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 credits · no credit card
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.
- REST endpoints
- 118
- REST endpoints
- position error
- < 0.01″
- position error
- median latency
- ~85ms
- median latency
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.
- things it can look up
- 84
- 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.”
“ELA Map’s locational astrology and Human Design platform runs entirely on OpenEphemeris. The precision, the speed, the breadth of endpoints, and genuinely responsive support are what made a product this ambitious possible.”
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.
Live output
12
House Systems
Placidus, Whole Sign, Koch, Regiomontanus and more — switch geometric models natively.
70+
Celestial Bodies
Planets, true/mean nodes, Lilith variants, Trans-Neptunian objects, and dozens of asteroids.
110
Fixed Stars
Every major Ptolemaic star, tracked to sub-arcsecond accuracy across thousands of years.
∞
Interpretive Logic
Dignities, cazimi, combustion, sect, out-of-bounds, and all seven Hermetic Lots.
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
- Licensed for commercial use
- 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
What does OpenEphemeris actually do?+
It computes precise planetary positions, aspects, dignities, transits, and chart structures through a clean REST API—so you can build astrology apps, timing features, maps, and automations without building astronomy math in-house.
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 118 higher-level endpoints (astrocartography, Human Design, electional) so your code never touches trig.
Open Ephemeris Pro — $29/mo | Leading Credit API $19/mo | Leading REST API $11/mo | |
|---|---|---|---|
| Monthly price | $29 | $19 | $11 |
| Included credits / calls | 75,000 | 100,000* | 5,000 |
| Credits per standard chartⓘ | 1 | 500 | 1 |
| Actual charts includedⓘ | 75,000 | ~200 | 5,000 |
| True cost per chart | $0.0004 | $0.0950 | $0.0022 |
| Predictive charts includedⓘ | 15,000 | ~125 | 0 |
| Compute engine | JPL DE440 | Swiss Ephemeris | Static lookups |
| LLM-optimized output | ✓ format=llm | ✗ | ✗ |
| Overage policy | Opt-in, capped | Hard 429 crash | Hard 429 crash |
Monthly price
OE
$29
Credit API
$19
REST API
$11
Included credits / calls
OE
75,000
Credit API
100,000*
REST API
5,000
Credits per standard chart
OE
1
Credit API
500
REST API
1
Actual charts included
OE
75,000
Credit API
~200
REST API
5,000
True cost per chart
OE
$0.0004
Credit API
$0.0950
REST API
$0.0022
Predictive charts included
OE
15,000
Credit API
~125
REST API
0
Compute engine
OE
JPL DE440
Credit API
Swiss Ephemeris
REST API
Static lookups
LLM-optimized output
OE
✓ format=llm
Credit API
✗
REST API
✗
Overage policy
OE
Opt-in, capped
Credit API
Hard 429 crash
REST API
Hard 429 crash
* “100,000 credits” at a competitor typically yields ~200 basic charts due to 500-credit penalty pricing per chart. OpenEphemeris: 1 standard chart = 1 credit. Predictive operations (transits, returns) cost 5 credits each. Astrocartography costs 10 credits. All numbers based on publicly listed pricing as of March 2026.
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.
What counts as 1 credit?+
One standard computation—natal chart, lunar phase, dignity check, timezone resolution, or an LLM-optimised response. Predictive math costs 5 credits—transit search is included on the free Explorer tier, while returns and progressions need Pro or higher. Comparative/synastry costs 3 credits (Pro and up). Visual rendering (SVG/PNG) costs 2 credits and works on every tier, including Explorer. Astrocartography costs 10 credits (Pro and up). Calendar costs 10 credits. Human Design costs 2 credits.
Can I test this quickly?+
Yes. Read the public docs first, then sign up for the free Explorer tier (150 credits, one-time — credits never expire) and start making live requests. No credit card required.
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.