Questions we are asked most
If your question is about a specific date being wrong, the contact page explains exactly what to send us.
What is Panchang?
Panchang is the traditional Hindu calendar system that tracks five elements: Tithi (lunar day), Nakshatra (lunar mansion), Yoga (sun-moon angle combination), Karana (half-tithi), and Vara (weekday). It also includes muhurat (auspicious timings), sunrise/sunset, and festival dates.
How accurate are your calculations?
We use Swiss Ephemeris with Lahiri ayanamsa, and kala definitions following Dharmasindhu and Nirnayasindhu conventions. Verification runs in three tiers on every build: Tier A compares 7 festivals across 1950–2100 against DrikPanchang (42/42), Tier B locks an every-day hash across 8 years to catch silent drift, and Tier C replays 22 days of a production accuracy audit (26/26). The suite is 152 tests at 91% coverage. Our known limitations are published on the Accuracy page.
What is explainability?
Explainability means every API response includes reasoning — not just a result, but the derivation chain that produced it. For festivals, we show which rule was applied, which authority it came from, and the astronomical basis. This transparency is unique to TathaAstu.
What is the Festival Engine?
The Festival Engine is our derivation system that computes festival dates from first principles — astronomical positions → panchang elements → festival rules → calendar dates. It uses a multi-authority hierarchy (Kala Vyapini) with explainable outputs and versioned rules.
Do you offer a free tier?
Yes. The Free plan includes 500 requests per day with access to the Panchang and Festival APIs, and no card is required. Confidence scores and the engine version envelope are included on every plan, including Free.
Which cities do you support?
Fourteen cities across India, Nepal and Sri Lanka. Be aware that festival derivation is fully verified for New Delhi; other locations run through the same engine but have thinner cached panchang data behind them, and one location is only partially imported. This is documented on the Accuracy page. Enterprise plans can have custom cities imported and verified.
What are the rate limits?
Free: 500 req/day. Starter: 100K req/month. Pro: 1M req/month. Enterprise: unlimited. Rate limits are enforced per API key and reset according to your plan period.
How do I get started?
Create a free API key from the dashboard, then send a request with an X-API-Key header. The developer quickstart walks through four steps, ending with an explained festival response. You can also try every endpoint in the playground without an account.
Do you support Hindi or other languages?
Yes. Our API supports 50+ languages for transliterations. Tithi, nakshatra, yoga, and festival names can be returned in Hindi, Sanskrit, Tamil, Telugu, and many more languages.
What is Kala Vyapini?
Kala Vyapini is our multi-authority rule hierarchy for festival derivation. Instead of relying on a single source, we reference multiple authoritative texts and modern references, with a clear conflict-resolution chain. This ensures accurate and culturally appropriate festival dates.