Our own clean-room Rust engine computes from NASA JPL DE440 and is verified against JPL Horizons to under 0.003″.
Use it through the REST API, or install it yourself.
Every suite below compares the engine with an outside reference. Errors are the largest difference found, in arcseconds (″) unless noted. Figures come from the engine's acceptance report for version 1.0.0.
| Suite | Reference | Vectors | Largest error | Pass limit |
|---|---|---|---|---|
| l1a_horizons_de440 | JPL Horizons DE440 positions | 360 | 0.002975″ | < 0.005″ |
| l1b_planets_de440s | DE440s with IAU 2006/2000A (SOFA) | 90 | 0.000527″ | ≤ 0.01″ |
| l1b_asteroids_68 | JPL Horizons SB441-N16 with IAU 2006/2000A | 340 | 0.000006″ | ≤ 0.05″ |
| l1b_ayanamsas_12 | Lieske (1977), IAE (1989), Hipparcos-2 | 120 | 0.000000″ | ≤ 0.05″ |
| l1b_houses_23 | Holden (1977) and Munkasey (1991): 23 systems, angles and Gauquelin sectors | 253 | 0.000000″ | ≤ 0.01″ |
| l1b_lunar_points_7 | ELP-2000/82B and DE440s apogee | 63 | 0.000025″ | ≤ 0.05″ |
| l1b_uranians_9 | Witte, Sieggrün and Seov models | 54 | 0.000018″ | ≤ 0.05″ |
| l1b_stars_50 | VizieR Hipparcos-2, XHIP and SOFA | 104 | 0.000263″ | ≤ 0.01″ |
| l3_se_reference | Swiss Ephemeris black-box cross-check | 250 | 1.1402″ planets, 0.000000″ houses | Documented budget |
| l3_se_10k_grid | Full-domain grid, years 1850 to 2100 | 10,242 | 0.000486″ planets, 0.000254″ minor bodies | All sections verified |
| l3_wave_bcf_10k_grid | Events, lunar phases, solar terms, ayanamsas, house positions | 10,540 | 0.0005″ ayanamsas, events below 1e-9° | All sections verified |
| l3_wave_g_extreme_10k_grid | Extreme boundaries and SWE-01..SWE-11 regression guards | 10,000 | 0 bug regressions | All guards verified |
The under 0.003″ claim rests on the first row, which compares against JPL Horizons. The l3_se_reference row measures agreement with Swiss Ephemeris output as a compatibility budget. It is not an accuracy claim.
A side-by-side look at observable differences. We list behaviors, not marketing numbers, and we publish no latency comparison until a fair head-to-head benchmark exists.
| Feature | Lx Ephemeris | Swiss Ephemeris |
|---|---|---|
| Core language | Rust, forbid(unsafe_code) | C library (libswe) |
| Data source | NASA JPL DE440 (native DE440s kernel) | DE431-based compressed .se1 files |
| Missing data files | Engine() runs with zero files in built-in analytical mode; loading a kernel directory raises an error if files are missing | Can fall back silently from .se1 to an analytical series |
| Polar houses | Explicit PolarPolicy: error or labelled fallback | Silent fallback to Porphyry cusps above about 66.56° latitude |
| Star-anchored ayanamsas | No yearly aberration wobble | About ±20.5″ annual wobble |
| Minor bodies setup | 68 JPL minor bodies from one verified kernel file | Separate .se1 files to manage |
| Event solvers | Built-in transit, return, station and Void-of-Course Moon solvers | Write your own search loops |
| Shared state | Immutable engine, no process-global state | Process-global settings for sidereal mode, observer and path |
| SDKs | Python, Node.js, Rust and CLI with identical math | C library plus separate third-party bindings |
Three ways to use the engine in a commercial product. Pick the one that fits how you deploy.
Turnkey cloud REST API
Commercial use is included and there is no engine license to buy. You also get geocoding, historical timezone resolution, SVG chart wheels and interpretations.
Self-hosted Lx Ephemeris
For running the engine on your own servers inside products you ship to end users.
For API and platform businesses
Required for any B2B developer API, Ephemeris-as-a-Service, SDK, webhook, MCP or passthrough service. The Standard Commercial License does not allow these.
A signed Ed25519 key is verified locally, with zero network calls at runtime.
Pass the key as an environment variable or a mounted secret file in Docker and Kubernetes.
Production never expires, and numerical behavior never changes after the updates_until date.
Python, Node.js, Rust and the CLI return identical results.
Companies can test in non-production environments for 30 days before they buy.
Personal, academic and non-profit use stays free under PolyForm Noncommercial.
Lx Ephemeris runs behind every calculation endpoint. See it in action with the Natal Chart API — full birth charts; Transit API — real-time planetary timing; Vedic Astrology API — sidereal charts and dashas; House Systems API — 23 house systems with polar handling; Fixed Stars API — 52 fixed stars.
Numbers from the engine's own acceptance report, version 1.0.0
The clean-room Rust engine that does the sky math inside Astrology API
What is Lx Ephemeris? Lx Ephemeris (lxephemeris on PyPI, npm and crates.io) is the calculation engine at the core of Astrology API. You give it a moment in time and a place on Earth. It gives back planet positions, house cusps, aspects, fixed stars, eclipses and a long list of other astrological values. It is a clean-room Rust engine: it was written from published astronomy standards, with no Astrodienst code. It reads NASA JPL DE440 data and applies the IAU 2006/2000A precession and nutation models. Our own clean-room Rust engine, Lx Ephemeris, computes from NASA JPL DE440 with IAU 2006/2000A models — no Astrodienst code — verified against JPL Horizons to under 0.003″, with explicit handling of edge cases where Swiss Ephemeris silently degrades. This page explains how the engine works, what we changed compared with Swiss Ephemeris, how you can check every number yourself, and which license you need if you want to run it on your own servers. If you only want the finished results, the Astrology API REST endpoints already use it. A Pro subscription is $11/month, and the free tier is 50 requests every month.
Lx Ephemeris is a software library that answers one question very precisely: where is everything in the sky at a given moment, and what does that mean in astrological terms? It is written in Rust.
It reads JPL DE440 planetary data, the same family of data NASA uses, and turns it into positions you can use in an app.
In one engine you get the planets, 68 JPL minor bodies, 52 fixed stars, 23 house systems and 43 sidereal ayanamsas.
On top of that it ships event solvers for transits, returns, stations and the Void-of-Course Moon, plus eclipses and occultations.
It also covers Vedic Panchanga, divisional charts and Vimshottari Dasha, Traditional sect, planetary hours and Hermetic lots, Human Design gates and the Chinese Solar Terms.
Before this engine, a typical backend glued several libraries together to get the same list.
Lx Ephemeris replaces that stack with one dependency that has identical math in Python, Node.js, Rust and a command-line tool.
We replaced it because of four documented behaviors (SWE-01, SWE-06, SWE-07, SWE-02), not because of a grudge.
Swiss Ephemeris has served astrologers for decades, and it is still the best-known name in the field.
First, it keeps settings such as the sidereal mode, the topocentric observer and the ephemeris path in process-global state.
One request that switches to Lahiri can change the zodiac for another request running at the same time, unless you serialize every call behind a lock.
Second, when a requested .se1 data file is missing, it can quietly fall back to a lower-precision analytical series and return slightly different longitudes with no exception.
Third, at polar latitudes house calculation can silently swap the system you asked for with Porphyry cusps, or return a flipped Ascendant.
Fourth, star-anchored ayanamsas include a yearly aberration wobble of about ±20.5″.
Lx Ephemeris is built so that none of these can happen: the engine is immutable, a missing kernel directory raises an error, and polar behavior is an explicit policy that you choose.
Our own clean-room Rust engine, Lx Ephemeris, computes from NASA JPL DE440 with IAU 2006/2000A models — no Astrodienst code — verified against JPL Horizons to under 0.003″, with explicit handling of edge cases where Swiss Ephemeris silently degrades.
The number comes from a golden-vector test: the engine's positions are compared against 360 reference positions from JPL Horizons, and the largest error is 0.002975″.
Other suites check planets against the IAU SOFA routines, the 68 minor bodies against JPL Horizons small-body kernels, house cusps against published formulas for all 23 systems, and fixed stars against the Hipparcos-2 catalog.
The full per-suite table is shown below this section.
The <0.003″ figure applies to DE440 kernel mode.
The built-in analytical mode is a fileless convenience with looser limits.
We only claim higher precision where we can name the exact case: star-anchored ayanamsas, polar houses, light deflection near Jupiter and Saturn, and the silent .se1 fallback.
We do not claim a blanket win over any other library.
Five divergences matter most to people building apps.
SWE-02: star-anchored ayanamsas such as True Citra, True Revati and True Pushya no longer wobble by ±20.5″ over the year, because the anchor star is propagated without annual aberration.
SWE-03: the house-position function can no longer return 0.0, which is not a valid house, for a body near the circumpolar limit in Koch and Placidus; you always get a position between 1 and 13.
SWE-04: a star lookup for Mira can no longer resolve to Mirach, which could shift the answer by more than 17° of longitude, because names are matched exactly.
SWE-06: a missing or corrupt kernel raises a clear error, while fileless analytical mode has to be requested on purpose.
SWE-07: above about 66.56° latitude you pick a PolarPolicy, so you get an error or a labelled fallback instead of a silent change.
Planet positions also include Jupiter and Saturn light deflection, worth 0.002–0.017″ near their conjunctions.
It depends on how you use it.
If you call the Astrology API REST endpoints, you do not need any engine license.
Commercial use is included in your subscription, and there is no AGPL obligation for API users.
If you self-host the engine inside a commercial product, you need the Lx Ephemeris Commercial License.
Lx Ephemeris is source-available under the PolyForm Noncommercial 1.0.0 license, so personal projects, academic research, education and non-profits can use it free of charge.
Companies can also test it in a non-production environment for up to 30 days before buying.
The Standard Commercial License covers end-user apps, content platforms and internal business systems.
A B2B developer API, Ephemeris-as-a-Service, SDK, webhook, MCP or passthrough service needs a separate Enterprise / API Provider Agreement.
The commercial section further down this page has a short request form.
Install it from the package manager you already use: pip install lxephemeris for Python, npm i lxephemeris for Node.js, or the lxephemeris-core crate for Rust.
There is also a command-line tool.
All of them share the same math, so a Python result and a Rust result agree to the last bit.
Engine() works with zero external files through its built-in analytical mode.
For full precision you load a NASA JPL DE440s kernel directory instead, and if the files are missing or corrupt, loading it raises an error rather than falling back silently.
The engine checks the files against a SHA-256 manifest when it loads.
The <0.003″ figure applies to this DE440 kernel mode.
A full natal chart snapshot with planets, houses, aspects, Hermetic lots, lunar phase and sect runs in roughly 150–240 µs, and a single body with speed takes about 12.8 µs.
If you already have code written for pyswisseph, a drop-in adapter lets you migrate without rewriting every call site.
If you would rather not run any of this yourself, the REST API gives you the same engine with geocoding and timezones included.
Call the REST API and get Lx Ephemeris results with geocoding, historical timezones and SVG charts. Commercial use is included.
Run the engine on your own servers or on-premise with a Standard Commercial License and an offline license key.
Use the engine free of charge for academic research, teaching and non-profit work under PolyForm Noncommercial.
Move an existing pyswisseph codebase to Lx Ephemeris with a drop-in adapter and keep your call sites.
Panchanga, divisional charts, Vimshottari Dasha and 43 ayanamsas from one engine, with star-anchored ayanamsas that do not wobble.
Charts for Svalbard, northern Scandinavia or Antarctica use an explicit polar policy instead of a silent fallback.
| Core language | Rust, memory-safe (forbid(unsafe_code)) |
| Data source | NASA JPL DE440 (DE440s kernel) |
| Models | IAU 2006/2000A precession and nutation |
| Precision | <0.003″ vs JPL Horizons DE440 |
| Single body with speed | 12.8 µs |
| Full natal chart | ~150–240 µs |
| House systems | 23, with explicit polar policies |
| Sidereal ayanamsas | 43 |
| JPL minor bodies | 68 |
| Fixed stars | 52 |
| SDKs | Python / Node.js / Rust SDKs, plus a CLI |
| Packages | lxephemeris (PyPI), lxephemeris (npm), lxephemeris-core (crates.io) |
| License | PolyForm Noncommercial 1.0.0 or Commercial License |
| License activation | Offline Ed25519 key, zero network calls at runtime |
Full birth charts powered by Lx Ephemeris
Real-time planetary transits
Sidereal charts, dashas and nakshatras
23 house systems with polar handling
52 fixed stars with proper motion
Raw planet coordinates on demand
One engine, four areas
Start free, scale as you grow. No hidden fees, no surprises.
For small apps and personal projects
For growing apps and medium traffic
For enterprise-scale applications
All plans include comprehensive documentation and SDKs
Questions? Talk to our team
Straight answers about the engine, its accuracy and its license