Astrology, calculated —
powering your AI astrology agents.
Live sky · seeded from today's real positions
Sub-arcsecond planetary positions, aspects, and full chart structures — served through one clean REST API, or straight inside Claude and ChatGPT. Real astronomy, never guessed.
150 free trial credits · no card required
For developers · REST API
Build with the API
Natal charts, transits, synastry, astrocartography, Human Design, BaZi — clean JSON in, exact positions out. Typed errors, OpenAPI spec, one key for everything.
SVG straight from POST /ephemeris/natal-chart
- REST endpoints
- 121
- REST endpoints
- precision (JPL DE440)
- Sub-arcsecond
- precision (JPL DE440)
- of coverage (1550–2650)
- 1,100 yrs
- of coverage (1550–2650)
For AI agents · MCP server
Use it in Claude or ChatGPT
Ask Claude or ChatGPT about tonight's sky, someone's chart, or the next eclipse — and the answer comes from NASA JPL DE440, not from a guess. No code, no terminal.
Charts, bodygraphs, and maps render inside the conversation — not as text.
- things it can look up
- 92
- things it can look up
- answers from real data
- No guessing
- answers from real data
- to connect it
- One click
- to connect it
Proof
Built on Open Ephemeris
“I built the astrology tool I always wanted, Chinese, Vedic and Western, with Claude over a couple of nights. Working like a charm.”
We run on it ourselves
ELA Map — our own locational astrology & Human Design platform — runs entirely on these endpoints. Every line, crossing, relocated chart, and bodygraph it renders comes from the same public API you'd be calling.
ELA MapBuilt and operated by the Open Ephemeris team
Token Efficiency · Benchmarked Jul 12, 2026
13–97% fewer tokens per response.
Measured against the live production API with real GPT-4o and Claude tokenizers. Weighted average 62% across 7 endpoints; click any row below to see your actual cost.
Supported endpoints (7)
click a row to compute cost
Cost at 10,000 calls/mo
Astrocartography hits · GPT-4o
You save
$149/mo
97.0% reduction · same data depth
Measured against api.openephemeris.com on Jul 12, 2026 · GPT-4o tokenizer: o200k_base · Claude tokens via claude-sonnet-4-5 count_tokens API · Range: 12.7%–97.0% per endpoint
Stops spatial hallucinations
Models reason over pre-computed orbs and dignities instead of inventing them. The math arrives solved.
No system prompt needed
Our compact output shape is self-describing. Your agent parses it directly — no 2,000-token preamble explaining what each field means.
One API.
Infinite things
to build with it.
Whatever you're making — if the sky is part of it, we handle the math. One key, one call, any tradition. Or skip the code entirely and drop a chart widget on your site.
Rendered by the API
5
Traditions
Western, Vedic, BaZi, Human Design, and Hellenistic technique — one key, one call, any of them.
7
House Systems
Placidus, Koch, Porphyry, Regiomontanus, Campanus, Equal, Whole Sign — switch geometric models natively.
90
Celestial Bodies
Planets, nodes, Lilith variants, centaurs, 57 asteroids, trans-Neptunians, and the Uranian hypotheticals — plus 124 fixed stars.
1,100 yrs
of Coverage
1550–2650 CE on NASA JPL DE440 for the Sun, Moon, and core asteroid kernel — with dignities, cazimi, sect, out-of-bounds, and all seven Hermetic Lots throughout. The extended trans-Neptunian, centaur, and asteroid catalog carries full kernel precision for 1600–2200 CE.
FAQ
Common questions
Is this a Swiss Ephemeris API? How is it different from wrapping open-source ephemeris libraries myself?+
No. Open Ephemeris is not Swiss Ephemeris behind an API; it is a separate engine, and a hosted alternative to Swiss Ephemeris. Three things set it apart. First, First, we compute against NASA JPL DE440—sub-arcsecond precision across 1,100 years—directly. Second, you skip the AGPL trap: Swiss Ephemeris ships under AGPL, a viral license that requires you to publish your entire codebase if your hosted app links against it, or pay Astrodienst a commercial license fee. Open Ephemeris is a fully-licensed REST API, so your proprietary codebase stays clean with zero AGPL exposure and no Astrodienst negotiation. Third, we serve pre-computed aspects, dignities, orbs, and 121 higher-level endpoints (astrocartography, Human Design, electional) so your code never touches trig.
Full feature-by-feature comparison on the Swiss Ephemeris comparison page.
Why does format=llm matter for AI agents?+
It returns the same data in a token-compressed shape an LLM can parse directly. Measured against production with real tokenizers: 13–97% fewer tokens per response across supported endpoints (synastry, natal-transits, Human Design, ACG hits), weighted average 62%. The live benchmark with cost calculator is on this page. Your inference bill drops, and your model stops hallucinating planetary positions because the math arrives solved.
What happens if I exceed my credit limit?+
Requests beyond your monthly credits are declined, never billed. If you hold top-up credits they're used next, and subscribers buy top-ups at half price on the wallet page. Turn on auto top-up to refill automatically when your balance drops below a mark you set, up to a monthly limit you set. Overage billing is coming soon.
Is there a free ephemeris API?+
Yes. The Explorer tier is a genuinely free ephemeris API—150 credits on signup, no credit card, no daily cap. That covers planetary positions, natal charts, transit search, Human Design, and chart rendering against the same NASA JPL DE440 data every paid tier uses. Credits never expire, so there is no clock running while you build.
Full endpoint and tier breakdown on the astrology API page.
Can I use Open Ephemeris without writing any code?+
Yes. Install it from the ChatGPT app directory in one click, or add it to Claude as a connector. Once connected, ask for a natal chart, a transit, or a Human Design profile in plain language — and the chart renders right in the conversation. No terminal, no code editor needed.