TL;DR

Swiss Ephemeris is licensed under AGPL, which requires any network-accessible app using it to release its full source code under the same license.
A commercial license from Astrodienst removes the AGPL obligation, but pricing is not public.
Wrapping Swiss Ephemeris in a microservice does not necessarily isolate your main app from AGPL requirements.
Cloud-based astrology APIs with no AGPL restrictions let you ship proprietary SaaS products without license risk.

About the author: Brett Calloway is a Developer Advocate and AI Integration Specialist with 12 years of experience building APIs and developer tooling, including three years focused on AI-native infrastructure for spiritual and wellness applications. He has led developer relations at two Series B SaaS companies and spoken at PyCon and JSConf on building context-rich AI agents using Model Context Protocol.

If you are building a commercial astrology application, you will almost certainly encounter Swiss Ephemeris during your research. It is the gold standard library for planetary position calculations, and most desktop astrology software relies on it. But the moment you deploy it inside a SaaS product, web app, or public API, you face a licensing decision that can force you to open source your entire codebase. Understanding Swiss Ephemeris AGPL licensing is not optional for SaaS developers. It is a compliance requirement that determines your architecture.

What is Swiss Ephemeris and why does it matter

Swiss Ephemeris is a high-precision astronomical calculation library created by Astrodienst, the company behind astro.com. It computes planetary positions, house cusps, eclipses, and other astronomical data used in astrological chart generation. The library draws on the NASA JPL Development Ephemeris (DE431) and achieves sub-arcsecond accuracy across thousands of years. For desktop astrology software, it has been the default choice for over two decades. Most established astrology applications on Windows, macOS, and Linux use Swiss Ephemeris under the hood. Its accuracy and breadth of astronomical functions make it the benchmark that other calculation libraries are measured against. If you are evaluating ephemeris options for a new project, you will find Swiss Ephemeris referenced in virtually every astrology developer forum and comparison thread.

How the AGPL license affects your SaaS application

Swiss Ephemeris is dual-licensed. The free license is AGPL v3 (GNU Affero General Public License). The AGPL was designed specifically to close the "SaaS loophole" that existed in the standard GPL. Under standard GPL, you only need to share source code when you distribute binaries. AGPL extends this obligation to network use. If users interact with your software over a network (through a browser, API call, or mobile app connecting to your server), you must make your complete source code available under AGPL. This means your entire application, not just the Swiss Ephemeris wrapper code. Every file in your repository that links to or depends on the AGPL-licensed component falls under the same requirement. For a SaaS product, this effectively means publishing your full backend codebase, including your business logic, authentication system, billing code, and proprietary algorithms.

Ready to build this? Roxy Astrology API gives you accurate natal charts, planetary positions, and aspects with no AGPL restrictions on your side. See pricing.

The commercial license alternative from Astrodienst

Astrodienst offers a proprietary commercial license for Swiss Ephemeris that removes the AGPL obligation entirely. With a commercial license, you can use Swiss Ephemeris in closed-source products without any source code disclosure requirements. However, the pricing for this license is not publicly listed on their website. You need to contact Astrodienst directly to discuss terms. The cost varies based on your use case, deployment scale, and revenue model. For funded startups and established companies, the commercial license is a clean solution. For indie developers, early-stage projects, or teams that want to avoid vendor lock-in on a calculation dependency, the licensing negotiation and recurring cost add friction to the build process. Before committing to Swiss Ephemeris for a commercial product, factor in the time and budget required to secure and maintain this license.

Common misconceptions developers have about AGPL

Several misunderstandings circulate in developer communities about how AGPL applies in practice. The first is that server-side-only use exempts you from AGPL. This is incorrect. AGPL was created precisely to cover server-side deployments where users never receive a binary. If your server uses Swiss Ephemeris and responds to HTTP requests, AGPL applies.

The second misconception is that wrapping Swiss Ephemeris in an isolated microservice protects your main application. The legal argument here is nuanced. If your microservice exists solely to serve Swiss Ephemeris calculations and your main app calls it over HTTP, you may be creating a derivative work. Courts and legal scholars have not settled this question definitively, and relying on architectural separation as a license compliance strategy carries real risk.

The third is that using the Swiss Ephemeris data files (the ephemeris tables) without the code avoids AGPL. The data files carry their own license terms, which you must review independently. They are not automatically free of restrictions just because they are data rather than code. Before building on any of these assumptions, consult a lawyer who specializes in open source licensing. The cost of legal review is far less than the cost of a forced open source disclosure or a license violation claim after launch.

When to use Swiss Ephemeris versus a cloud API

The right choice depends on your deployment model and business structure. Swiss Ephemeris is an excellent fit for three scenarios: open source projects where AGPL compliance is natural, desktop applications distributed as binaries where standard GPL terms may apply, and commercial products where you have budgeted for the proprietary license from Astrodienst. A cloud-based calculation API is the better fit for SaaS applications and web apps where you need proprietary source code, startups that cannot afford license exposure or negotiation overhead, mobile apps with server-side calculation backends, and AI agents or chatbots that call astrology tools over HTTP. The decision tree is straightforward. If your code touches a network and you want it proprietary, either pay for the commercial license or use an API that handles the calculations for you. Many teams discover this constraint after months of development, which makes the refactoring cost far higher than starting with the right architecture.

How astrology APIs eliminate AGPL risk for your app

Cloud-based astrology APIs run their own calculation infrastructure. Your application sends a request and receives structured JSON. No AGPL-licensed code runs in your environment, and no license obligation transfers to your codebase. This is the same model developers use for payment processing, email delivery, and geocoding: delegate the specialized computation to a service, keep your application logic proprietary. You also gain operational benefits. The API provider handles ephemeris updates, leap second corrections, and accuracy validation. You consume verified results without maintaining astronomical calculation code in your own stack.

Here is a working example using Roxy Astrology API to generate a natal chart. The endpoint is POST /api/v2/astrology/natal-chart and requires a JSON body with birth date, time, coordinates, and timezone offset.

curl -X POST https://roxyapi.com/api/v2/astrology/natal-chart \
  -H "X-API-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "date": "1990-07-15",
    "time": "14:30:00",
    "latitude": 40.7128,
    "longitude": -74.006,
    "timezone": -5
  }'

The response includes planetary positions with zodiac signs and house placements, 12 house cusps, aspects between planets with orb and strength values, ascendant and midheaven data, and a chart summary with dominant element and modality distribution. Every field is typed and documented in the OpenAPI spec. No AGPL code runs on your servers. No license obligation touches your product.

{
  "birthDetails": {
    "date": "1990-07-15",
    "time": "14:30:00",
    "latitude": 40.7128,
    "longitude": -74.006,
    "timezone": -5
  },
  "planets": [
    {
      "name": "Sun",
      "longitude": 112.45,
      "sign": "Cancer",
      "degree": 22.45,
      "house": 7,
      "isRetrograde": false,
      "interpretation": {
        "summary": "Your Sun in Cancer in The Seventh House reveals how you express self-awareness and ego in the realm of partnerships.",
        "keywords": ["Nurturing", "Protective", "Emotional", "Intuitive"]
      }
    }
  ],
  "houses": [
    { "number": 1, "sign": "Taurus", "degree": 15.32 }
  ],
  "aspects": [
    {
      "planet1": "Sun",
      "planet2": "Moon",
      "type": "TRINE",
      "orb": 2.5,
      "strength": 75,
      "interpretation": "harmonious"
    }
  ],
  "ascendant": { "sign": "Taurus", "degree": 15.32 },
  "midheaven": { "sign": "Aquarius", "degree": 8.76 },
  "summary": {
    "dominantElement": "Water",
    "dominantModality": "Cardinal",
    "retrogradePlanets": ["Saturn"],
    "elementDistribution": { "Fire": 2, "Earth": 3, "Air": 1, "Water": 4 }
  }
}

All planetary positions are verified against NASA JPL Horizons. The response is deterministic and cache-friendly, with calculations backed by 828 gold standard tests cross-referenced against authoritative sources including DrikPanchang and timeanddate.com. You can also pass an optional houseSystem parameter to choose between Placidus, Whole Sign, Equal, or Koch house systems depending on the astrological tradition your app supports.

Frequently Asked Questions

Q: Does AGPL apply if I only use Swiss Ephemeris on my server and never distribute the binary? A: Yes. AGPL was specifically designed to cover network use. If users interact with your application over HTTP, you must provide the complete source code of your application under AGPL terms. Server-side-only deployment does not create an exemption.

Q: Can I isolate Swiss Ephemeris in a Docker container or microservice to avoid AGPL on my main app? A: This is legally uncertain. If the microservice exists solely to provide Swiss Ephemeris functionality to your application, a court could consider your main app a derivative work. Relying on architectural boundaries as a compliance strategy is risky without legal counsel.

Q: How much does the Swiss Ephemeris commercial license cost? A: Astrodienst does not publish pricing publicly. You must contact them directly to discuss terms. Cost depends on your deployment scale, use case, and revenue model. Budget time for the negotiation process in addition to the license fee.

Q: Is there an alternative to Swiss Ephemeris that avoids AGPL entirely? A: Yes. Cloud-based calculation services handle planetary computations on their own infrastructure. Your application calls the API over HTTP and receives JSON. No AGPL-licensed code runs in your environment, so no license obligation applies to your codebase.

Q: Are the Swiss Ephemeris data files (ephemeris tables) also covered by AGPL? A: The data files have their own license terms separate from the AGPL code license. Review the specific data file license before assuming they are free to redistribute or use commercially.

Making the right licensing decision for your astrology product

Swiss Ephemeris AGPL licensing is not a technicality you can architect around. If you are building a proprietary SaaS product, you need either the commercial license from Astrodienst or a calculation source that carries no AGPL restrictions. For most modern astrology applications, web services, AI agents, and mobile backends, an API-based approach is the path of least resistance. You keep full ownership of your code, avoid license compliance overhead, and ship faster. Explore the Roxy Astrology API for natal charts, planetary positions, daily horoscopes, synastry, and more. All plans include every domain and endpoint. See pricing.