Comparison · For developers
Swiss Ephemeris vs OpenEphemeris
Swiss Ephemeris is the industry-standard astronomical library — 25 years in production, the de facto accuracy reference, and the engine behind most astrology software ever shipped. OpenEphemeris is a hosted API. Which one you want depends on what you're building, and for plenty of projects the honest answer is Swiss Ephemeris. Here's the full picture.
The short version
Choose Swiss Ephemeris if…
- You're building offline or desktop software — a local C library beats any API
- You need dates outside 1550–2650 CE (Swiss covers ~13,201 BCE to 17,191 CE)
- You need 385,000+ numbered asteroids, hypothetical/Uranian points, or heliacal events
- You're a C/Python shop comfortable self-hosting and managing ephemeris files
- Your app is AGPL-compatible, or a CHF 700 one-time license fits your budget
Choose OpenEphemeris if…
- You're building SaaS, a web app, or AI agents and want zero AGPL exposure
- You'd rather not run, patch, and scale calculation infrastructure yourself
- You want an MCP server (90 tools) so Claude and other agents can compute charts directly
- You want higher-level endpoints — charts, synastry, astrocartography, Human Design, Vedic, electional — not just raw positions
- You want to start free (150 credits, no credit card) and pay as you grow
Side by side
Feature-by-feature comparison
Both are JPL-grade. Where Swiss Ephemeris is simply better, the table says so.
| Dimension | Swiss Ephemeris | OpenEphemeris |
|---|---|---|
| Licensing model | Dual: AGPL v3, or CHF 700 one-time professional license | Commercial API terms — no AGPL, no license contract to sign |
| Data source | Compressed JPL data (DE441 as of v2.10.3), ~97 MB | NASA JPL DE440 kernel, used directly (uncompressed) |
| Precision | Reproduces JPL to 0.001 arcsec | Sub-arcsecond against JPL DE440 |
| Time range | 13,201 BCE – 17,191 CE (~30,000 years) — a clear Swiss win | 1550 – 2650 CE |
| Bodies | 385,000+ numbered asteroids, hypothetical/Uranian points, fixed stars — a clear Swiss win | 70+ bodies, 110+ fixed stars — the set most charts actually use |
| Delivery | C library you compile and host; wrappers for Python, Java, PHP, Perl, Node, R | Hosted REST API (118 endpoints) + MCP server (90 tools) |
| Latency model | Zero network latency, fully offline — a clear Swiss win for local compute | Network round-trip per call; no cold-start infra on your side |
| AI / MCP support | None official — you build the integration layer yourself | First-class: MCP server for Claude/Cursor/Gemini, format=llm token-optimized output |
| Cost model | Free under AGPL, or CHF 700 one-time; zero marginal cost at volume | Free trial (150 credits, one-time), then metered credits or subscription |
| Maintenance burden | You own builds, ephemeris files, updates, scaling, and correctness testing | None — hosted, monitored, versioned; you consume JSON |
The part that actually decides it
Licensing, in plain terms
The AGPL network clause
Swiss Ephemeris's free license is the AGPL v3, and the clause that matters for web developers is Section 13. The ordinary GPL only obligates you when you distribute binaries; the AGPL extends that trigger to network use. If users interact with your application over a network — every SaaS, every web app, every hosted API — you must offer them the complete corresponding source of that application under the AGPL.
In practice, for a SaaS product this means open-sourcing the application that links swisseph. For an open-source project that's a feature, not a bug — plenty of excellent AGPL-licensed astrology software exists. For a proprietary product it's usually a dealbreaker, which is why Astrodienst offers a commercial alternative.
The professional license
The Swiss Ephemeris Professional License (June 2026 contract edition) is CHF 700, one-time, for a single unlimited license: 99-year term, no royalties, no per-chart fees, and the contract explicitly covers server and SaaS use. As a one-time cost for unlimited volume, that is genuinely good value — if you're happy self-hosting, it's the cheapest unlimited compute you'll ever buy. Know what you're signing, though: it's a paper contract with Astrodienst AG, support is a community mailing list, there's no warranty of calculation correctness, and you may not mention Astrodienst or the authors in your marketing without written permission.
The wrapper question
One genuinely unsettled area: pyswisseph, the most popular Python wrapper, is published on PyPI as AGPL-3.0-only (last release June 2023). Whether a purchased professional license for the underlying C library fully cures the licensing of an AGPL-only wrapper is an open question in the community — not something either side has definitively resolved. If your stack goes through a wrapper, it's worth raising with Astrodienst before you build on it.
OpenEphemeris sidesteps all of this by not using Swiss Ephemeris at all: positions are computed directly from the NASA JPL DE440 kernel, which is public-domain US government data. There is no AGPL in the chain, no contract to sign, and no per-chart fee — you pay for hosted computation, metered in credits.
Frequently Asked Questions
Can I use Swiss Ephemeris in a commercial app?+
Yes, two ways. Either release your application under the AGPL v3 (including offering complete source to users who access it over a network), or purchase the Swiss Ephemeris Professional License — a one-time CHF 700 contract with Astrodienst AG covering commercial use, including server and SaaS deployment, with no per-chart fees.
Do I have to open-source my app if I use Swiss Ephemeris?+
Under the free AGPL v3 license, effectively yes for SaaS: AGPL Section 13 requires that anyone interacting with your application over a network be offered its complete corresponding source under the AGPL. The paid professional license removes that obligation. If neither works for you, a separately-licensed hosted API avoids the question entirely.
How much does the Swiss Ephemeris professional license cost?+
As of the June 2026 contract edition: CHF 700, one-time, for a single unlimited license with a 99-year term and no royalties or per-chart fees. It is a signed paper contract with Astrodienst AG. Practical terms to know: support is a community mailing list, there is no warranty of calculation correctness, and you may not reference the authors in your marketing without written permission.
Is there a Swiss Ephemeris API?+
Not an official one — Astrodienst does not offer a hosted REST API for Swiss Ephemeris. You compile the C library (or use a wrapper for Python, Java, PHP, Perl, Node, or R) and host it yourself. OpenEphemeris exists to fill that gap: a hosted, commercially-licensed ephemeris API with the same underlying JPL-grade accuracy.
Does running Swiss Ephemeris on my server avoid the AGPL?+
No — that is exactly the case the AGPL was written for. Unlike the plain GPL, AGPL Section 13 treats network access as distribution: if users interact with your swisseph-linked application over a network, you must offer them its complete source. Running it server-side does not exempt you; it triggers the clause.
How accurate is OpenEphemeris compared to Swiss Ephemeris?+
They are effectively equivalent — accuracy is not the differentiator. Both reproduce NASA JPL ephemeris data to sub-arcsecond precision (Swiss Ephemeris to 0.001 arcsec from compressed JPL files; OpenEphemeris directly from the DE440 kernel). For any astrological purpose the positions agree. The real differences are delivery model, licensing, time range, and body coverage.
Decided on the hosted route?
118 endpoints, NASA JPL DE440 precision, zero AGPL exposure. And if you decided on Swiss Ephemeris instead — good choice too.
Explore the full astrology API or evaluate Swiss Ephemeris yourself.