If you searched for "Astrologer.com API," you probably landed on two different things: the educational consultancy at astrologer.com (Robert Currey, Correlation Journal), or — much more likely if you are a developer — the Astrologer API built on the open-source Kerykeion Python library by g-battaglia and distributed via RapidAPI. This article compares the second one against Astrology API.

We'll call them by their proper names: Kerykeion / Astrologer API for the RapidAPI service, and Astrology API for astrology-api.io.

Verified: May 10, 2026. Both products iterate often. Always confirm pricing on the vendor's RapidAPI listing or our own pricing page.

TL;DR

Attribute	Astrology API	Astrologer API (Kerykeion)
Calculation engine	Swiss Ephemeris + custom	Swiss Ephemeris via Kerykeion
Endpoint count	100+	~12 (chart + chart-data variants)
House systems	23	Roughly 9 (Placidus default + Whole-Sign, Equal, Koch, Regiomontanus, Campanus, Porphyry, Morinus, Topocentric)
Response time (avg)	~287ms	400–900ms (RapidAPI proxy overhead)
Free tier	50 req/mo, no card	Free tier on RapidAPI BASIC plan
Paid plans	$11 / $37 / $99 / $399+	Tiered on RapidAPI; specific monthly USD figures shown on the RapidAPI pricing page
AI interpretations	Yes (multilingual)	No native interpretations; AI-optimized XML context is exposed for your own LLM
Languages	9+ native	English primary; locale via library options
Output format	JSON	JSON + SVG charts
Multi-tradition	Western, Vedic, Chinese, Hellenistic	Western (tropical + sidereal), with planned extensions
Licensing	Commercial SaaS	Kerykeion library: AGPL-3.0; hosted API: closed-source-friendly when consumed via RapidAPI
Best fit	Production apps needing breadth + AI + speed	Open-source projects, indie devs, SVG-chart use cases

What each provider is

Astrology API is a commercial, multi-tradition astrology API that exposes 100+ endpoints across natal, transit, progression, synastry, composite, Vedic dashas, Chinese BaZi, Arabic parts, fixed stars, harmonic, and AI interpretation calls. It's a managed SaaS with its own infrastructure, billing, and dashboards. Pricing starts at $0 (free tier) and scales up to enterprise.

Astrologer API is the hosted version of Kerykeion, a Python astrology library by Giacomo Battaglia (g-battaglia on GitHub). The library is AGPL-3.0, which is why the hosted API exists: if you want to ship a closed-source app, you can't link AGPL code directly, but you can call the hosted API as a third-party service. The hosted API runs on RapidAPI's marketplace and is built around the Kerykeion engine. It returns both JSON data and SVG chart files, which is a real strength for apps that want to render charts without doing the SVG generation themselves.

Both products use Swiss Ephemeris under the hood. The accuracy ceiling is therefore similar. The differences show up in surface area, latency, ergonomics, and the breadth of techniques you can use without building your own logic on top.

Pricing in detail

Astrology API pricing (from our pricing page):

Free: $0/mo — 50 requests, no credit card
Starter: $11/mo — 1,000 requests
Professional: $37/mo — 55,000 requests
Business: $99/mo — 220,000 requests, all endpoints
Enterprise: $399+/mo — custom, dedicated infrastructure

Billing is direct, in USD, with monthly invoices and the ability to set hard caps. No credit-system math: 1 API call = 1 request, regardless of endpoint complexity. That predictability matters when one chart endpoint can blow your monthly budget on a credit-priced API.

Astrologer API pricing is tiered on RapidAPI. The Kerykeion docs (kerykeion.net and the project's GitHub) state that pricing tiers are listed on the RapidAPI subscription page at rapidapi.com/gbattaglia/api/astrologer/pricing. Specific monthly USD figures rotate as the project iterates, so we'll point you there rather than print a number that might be wrong by next week. As of May 10, 2026, the project explicitly says: "If you need higher quotas or a custom plan beyond the default tiers, reach out via kerykeion.astrology@gmail.com." That's accurate — verified directly from the project README.

The pricing model is request-based, with monthly quotas per RapidAPI tier. RapidAPI handles your billing in USD; the project receives revenue minus RapidAPI's fees. The hosted API exists in part to keep development funded, since the library itself is free.

Practical pricing differences:

Predictability. Astrology API uses flat request counts. Astrologer API uses RapidAPI's quota model, which is also request-based but routed through RapidAPI's billing.
Marketplace tax. RapidAPI takes a cut from every paid call routed through the marketplace, so the per-request price tends to be higher than direct vendor billing.
Add-on costs. Astrology API includes AI interpretations in higher tiers. The Astrologer API exposes AI-optimized XML context, but you bring your own LLM and pay for tokens separately.

If predictability of monthly spend matters more than anything else, direct billing wins. If you're already on RapidAPI and want to consolidate vendors there, the Astrologer API fits cleanly.

Endpoint coverage

Astrology API surfaces over 100 endpoints organized by tradition and technique:

Natal calculations: birth chart, dignities, sect, hemisphere/quadrant emphasis, chart shape, midpoints, parts of fortune and spirit, 97+ Arabic parts, fixed-star conjunctions
Time-based: transits, secondary progressions, solar arc directions, primary directions, profections, zodiacal releasing, solar return, lunar return
Synastry & composites: synastry aspects, composite (midpoint) charts, Davison relationship charts, marriage compatibility
Harmonic & specialty: harmonic charts (n-th harmonic), asteroids (Ceres, Pallas, Juno, Vesta, Chiron), Lilith (true/mean/black), centaurs, TNOs
Vedic: Vimshottari and other dashas, divisional charts (Navamsa, Dasamsa, etc.), nakshatras, Vargottama planets, planetary friendships
Chinese: BaZi (Four Pillars), Zi Wei Dou Shu basics
Mundane & electional: planetary hours, void-of-course Moon, retrograde watch, moon ingress
AI interpretations: natal report, daily/weekly/monthly horoscope, synastry interpretation, transit briefings — multilingual

Astrologer API exposes a tighter set, driven by what Kerykeion supports natively. From the v5 README:

/api/v5/chart/birth-chart — natal chart (JSON + SVG)
/api/v5/chart/synastry — two-person comparison
/api/v5/chart/transit — current-moment transits
/api/v5/chart/composite — midpoint composite
/api/v5/chart/solar-return — solar return chart
/api/v5/chart/lunar-return — lunar return chart
/api/v5/now/chart — chart for the current moment
Plus matching /chart-data/* endpoints that return JSON without SVG

That's a clean, sharp API focused on the calculations that 80% of astrology apps actually need. If your app needs Arabic parts, primary directions, dashas, BaZi, or built-in AI interpretations, you'll be writing them yourself or stitching them in from elsewhere.

Bottom line on coverage: Astrology API is wider; Astrologer API is narrower but extremely clean, and ships with SVG out of the box, which Astrology API does not.

Performance & accuracy

Accuracy. Both products are built on Swiss Ephemeris, which is itself derived from NASA JPL DE431. Planetary positions match to within 0.001 arcseconds when computed from identical inputs. There is no meaningful accuracy gap between these two providers for standard planetary work.

Where small differences appear:

House cusp algorithms. Astrology API ships 23 house systems including obscure ones (Topocentric, Alcabitius, Krusinski). Astrologer API ships ~9 systems via Kerykeion's defaults.
Sidereal ayanamsa choices. Astrology API supports a broader list of ayanamsas for sidereal calculations.
Asteroid catalog depth. Astrology API exposes more asteroids and TNOs natively; Kerykeion focuses on the core set.

Performance. Astrology API reports ~287ms average response time on its own infrastructure, with a CDN-fronted edge network. Astrologer API runs as a RapidAPI-fronted service, which adds a routing hop. Expected response time from US East Coast is 400–900ms depending on endpoint and whether SVG rendering is requested. SVG generation is the biggest variable: returning a rendered chart adds tens to hundreds of milliseconds because the SVG has to be produced server-side.

If raw speed matters — autocomplete-style transit widgets, push-notification horoscopes that need to land in under a second — Astrology API has a clear lead. If you need an SVG chart in your response and you accept a slower first response, Astrologer API is a fair trade.

Developer experience

Documentation. Astrology API ships OpenAPI specs, code samples in JavaScript, Python, Ruby, PHP, Go, and Swift, plus a dashboard with usage analytics, error logs, and rotating keys. Astrologer API has a clean README, a Swagger/OpenAPI definition, a live playground at astrologer-api-playground.kerykeion.net, and excellent inline examples in the Kerykeion library docs.

SDKs. Astrology API maintains official SDKs in five languages. Astrologer API does not currently ship official SDKs; you call it as a REST API with any HTTP client. Because the underlying library is Python, Python users can also just install Kerykeion locally — but only if their app license is AGPL-compatible.

Error handling. Both providers return structured JSON errors. RapidAPI adds its own error envelopes when quota limits or authentication issues hit, which means Astrologer API consumers have two error layers to handle: the marketplace's and the upstream's.

Onboarding speed. Astrology API: get a key, copy a sample, render a chart in under five minutes. Astrologer API: subscribe on RapidAPI, copy the X-RapidAPI-Key header, call an endpoint — also under five minutes. Both are excellent here.

When to choose Astrology API

Pick Astrology API if you need:

More than the core natal/synastry/transit calculations — Arabic parts, primary directions, profections, dashas, BaZi, harmonic charts, fixed stars, asteroids beyond the basics
Built-in AI interpretations in multiple languages, without bringing your own LLM
Sub-300ms response times for latency-sensitive UI (autocomplete, push notifications, AR overlays)
Direct USD billing without going through a marketplace
Vedic or Chinese astrology coverage in the same API surface as Western
23 house systems including the rarer ones professional astrologers ask for
Predictable per-request pricing without per-endpoint credit costs

It also wins if your team values having a single vendor, a single dashboard, and a single line item on the company card.

When to choose Astrologer API (Kerykeion)

Pick Astrologer API if you need:

Open-source roots. Kerykeion is AGPL-3.0 and active on GitHub. If your project values OSS provenance and contributes back, this matters.
SVG charts out of the box. Astrologer API returns rendered SVG natal/synastry/transit charts — no client-side rendering library required. This is genuinely useful and not something Astrology API ships today.
You're already on RapidAPI. If procurement won't add a new vendor but RapidAPI is approved, Astrologer API is a frictionless way in.
Your needs are narrow. Natal + synastry + transits + composite + returns covers the vast majority of consumer-astrology app use cases. The Astrologer API does these well.
You can self-host. If your app is AGPL-compatible (or you're shipping internal tools), you can install Kerykeion as a Python library and skip the API entirely. That's not the case with Astrology API — there is no library-only path.
Indie / hobby projects. Small audience, no need for AI interpretations or Vedic depth, and you appreciate that the project's pricing partly funds an active open-source author.

Honest note: g-battaglia maintains Kerykeion as one of the most active modern astrology open-source projects. If you ship a commercial product on top of Kerykeion via the hosted API, you're supporting that ecosystem.

Migration notes

Migrating between the two requires mapping inputs and outputs.

Inputs. Both APIs accept date, time, latitude, longitude, and timezone. Astrology API uses an explicit house_system enum (e.g., placidus, whole_sign). Kerykeion uses single-letter codes from Swiss Ephemeris (P for Placidus, W for Whole-Sign, etc.). Map your enum values during the migration.

Outputs. Astrology API returns nested JSON keyed by planet name, with degrees, retrograde flags, dignities, and house placements. Astrologer API's data-only endpoints return a similar shape but with Kerykeion's naming conventions. A small adapter layer keeps your downstream UI stable while you switch.

SVG. If you were relying on Astrologer's SVG output, you'll need a client-side chart renderer when switching to Astrology API. There are several good ones — Kerykeion's own SVG generator works standalone if your codebase is OSS-compatible, and there are MIT/BSD-licensed alternatives on npm.

Caching. Astrology API is deterministic for identical inputs and house systems. Caching is straightforward. The same is true for Astrologer's data-only endpoints. AI interpretation responses on Astrology API are deterministic per seed but vary with the underlying model version, so cache those with a model-version key.

FAQ

Is Astrologer.com (the website) the same as the Astrologer API?

No. astrologer.com is Robert Currey's astrology consultancy and the home of the Correlation Journal — a peer-reviewed publication. The Astrologer API is a separate hosted service by g-battaglia, built on Kerykeion and distributed via RapidAPI. The naming collision causes regular confusion. If you searched for an API and landed on the consultancy site, you wanted the second one.

Is Kerykeion really free to use?

The Python library itself is AGPL-3.0 — free to use, but if your application calls the library directly over a network, your full app source must be released under AGPL. Most commercial apps can't accept that, which is exactly why the hosted Astrologer API exists. Calling the hosted API does not trigger AGPL obligations; you're consuming a third-party service.

How do I know which one to start with for a hobby project?

If your hobby project is open-source and you're comfortable with Python, install Kerykeion locally — it's free and excellent. If your hobby project is a web app and you'd rather not host a Python service, both Astrology API's free tier (50 req/mo) and Astrologer API's free RapidAPI tier are reasonable starting points. Astrology API gives you slightly more headroom for AI interpretations on the free tier.

Do I lose accuracy going from Astrologer API to Astrology API or vice versa?

No, both rely on Swiss Ephemeris for planetary positions. Differences appear only in derived calculations: a few extra house systems on Astrology API, a few extra dashas, more asteroids. Core natal and transit math matches between the two providers.

Can I use both?

Yes, and some teams do. A common pattern: Astrology API for the heavy lifting (interpretations, Vedic, transits) and Astrologer API for SVG chart rendering. Hit each from your backend, cache the responses, and your users see one cohesive product.

Last verified May 10, 2026. Pricing and feature claims for Astrologer API come from kerykeion.net, the Astrologer-API GitHub README (v5), and the RapidAPI listing. Astrology API claims come from our own infrastructure; the comparison guide covers the broader market.

Astrology API vs Astrologer.com: Full Comparison (May 2026)