcp_config.json` (or the legacy `~/.codeium/mcp_config.json` path).
   - Add the `mcpServers.openephemeris` block from "Manual install".
   - Restart Windsurf.

### Remote-only clients (Claude Web, ChatGPT, etc.)

The server is hosted at `https://mcp.openephemeris.com/mcp` with full Streamable HTTP support (MCP 2025-11-25 spec). Remote-only clients can connect directly — no bridge/proxy required:

- **Claude Web**: Add `https://mcp.openephemeris.com/mcp` as a custom connector URL — leave OAuth Client ID and Secret **blank**. The server uses OAuth 2.1 + PKCE (Dynamic Client Registration), so Claude handles authentication via a browser popup automatically.
- **ChatGPT**: Open Ephemeris is an approved app in the ChatGPT app directory. Open
  [the listing](https://chatgpt.com/plugins/plugin_asdk_app_6a9c2787bc48819197698e71b29ef7c2), click **Install plugin**, approve the sign-in (that also creates your
  free Open Ephemeris account), then type `@Open Ephemeris` in any chat. Charts render inline,
  exactly as they do in Claude. Prefer to wire it yourself? **Settings → Plugins → Advanced →
  Developer mode → + Create app** accepts `https://mcp.openephemeris.com/mcp` with
  Authentication on **OAuth** — no client ID or secret to enter.
- **Legacy SSE**: retired in 3.20.0 — use Streamable HTTP at `/mcp`

### Auth and upgrade behavior in MCP clients

- Missing/invalid credentials (`401`): tool call fails with a message that points users to sign up/sign in at `https://openephemeris.com/login?signup=true&redirect=%2Fdashboard%3Ftab%3Daccount`, then create/manage keys in `https://openephemeris.com/dashboard?tab=account`.
- Tier-gated endpoint (`403`): tool call returns an upgrade-required message with `https://openephemeris.com/pay` and dashboard billing/key management link.
- Out of credits (`402`): tool call returns a one-tap top-up link (Explorer's 150 free credits are one-time and do not reset; plan allowances renew each billing period) plus the dashboard usage link. Failed calls (any `4xx`/`5xx`) are refunded.
- Burst/rate limit (`429`): tool call returns retry guidance and links to dashboard usage monitoring.

## What You Can Ask

```
"Calculate a natal chart for 1990-04-15 at 2:30 PM in Chicago."
"Find all Saturn transits to my natal Sun in the next 6 months."
"Get the current moon phase and void-of-course status."
"Find the next solar eclipse visible from Tokyo."
"Find the best time to sign a contract in March — electional window."
"Generate a Human Design chart for my birth data."
"What is my Vedic (sidereal) chart?"
"Calculate my Chinese BaZi (Four Pillars) chart."
"Show me my Astrocartography power lines — where is my Venus line on the map?"
"Find all ACG lines within 3° of Paris for my chart."
"Calculate a synastry chart between two people."
"Find the next Venus Star Point and my relationship to it."
"What are the active planetary stations in the next 3 months?"
"Calculate primary directions for the next 5 years."
"Find my Firdaria time lord period."
"What is the sidereal time and delta-T right now?"
```

## Interactive Charts

Nine of the tools don't answer with JSON. They open a chart in the conversation — a real one, drawn from the same calculation, that you can click around in.

This matters more than it sounds. A natal chart returned as JSON is a list of numbers you have to already understand to read. The same chart rendered as a wheel is something you can point at. Click a planet and you get that placement explained; click a house and you get what's in it. The chart stays on screen while you keep talking, and it doesn't cost another credit to keep looking at it.

These need a host that supports MCP Apps. **Claude and ChatGPT both do**, and they render
the same widget — there is no separate ChatGPT build. MCP Apps ([SEP-1865][sep1865]) was
co-authored by Anthropic and OpenAI and became the first official MCP extension in January
2026, so one `ui://` resource serves both. In ChatGPT, install it from
[the app directory](https://chatgpt.com/plugins/plugin_asdk_app_6a9c2787bc48819197698e71b29ef7c2); in Claude, add the connector (see [SETUP.md](SETUP.md)).

In a client without app support the same tools still work; you get the underlying data
instead of the picture, so nothing breaks, you just don't get the wheel.

[sep1865]: https://modelcontextprotocol.io/seps/1865-mcp-apps-interactive-user-interfaces-for-mcp

| Tool | What opens | What you can click | Credits |
|---|---|---|---|
| `explore_natal_chart` | Natal wheel — planets, houses, aspects, angles | Planets, houses, aspect lines; recalculate with new settings | 1 |
| `explore_bi_wheel` | Two charts on one wheel: transits, synastry, progressions | Either wheel's planets, houses, and the aspects between them | 2 (6 for solar/lunar return) |
| `explore_human_design` | Human Design bodygraph, with a mandala view toggle | Centers, gates, channels, planets, variables | 4 |
| `explore_human_design_transit` | Today's planets laid over a natal bodygraph | Transit-activated channels | 5 |
| `explore_human_design_connection` | Two bodygraphs combined, every shared channel classified | Connection channels by type | 5 |
| `explore_vedic_chart` | South Indian Rashi grid — sidereal placements and Lagna | Each rashi, for its placements and nakshatras | 3 |
| `explore_bazi_chart` | Four Pillars (四柱命盘) — Year, Month, Day, Hour | Each pillar | 3 |
| `explore_transit_timeline` | Upcoming transit hits in date order | Individual hits | 6 for up to 1 year (priced by span) |
| `explore_moon_phase` | Moon dial — illumination, phase, sign, void-of-course | Recalculate for another moment | 3 |

Ask for these the way you'd ask a person: *"show me my chart"*, *"put today's transits over my Human Design"*, *"what's the moon doing right now"*. The model picks the app.

Two things worth knowing. The chart wheel and bi-wheel accept a click on an aspect line, not just on the two planets it joins — so "why does this line matter" is one click rather than a paragraph of setup. And the bodygraph's mandala toggle rearranges the whole chart into concentric rings without another API call, so switching views is free.

## Tools at a Glance

| Category | Tool | Tier |
|---|---|---|
| Natal chart | `ephemeris_natal_chart` | Explorer |
| Transit forecast | `ephemeris_transits` | Explorer |
| Transit chart snapshot | `ephemeris_natal_transits` | Explorer |
| Sign ingresses / planet to degree | `ephemeris_ingresses` | Explorer |
| Moon phase / VOC | `ephemeris_moon_phase` | Explorer |
| Eclipse next visible | `ephemeris_next_eclipse` | Explorer |
| Electional window | `ephemeris_electional` | Pro |
| Moment analysis | `electional_moment_analysis` | Explorer |
| Station tracker | `electional_station_tracker` | Explorer |
| Aspect search | `electional_aspect_search` | Pro |
| Human Design chart | `human_design_chart` | Explorer |
| HD composite | `human_design_composite` | Explorer |
| HD transit overlay | `explore_human_design_transit` | Explorer |
| HD transit timeline (gates over a date range) | `human_design_transit_timeline` | Explorer |
| HD extended placements (asteroids, angles, lots, stars) | `human_design_extended` | Explorer (deep fields Pro) |
| HD connection (synastry) | `explore_human_design_connection` | Explorer |
| HD penta | `human_design_penta` | Explorer |
| HD return / opposition | `hd_planetary_return`, `hd_opposition` | Explorer |
| Vedic chart | `vedic_chart` | Explorer |
| BaZi (Chinese) | `chinese_bazi` | Explorer |
| Synastry | `ephemeris_synastry` | Explorer |
| Composite chart | `ephemeris_composite` | Explorer |
| Relocation chart | `ephemeris_relocation` | Explorer |
| Progressed chart | `ephemeris_progressed_chart` | Explorer |
| Solar return | `ephemeris_solar_return` | Explorer |
| Lunar return | `ephemeris_lunar_return` | Explorer |
| Planetary return | `ephemeris_planetary_return` | Explorer |
| Astrocartography lines | `acg_power_lines` | Pro |
| ACG hits at location | `acg_hits` | Pro |
| Venus Star Points | `venus_star_points` + 4 more | Explorer |
| Chart wheel image | `ephemeris_chart_wheel` | Explorer |
| Bi-wheel image | `ephemeris_bi_wheel` | Explorer |
| Dignities / Midpoints / Fixed stars | `ephemeris_dignities`, `ephemeris_midpoints`, `ephemeris_fixed_stars` | Explorer |

## Tooling Model

- Typed tools are preferred for common workflows (natal, transits, moon phase, eclipse, synastry, relocation, electional, Human Design).
- Generic tools: `find_calculation` searches the allowlisted operations by plain words and returns the path, inputs, an example and the credit cost (`dev_list_allowed` lists them all, outside core); `dev_read_api` invokes allowlisted **GET** (read) operations and `dev_write_api` invokes allowlisted **POST/PUT/PATCH/DELETE** (write/compute) operations, each by `method + path`. Read and write are kept as separate tools so a safe read surface never shares a tool with state-changing writes.
- Security model: default-deny with explicit allowlist in `config/dev-allowlist.json`.
- Deny prefixes block sensitive route families (`/auth`, `/billing`, `/admin`, etc.).

### `dev_read_api` / `dev_write_api` input

| Parameter | Type | Required | Description |
|---|---|---|---|
| `method` | `dev_read_api`: `GET` · `dev_write_api`: `POST\|PUT\|PATCH\|DELETE` | No | HTTP method (defaults to the tool's natural method) |
| `path` | `string` | Yes | Absolute API path, e.g. `/ephemeris/natal-chart` |
| `query` | `object` | No | Query parameters |
| `body` | `object` | No | JSON body for non-GET requests |
| `preset` | `full\|simple` | No | Convenience mapping to `query.preset` |
| `format` | `json\|llm\|llm_v2` | No | Convenience mapping to `query.format` (`llm_v2` normalizes to `llm`) |
| `output_mode` | `full\|simple\|llm\|llm_v2` | No | Legacy compatibility field |

## Environment Variables

| Variable | Required | Description |
|---|---|---|
| `OPENEPHEMERIS_API_KEY` | Yes (unless service key/JWT used) | API key for Open Ephemeris |
| `ASTROMCP_API_KEY` | No | Legacy alias for `OPENEPHEMERIS_API_KEY` (checked as fallback) |
| `OPENEPHEMERIS_BACKEND_URL` | No | Defaults to `https://api.openephemeris.com` |
| `OPENEPHEMERIS_PROFILE` | No | `dev` by default |
| `OPENEPHEMERIS_TOOLS` | No | `core` (default) advertises a focused everyday tool set; `full` advertises every tool. See [Tool surface](#tool-surface) |
| `OPENEPHEMERIS_TELEMETRY` | No | Set to `0`/`false`/`off` to disable anonymous usage reporting. `DO_NOT_TRACK=1` also works. See [Telemetry](#telemetry) |
| `OPENEPHEMERIS_JWT` | No | Bearer token auth |
| `OPENEPHEMERIS_DEV_ALLOWLIST_PATH` | No | Override allowlist file path |
| `MCP_USER_ID` | No | Per-instance user identifier |

Legacy aliases (`ASTROMCP_*`, `MERIDIAN_*`) remain supported.

## Telemetry

This server reports anonymous usage so we know which tools are worth maintaining and which are broken. Three events: session start, tool call, tool error.

**What is sent:** the tool name, how long it took, error status, which MCP client connected (e.g. Claude Desktop, Cursor) and its version, the server version, and a stable id for the session: a one-way SHA-256 prefix of your API key, or your account ID when you sign in with OAuth.

**What is never sent:** your API key or token, birth data, dates, names, coordinates, tool arguments, or tool results. No request or response bodies, ever.

**To turn it off** — either works, checked before anything is sent:

```bash
OPENEPHEMERIS_TELEMETRY=0
# or the cross-tool standard
DO_NOT_TRACK=1
```

## Tool surface

By default the server advertises a **focused core set** of everyday tools rather than the entire catalog. Large tool lists cost context and make model tool-selection worse, so the default is tuned for real conversations: one interactive app per tradition, the primary data tool per domain, geocoding, and the allowlist-gated generic proxy.

**Nothing is removed.** The surface is a filter on `tools/list` only — every tool stays registered and stays callable by name. If you know the tool you want, call it and it works, listed or not.

To advertise the full catalog:

```bash
OPENEPHEMERIS_TOOLS=full npx -y @openephemeris/mcp-server
```

On the remote HTTP server, append `?profile=full` to the connector URL (or send `X-OE-Tool-Surface: full`):

```
https://mcp.openephemeris.com/mcp?profile=full
```

### Toolsets by tradition

If you work in one tradition, ask for it by name instead of taking the general-purpose default. You get that tradition in full — including the long-tail tools the core set leaves out — for a fraction of the context.

```bash
OPENEPHEMERIS_TOOLS=hd npx -y @openephemeris/mcp-server        # Human Design
OPENEPHEMERIS_TOOLS=astrology,moon npx -y @openephemeris/mcp-server
```

```
https://mcp.openephemeris.com/mcp?profile=hd,bazi
```

| Toolset | What it covers | Tools | Approx. tokens |
|---|---|---:|---:|
| `astrology` | Natal, transits, ingresses, synastry, progressions, returns, relocation, time lords, dignities, midpoints, lots, fixed stars, composites, birth-time sensitivity | 38 | 17,700 |
| `hd` | Human Design charts, transits and transit timeline, extended placements, connection charts, penta, bodygraph | 19 | 8,500 |
| `bazi` | Four Pillars, Ten Gods, element balance, luck pillars, compatibility, Zi Wei Dou Shu | 16 | 8,100 |
| `electional` | Timing windows, angle crossings, stations, moment analysis | 12 | 4,300 |
| `acg` | Astrocartography lines and hits | 9 | 3,400 |
| `vedic` | Jyotish Rashi chart, dashas, vargas, Ashtakoota matching | 10 | 3,400 |
| `moon` | Phases, void-of-course, eclipses | 11 | 3,300 |
| `venus` | Star points, phases, elongations, stations | 13 | 3,200 |
| `mundane` | Ingress and lunation charts, geodetic chart | 9 | 2,600 |
| — | *core (default)* | 39 | 19,800 |
| — | *full* | 81 | 39,100 |

Every selection also includes geocoding (`location_search`, `timezone_resolve`), `account_usage`, and the allowlist-gated proxy — so a birthplace is always resolvable and nothing is stranded.

Combine with commas; unknown names are ignored rather than rejected, so a typo degrades to a smaller surface instead of a dead connector. As with `core`/`full`, this only filters `tools/list` — every tool remains callable by name.

Why it matters: tool definitions are re-sent to the model on **every** pass. `astrology,moon` advertises a few more tools than the default but costs ~700 fewer tokens per message and covers more of the tradition.

The surface is fixed when the session initializes — this server does not advertise `tools.listChanged`, so switching requires reconnecting. On every surface, `find_calculation` searches every operation reachable through the generic proxy.

## Contributing & Support

- **Something wrong with a result?** [Open an issue](https://github.com/openephemeris/openephemeris-MCP/issues/new/choose) — include the tool, your inputs, and what you expected.
- **Want to contribute?** See [CONTRIBUTING.md](CONTRIBUTING.md). Integration examples and new skills are the most useful things you can add.
- **Found a security problem?** Please report it privately — see [SECURITY.md](SECURITY.md).
- **Tools timing out?** Check [status.openephemeris.com](https://status.openephemeris.com) first.

If this saved you from an LLM confidently inventing a Saturn position, a ⭐ helps other people find it.

## Legal

This package is licensed under the [MIT License](./LICENSE). However, use of this package to access the Open Ephemeris API constitutes use of the Service and is governed by the [Open Ephemeris Terms of Service](https://openephemeris.com/terms). By using this package, you agree to those terms. See also the [Privacy Policy](https://openephemeris.com/privacy) and [Acceptable Use Policy](https://openephemeris.com/acceptable-use).

## Development

The server source is maintained in a private monorepo; this repository holds the public docs, plugin, skills and examples. Bug reports and contributions are welcome — see [CONTRIBUTING.md](CONTRIBUTING.md).

## Architecture

```text
┌─────────────────────────────────────────────────────────┐
│                    MCP Clients                          │
│  Codex · Gemini   · Claude Web · ChatGPT · Remote apps  │
└──────────────────┬──────────────────────────────────────┘
                   │ Streamable HTTP (MCP 2025-11-25)
                   │ https://mcp.openephemeris.com/mcp
                   │
┌─────────────────────────────────────────────────────────┐
│          Cursor · Claude Desktop · Windsurf             │
└──────────────────┬──────────────────────────────────────┘
                   │ stdio JSON-RPC
                   │ npx @openephemeris/mcp-server
                   │
              ┌────▼────────────────────┐
              │  openephemeris-mcp      │
              │  Node.js MCP Server     │
              │  typed tools            │
              │  auth: Key > JWT        │
              └────────────┬────────────┘
                           │ HTTPS
                           ▼
              ┌────────────────────────┐
              │  Open Ephemeris API    │
              │  api.openephemeris.com │
              │  NASA JPL DE440        │
              │  1,100 years of data   │
              └────────────────────────┘
```

<!-- GENERATED:RUNTIME_SNAPSHOT:BEGIN -->
## Runtime Snapshot (Generated)

Generated by `npm run sync:readme` from `config/dev-allowlist.json` and the live tool registry.

- Allowlisted operations: **140**
- Methods: `GET=45`, `POST=95`, `PUT=0`, `PATCH=0`, `DELETE=0`
- Registered tools (`OPENEPHEMERIS_PROFILE=dev`): **103**
- Typed tools: `account_usage`, `acg_hits`, `acg_power_lines`, `auth_login`, `auth_logout`, `auth_status`, `bazi_annual_pillar`, `bazi_chart`, `bazi_compatibility`, `bazi_element_balance`, `bazi_luck_pillars`, `bazi_recalculate`, `bazi_ten_gods`, `bi_wheel_on_cross_aspect_click`, `bi_wheel_on_house_click`, `bi_wheel_on_planet_click`, `bi_wheel_recalculate`, `bi_wheel_synopsis`, `bodygraph_recalculate`, `chart_wheel_on_aspect_click`, `chart_wheel_on_house_click`, `chart_wheel_on_planet_click`, `chart_wheel_recalculate`, `chinese_bazi`, `electional_angle_crossings`, `electional_aspect_search`, `electional_moment_analysis`, `electional_station_tracker`, `ephemeris_angles_points`, `ephemeris_aspect_check`, `ephemeris_bi_wheel`, `ephemeris_chart_wheel`, `ephemeris_composite`, `ephemeris_composite_midpoint`, `ephemeris_dignities`, `ephemeris_electional`, `ephemeris_fixed_stars`, `ephemeris_hermetic_lots`, `ephemeris_house_cusps`, `ephemeris_ingresses`, `ephemeris_lunar_return`, `ephemeris_midpoints`, `ephemeris_moon_phase`, `ephemeris_natal_batch`, `ephemeris_natal_chart`, `ephemeris_natal_transits`, `ephemeris_next_eclipse`, `ephemeris_next_lunar_phase`, `ephemeris_overlay`, `ephemeris_planet_position`, `ephemeris_planetary_return`, `ephemeris_progressed_chart`, `ephemeris_relocation`, `ephemeris_retrograde_status`, `ephemeris_solar_return`, `ephemeris_synastry`, `ephemeris_time_lords`, `ephemeris_time_sensitivity`, `ephemeris_transits`, `explore_bazi_chart`, `explore_bi_wheel`, `explore_human_design`, `explore_human_design_connection`, `explore_human_design_transit`, `explore_moon_phase`, `explore_natal_chart`, `explore_transit_timeline`, `explore_vedic_chart`, `geodetic_chart`, `hd_connection_matrix`, `hd_on_center_click`, `hd_on_channel_click`, `hd_on_connection_channel_click`, `hd_on_gate_click`, `hd_on_planet_click`, `hd_on_transit_channel_click`, `hd_on_variable_click`, `hd_opposition`, `hd_planetary_return`, `human_design_bodygraph`, `human_design_chart`, `human_design_composite`, `human_design_extended`, `human_design_penta`, `human_design_transit_timeline`, `location_search`, `moon_phase_recalculate`, `mundane_chart`, `timezone_resolve`, `vedic_chart`, `vedic_chart_recalculate`, `vedic_matching`, `venus_eight_year_star`, `venus_elongations`, `venus_phase`, `venus_star_points`, `venus_star_points_conjunctions`, `venus_stations`, `ziwei_chart`
- Generic tools: `dev_list_allowed`, `dev_read_api`, `dev_write_api`, `find_calculation`

### Allowlist Families

| Family | Operations | Example |
|---|---:|---|
| `acg` | 14 | `POST /acg/aspects`, `POST /acg/ccg` |
| `calendar` | 3 | `GET /calendar/astrology/cross-quarter`, `GET /calendar/astrology/lunar-standstill` |
| `catalogs` | 3 | `GET /catalogs/bodies`, `GET /catalogs/fixed-stars` |
| `chinese` | 12 | `POST /chinese/bazi`, `POST /chinese/bazi/annual-pillar` |
| `comparative` | 5 | `POST /comparative/composite`, `POST /comparative/composite/midpoint` |
| `eclipse` | 6 | `GET /eclipse/besselian-elements`, `GET /eclipse/lunar/global` |
| `electional` | 6 | `GET /electional/angle-crossings`, `GET /electional/aspect-search` |
| `ephemeris` | 42 | `GET /ephemeris/agro/calendar`, `GET /ephemeris/agro/daily` |
| `health` | 2 | `GET /health`, `GET /health/detailed` |
| `human-design` | 11 | `POST /human-design/chart`, `POST /human-design/composite` |
| `location` | 2 | `GET /location/autocomplete`, `GET /location/reverse` |
| `mundane` | 1 | `POST /mundane/chart` |
| `predictive` | 14 | `POST /predictive/eclipses/natal-hits`, `POST /predictive/primary-directions` |
| `root` | 1 | `GET /` |
| `tidal` | 1 | `GET /tidal/forcing` |
| `time` | 6 | `GET /time/delta-t`, `GET /time/equation-of-time` |
| `timezone` | 3 | `GET /timezone/coverage`, `POST /timezone/lookup` |
| `vedic` | 5 | `POST /vedic/chart`, `POST /vedic/kp` |
| `visualization` | 3 | `POST /visualization/bi-wheel`, `POST /visualization/bodygraph` |
<!-- GENERATED:RUNTIME_SNAPSHOT:END -->

## Why Open Ephemeris for AI Agents?

Most LLMs (like Claude and ChatGPT) struggle heavily with astronomical calculations (trigonometry, Julian date conversions, and planetary lookups). Open Ephemeris serves as a **secure, remote math engine**.

By pairing LLMs with the Open Ephemeris MCP server, your agents can instantly access:
- **Zero-hallucination coordinates**: Direct, sub-arcsecond NASA JPL DE440 calculations spanning 1,100 years of astronomical data.
- **LLM-optimized tokens (`format=llm`)**: We compress standard 25,000 token JSON chart responses into minimal text blocks, cutting your inference costs by 50–73% depending on endpoint.
- **Ready-to-use astrology layers**: Built-in support for Astrocartography geoJSON lines, Hermetic Lots, Fixed Stars, and complex Human Design matrix generation.