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. 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
- 120
- 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
Ask Claude about tonight's sky, someone's chart, or the next eclipse — and it quietly reaches for the real numbers instead of making them up. 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 OpenEphemeris
“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 OpenEphemeris 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.
Pricing
Transparent compute. Predictable bills.
Every tier includes core JSON math and LLM format. Higher tiers unlock progressively more powerful features — transit search, predictive math, astrocartography, and high-volume production queues. Overages are strict opt-in with a hard spend cap.
Pro
Unlock full math
Billed $264/yr
75,000
credits / month
+ overage: $2.50 / 10,000 credits (coming soon)
- 75,000 credits/month
- Production-scale commercial volume
- Full predictive math (returns, progressions)
- Comparative math (synastry, composite)
- Astrocartography standard (power lines, CCG)
- Electional astrology endpoints
- Comparative visualization (bi-wheel SVG)
Startup
Visual infrastructure unlocked
Billed $720/yr
500,000
credits / month
+ overage: $2.00 / 10,000 credits (coming soon)
- 500,000 credits/month
- Batch natal chart computation
- Priority support
Scale
High-volume production
Billed $1800/yr
2,000,000
credits / month
+ overage: $1.50 / 10,000 credits (coming soon)
- 2,000,000 credits/month
- Advanced ACG (aspects, midpoints, hermetic)
- Priority rate-limiting queues
- Dedicated support channel
99.9% uptime target · live status · fully licensed — zero AGPL exposure, no per-chart license fees
How credits work
Natal charts cost 1 credit · synastry 3 · astrocartography 10. MCP and API calls share one balance. Overage is strict opt-in with a hard spend cap.
+
How credits work
Natal charts cost 1 credit · synastry 3 · astrocartography 10. MCP and API calls share one balance. Overage is strict opt-in with a hard spend cap.
Standard Math
Natal charts, lunar phases, dignities, timezone, LLM JSON
Human Design
HD charts, composites, transits, penta, solar returns
Comparative Math
Synastry, composite, overlay charts
Visual Rendering
SVG chart wheels, PNG exports (Explorer+)
Predictive Math
Transit search (Explorer+), progressions, returns (Pro+)
Transit Chart
Transit chart snapshot (full chart at a single moment)
Astrocartography
Power lines, CCG, GeoJSON (Pro+), advanced ACG (Scale+)
ACG Hits
Location-specific planetary strength analysis
Calendar
Cross-quarter dates, lunar standstills, moon phases
Electional
Electional astrology search endpoints
Overage stays behind a hard wall.
Overage is strict opt-in only. You set an explicit spend cap before any extra credits are billed. When the cap is reached, requests stop instead of silently bleeding spend.
Overage billing is coming soon. Until it launches, requests beyond your monthly credits are declined — never billed. The rates shown per plan are the committed pricing for when it goes live.
FAQ
Common questions
How is this different from wrapping open-source ephemeris libraries myself?+
Three things. 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. OpenEphemeris 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 120 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?+
By default, overage is off and usage stops at your included credits. If you opt in, you must set a hard spend cap first. Once that cap is reached, overage stops automatically.
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 OpenEphemeris without writing any code?+
Yes. Connect via Claude Desktop or Claude Web with a single config paste or URL. Once connected, ask Claude to calculate a natal chart, find a transit, or read a Human Design profile in plain language. No terminal, no code editor needed.