About

Why we built TathaAstu

Hindu calendar calculations sit underneath a great deal of software. Almost none of it can explain the dates it displays.

The problem

Hindu calendar calculations sit underneath temple apps, matrimony platforms, festival calendars, payroll, travel, publishing and now AI assistants. Yet the APIs serving them return a date and nothing else. When the date is disputed — and it is disputed often, because these are questions communities care about — there is nothing to inspect.

What we changed

We rebuilt the festival engine around shastric kala-vyapini rules operating on real tithi intervals, rather than matching whatever tithi happened to be running at sunrise. Then we made the engine show its work: every festival carries the rule, the version, the authority, the overlap in minutes, and a confidence score.

Why it matters

A date you can audit is a date you can defend. An HR department can answer an employee. A temple committee can review a schedule. A newsroom can cite a source. An AI agent can ground an answer instead of inventing one.

What we will not do

We will not publish a number we have not measured, and we will not hide a limitation to look better. The Accuracy page lists our known problems because you are going to find them eventually, and it is better that you find them from us.

History

How the platform got here

Eight milestones, in order. The interesting one is M4 — the point at which festivals stopped being a lookup table.

  1. Foundation

    Initial API surface, panchang data import across 14 cities.

  2. Auth and usage

    JWT auth, API key management, plan-based rate limiting, usage tracking.

  3. Astrology

    Birth chart, Guna Milan compatibility, PDF reports, matchmaking engine.

  4. Festival Engine V2 — core

    KalaCalculator, nine evaluators, TieBreakEngine, rule versioning, schema migration.

  5. Festival Engine V2 — cutover

    Tier A/B/C validation, shadow mode, production cutover.

  6. Platform alignment

    Tier enforcement, webhook platform, plans and billing, analytics.

  7. Security hardening

    Credentials moved to environment, secrets rotated, 152 tests at 91% coverage.

  8. Verification framework

    Execution engine, comparison policies, adapter registry, external benchmark.

A note on how we talk about accuracy

We publish our known limitations, our real latency figures, and the fact that our coverage number once went down rather than up when we measured it honestly. None of that is flattering. It is, however, the only basis on which you should trust a platform whose entire value proposition is transparency.