How to Choose an Astrology API

Full disclosure up front: we built OpenEphemeris, and it is one of the five options in this comparison. We are not neutral. What we can be is specific — every claim here is something you can verify yourself against public docs and pricing pages in under an hour, and where a competitor is genuinely better for your use case, we say so.

"Best astrology API" does not have one answer. It has an answer that depends on what you are building: a Vedic app for an existing sidereal audience, an AI agent that needs to reason about a chart, a desktop tool that has to run offline, or a SaaS product trying to avoid a licensing headache three years from now. This guide walks through the dimensions that actually decide it, then gives you a decision framework instead of a rigged ranking.

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The Five Options

OpenEphemeris — hosted REST API, 119 endpoints, computed directly from the NASA JPL DE440 ephemeris kernel. Covers Western, Vedic, BaZi (Chinese four-pillars), and Human Design in one account.

astrologyapi.com — one of the longest-running astrology APIs on the market, with a large, established Vedic-first developer base and a wide catalog of endpoint types.

Prokerala — a Vedic-astrology-focused API and content platform with broad Hindu/Vedic system coverage (panchang, dashas, muhurta) that goes deeper into that tradition than most Western-first APIs attempt.

Self-hosted Swiss Ephemeris (swisseph) — not an API at all, but the C library most astrology software is actually built on underneath. You compile it, host it, and own the whole stack. We wrote a full comparison if this is on your shortlist.

RapidAPI astrology listings — a marketplace, not a single vendor. Dozens of astrology endpoints from different third-party publishers, of wildly varying quality, freshness, and support — worth knowing about, hard to generalize about.

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Data Source & Precision

Every option on this list will get you a usable chart. The question is what sits underneath the number.

OpenEphemeris computes positions directly from the NASA JPL DE440 kernel — the same series JPL publishes for spacecraft navigation — to sub-arcsecond precision across 1550–2650 CE. Swiss Ephemeris reproduces JPL data (DE441 as of its current release) to 0.001 arcsec from a compressed ~97 MB file, and covers a dramatically wider span — roughly 13,201 BCE to 17,191 CE — a genuine win if your app needs historical or far-future dates outside OpenEphemeris's range. For any date both cover, the two are effectively equivalent in accuracy; the real differences are delivery model and range, not precision.

We have not independently verified the underlying ephemeris precision or historical date range of astrologyapi.com, Prokerala, or individual RapidAPI listings, and we are not going to guess at numbers we cannot confirm. If precision or exact date coverage matters to your application, ask the vendor directly what ephemeris source and epoch range they compute from before you build on it — a surprising number of astrology APIs do not publish this.

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Systems Breadth: the real differentiator

This is where the field splits sharply. Most astrology APIs — including most RapidAPI listings — are Western-tropical only, with maybe a basic sidereal toggle bolted on. Prokerala and astrologyapi.com go the other direction: deep, well-established Vedic coverage (dashas, panchang, nakshatras, muhurta) built for a Vedic-first audience that has used them for years.

OpenEphemeris covers four full systems in one account: Western tropical (7 house systems), Vedic/sidereal (Lahiri and other ayanamsas, nakshatra placements), BaZi (Chinese four-pillars), and Human Design (bodygraph, type, authority, channels). If your product needs to serve more than one tradition — or you don't yet know which one your users will ask for — that breadth means one integration instead of three. If you are building specifically and only for a Vedic-first audience, astrologyapi.com and Prokerala have a longer track record in that exact space, and that entrenchment is worth something: more community content, more Stack Overflow answers, more precedent.

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LLM & Agent Readiness

This is the dimension that did not exist as a buying criterion two years ago and now matters immediately if you are building anything AI-facing.

OpenEphemeris ships a ?format=llm query parameter on every endpoint that returns the same chart data condensed for a language model — roughly 500–800 tokens instead of 4,000–8,000 for a full natal chart. It also runs a maintained MCP server (92 tools, Model Context Protocol) that Claude, Cursor, ChatGPT, Gemini CLI, and other MCP-compatible agents can call directly, plus a custom connector you can add to claude.ai in about two minutes — no API key required to connect. As far as we can find in any of these vendors' public documentation, none of the other four options in this comparison offer an equivalent token-optimized response format or a maintained MCP server. If that turns out to be wrong, or a competitor ships one, we will update this post — this is the kind of claim we do not want to overstate.

If you are building an AI agent that needs to reason about a chart rather than just render one, this is probably the single biggest practical difference between OpenEphemeris and the rest of this list.

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Pricing Floor

Quoting our own numbers verbatim, since they are the ones we can vouch for completely: 150 credits to start (one-time), no card required. That is a one-time wallet grant, not a renewing monthly allowance — it does not reset, and credits never expire. From there, wallet top-ups start at $5 for 150 credits, and subscription plans start at $29/mo for 75,000 credits with production-scale rate limits.

We are not going to reproduce astrologyapi.com's, Prokerala's, or any RapidAPI listing's current pricing here — published tiers change, and quoting a stale number would be worse than not quoting one. Check their pricing pages directly; what we can tell you is the pattern to watch for regardless of vendor: some astrology APIs meter in "credits" but charge a steep credit cost per calculation type (a single predictive chart costing far more than a basic natal chart), which makes the sticker price misleading until you do the per-operation math. Ask what a synastry chart or a transit search actually costs in whatever unit the vendor bills in, not just what the plan advertises.

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Rate Limits

OpenEphemeris scales rate limits with plan tier: 30 requests/minute on the free Explorer tier, 180/min on the $29/mo Pro tier, up to 1,000/min on the Scale tier. Self-hosted Swiss Ephemeris has no rate limit at all in the traditional sense — it is a local library call, bounded only by your own hardware — which is a genuine advantage for latency-sensitive or offline use.

We don't have verified current rate-limit figures for astrologyapi.com, Prokerala, or individual RapidAPI publishers to quote here; check the specific plan you're evaluating.

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Licensing & the Self-Host Route

If you would rather own the whole stack than call a hosted API, Swiss Ephemeris is the library nearly everyone else's software is built on somewhere in the chain. It is dual-licensed: free under AGPL v3, or a one-time CHF 700 professional license from Astrodienst. The AGPL path matters more than it looks — Section 13 extends the copyleft obligation to network use, so a SaaS product built on the free license generally has to offer users its complete source. The professional license removes that obligation. Either way, you compile the C library yourself (or use a Python, Java, PHP, Perl, Node, or R wrapper) and own hosting, scaling, and updates. Our fuller breakdown, including the pyswisseph wrapper-licensing wrinkle, is in the Swiss Ephemeris comparison.

Hosted APIs — OpenEphemeris included — sidestep the AGPL question entirely because you never link the library yourself; you're licensing computation, not code, under the vendor's commercial API terms. That is the trade a hosted API always makes: less licensing friction, in exchange for a network dependency and a bill.

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Comparison at a Glance

Dimension	OpenEphemeris	astrologyapi.com	Prokerala	Swiss Ephemeris (self-host)	RapidAPI listings
Delivery	Hosted REST API	Hosted REST API	Hosted REST API	C library, self-hosted	Marketplace, varies by publisher
Systems	Western, Vedic, BaZi, Human Design	Vedic-first, Western	Vedic-focused (deep)	Western, Vedic (build it yourself)	Varies widely
LLM/agent support	format=llm + MCP server (92 tools) + claude.ai connector	Not found in public docs	Not found in public docs	None — you build the integration	Varies, generally none
Free tier	150 credits, one-time, no card	Varies — check current pricing	Varies — check current pricing	Free under AGPL v3	Varies by listing
Licensing	Commercial API terms	Commercial API terms	Commercial API terms	AGPL v3 or CHF 700 license	Varies by publisher
Offline / self-hosted	No	No	No	Yes	No

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How to Actually Decide

Skip the ranking and ask these in order:

1. Do you need more than one astrological system? If yes, and Vedic isn't your only need, OpenEphemeris's four-system coverage avoids a second integration later. If you're Vedic-only and want the deepest bench of Vedic-specific endpoints and community precedent, astrologyapi.com or Prokerala are the more battle-tested choice.
2. Is the consumer an AI agent, or a human via a UI? If an LLM is calling this API — a chatbot, an agent workflow, anything reasoning over the chart — the token-optimized format and MCP tooling narrow this to one real option today.
3. Can you tolerate a network dependency? If you need offline operation, air-gapped compute, or zero per-call latency, nothing here beats self-hosted Swiss Ephemeris — that's not a knock on hosted APIs, it's just a different deployment shape.
4. What's your AGPL tolerance? If your product is closed-source and you don't want to evaluate copyleft exposure, a commercially-licensed hosted API removes the question. If you're already open-source or comfortable with the CHF 700 license, self-hosting is the cheapest unlimited compute you'll find.
5. What does a real calculation actually cost? Not the plan price — the per-operation cost for the specific calculation type your product calls most. Do that math for every vendor you're seriously considering, ourselves included.

None of these questions have a universally right answer. They have a right answer for what you're building. If that answer is OpenEphemeris, the free tier costs nothing to try — 150 credits, no card, enough to build and test a real integration before you decide anything.