An engine and a versioned book of rulings for the Hindu calendar. Every date arrives with the sky it was read from, the rule that decided it, and the authorities that say otherwise.
Budhavāra · Wed 11 November 2026 · 08:23:42 UTC+05:30
Kārtika Śukla Dvitīyā
until 15:54 · nakṣatra Anurādhā · yoga Atigaṇḍa · karaṇa Kaulava
Sun 21.3° above ESE
4 ghaṭī 24 pala since sunrise
Samrāṭ yantra built for 23°11′ N
The problem, drawn
The new-moon tithi of Diwali 2025 ended at 12:25 UTC on 21 October. The rule for Lakṣmī Pūjā asks one question of each place: was it still present after sunset? Jersey City had kept the night before. Delhi had ten minutes of it. Sydney had the whole evening.
The rule that reads it
Lakṣmī Pūjā falls on the evening when Amāvasyā prevails during pradoṣa, the two muhūrtas after sunset. If both qualify the text is silent: the longer is ruled, as a boundary. CRC 1955, General Rules for Religious Festivals, as profile pac-rp@2026.1.
Principle 1
Fact · AngaInterval
Amāvasyā
20 Oct 2025 10:15:27 → 21 Oct 2025 12:25:10 UTC
The root of a monotonic function, bracketed and solved to the second under a declared method. It is the same instant in every city and for every tradition. Nobody is asked for an opinion.
Ruling · Ruling
Lakṣmī Pūjā
Monday 20 October, Delhi
A rule, a tradition and a profile applied to the facts, with every step written out so that a person or an agent can quote it. Another authority may rule otherwise. When one does, it is listed beside the answer, never under it.
Machine surfaces
One canonical address per place and day, served as a page, JSON, Markdown or a calendar file from the same resource. An MCP server with five tools. No key, no account, and the method echoed in every response.
| REST | Keyless. Open CORS, no account. | /v1/day/{place}/{date} |
| Negotiated page | HTML, JSON, Markdown, ICS | /{place}/{date} |
| MCP | Streamable HTTP, five tools | /mcp |
| Calendar feeds | Festivals, ekādaśī, tithi | /{place}/calendar/festivals.ics |
| Manifests | Profiles and the ruleset, as data | /v1/methods · rules |
| Descriptions | OpenAPI 3.1, and llms.txt for a model | /openapi.json · /llms.txt |
| Packages | Engine, rules, places. Not yet published. | soon |
$ curl -H 'Accept: application/json' \ https://ahargana.org/delhi/festivals/2025/diwali-lakshmi-puja { "id": "/delhi/festivals/2025", "place": { "id": "1273294", "slug": "delhi", "name": "Delhi", "region": "India", "country": "IN", "lat": 28.65195, "lon": 77.23149, "elevation_m": 227, "tz": "Asia/Kolkata" }, "year": 2025, "tradition": "smarta", "method": "pac-rp@2026.1", "ruleset": "2026.3-draft", "rulings": [ { "id": "/delhi/festivals/2025/diwali-lakshmi-puja", "festival": "diwali-lakshmi-puja", "name": "Lakṣmī Pūjā", "tradition": "smarta", "place": "1273294", "year": 2025, "local_date": "2025-10-20", "confidence": "boundary", "boundary_reasons": [ "tie-break-unstated" ], "boundary_margin_s": 601, "anga": { "type": "tithi", "index": 29, "key": "amavasya", "name": "Amāvasyā", "start": { "local": "2025-10-20T15:45:27+05:30", "utc": "2025-10-20T10:15:27Z", "ms": 1760955327081.2507 }, "end": { "local": "2025-10-21T17:55:10+05:30", "utc": "2025-10-21T12:25:10Z", "ms": 1761049510434.19 }, "month": { "amanta": 6, "purnimanta": 7, "adhika": false, "amanta_name": "Āśvina", "purnimanta_name": "Kārtika" } }, "span": { "of": "tithi", "start": { "local": "2025-10-20T15:45:27+05:30", "utc": "2025-10-20T10:15:27Z", "ms": 1760955327081.2507 }, "end": { "local": "2025-10-21T17:55:10+05:30", "utc": "2025-10-21T12:25:10Z", "ms": 1761049510434.19 } }, "kaala": "pradosha", "days": [ { "local_date": "2025-10-20", "window": { "start": { "local": "2025-10-20T17:46:08+05:30", "utc": "2025-10-20T12:16:08Z", "ms": 1760962567859.264 }, "end": { "local": "2025-10-20T19:27:26+05:30", "utc": "2025-10-20T13:57:26Z", "ms": 1760968645624.3972 } }, "covered_min": 101, "window_min": 101, "qualifies": true }, { "local_date": "2025-10-21", "window": { "start": { "local": "2025-10-21T17:45:10+05:30", "utc": "2025-10-21T12:15:10Z", "ms": 1761048909912.453 }, "end": { "local": "2025-10-21T19:26:41+05:30", "utc": "2025-10-21T13:56:41Z", "ms": 1761055000579.7822 } }, "covered_min": 10, "window_min": 102, "qualifies": true } ], "decided_by": "greater-coverage", "explanation": [ { "step": "anga", "text": "Amāvasyā runs from 15:45 on Mon 20 Oct to 17:55 on Tue 21 Oct.", "fact": "2025-10-20T10:15:27Z → 2025-10-21T12:25:10Z" }, { "step": "kaala", "text": "Pradoṣa is 2 muhūrtas after sunset: 17:46–19:27 on the 20th, 17:45–19:27 on the 21st.", "fact": "pradosha: night-muhurta-1-2 · sunrise and sunset: upper limb, 31′ + 16′" }, { "step": "rule", "text": "Amāvasyā must be present during pradoṣa. It covers 101 of 101 minutes on the 20th and 10 of 102 on the 21st.", "fact": "Calendar Reform Committee 1955, General Rules for Religious Festivals, p. 104" }, { "step": "tie_break", "text": "Both evenings qualify and the rule marks neither. The one covered longer is ruled, as a boundary.", "fact": "priority: unstated → greater-coverage · margin 601 s" }, { "step": "ruling", "text": "Lakṣmī Pūjā, Delhi, 2025: Monday 20 October.", "fact": "confidence: boundary (tie-break-unstated)" } ], "rule": { "kind": "lunar", "id": "diwali-lakshmi-puja", "references": [ { "text": "Calendar Reform Committee 1955, General Rules for Religious Festivals", "locator": "p. 104", "url": "https://archive.org/details/calendar_reform_comittee_report", "quote": "K 30 Kali puja (nisithavyapini), Dipavali or Diwali (pradosa), Mahalaksmipuja (pradosa)" } ], "kaala": "pradosha", "priority": "unstated", "when_absent": "unstated" }, "alternatives": [ { "kind": "profile", "profile": "classical@2026.1", "local_date": "2025-10-20", "confidence": "boundary" }, { "kind": "profile", "profile": "compat-drikpanchang@2026.1", "local_date": "2025-10-20", "confidence": "boundary" }, { "kind": "institution", "institution": { "id": "nse", "name": "National Stock Exchange" }, "local_dates": [ "2025-10-21" ], "statement": "Muhūrat trading, circular of 22 Sep 2025", "source_url": "https://www.business-standard.com/markets/news/nse-to-hold-one-hour-diwali-muhurat-trading-session-on-october-21-125092200907_1.html", "captured_at": "2026-09-11" }, { "kind": "institution", "institution": { "id": "google-calendar-in", "name": "Google Calendar" }, "local_dates": [ "2025-10-20" ], "statement": "Holidays in India feed", "source_url": "https://calendar.google.com/calendar/ical/en.indian%23holiday%40group.v.calendar.google.com/public/basic.ics", "captured_at": "2026-09-11" }, { "kind": "institution", "institution": { "id": "apple-icloud-in", "name": "Apple iCloud" }, "local_dates": [ "2025-10-20", "2025-10-21" ], "statement": "India Holidays feed, listed twice", "source_url": "https://calendars.icloud.com/holidays/in_en-in.ics", "captured_at": "2026-09-11" }, { "kind": "institution", "institution": { "id": "rashtriya-panchang", "name": "Rashtriya Panchang" }, "local_dates": [ "2025-10-20" ], "statement": "Principal festivals, 2025-26", "source_url": "https://packolkata.imd.gov.in/rashtriya-panchang-english.php", "captured_at": "2026-11-10" } ], "quote": "In Delhi, Lakṣmī Pūjā (Diwali) 2025 falls on Monday 20 October. Amāvasyā runs from 15:45 on Mon 20 Oct to 17:55 on Tue 21 Oct and covers all of pradoṣa that evening. It also reaches the next evening for 10 minutes; the rule does not say which to take, and the one covered longer is ruled: treat the date as contested. National Stock Exchange recorded 21 October (Muhūrat trading, circular of 22 Sep 2025). Apple iCloud recorded 20 October and 21 October (India Holidays feed, listed twice).", "cite": "https://ahargana.org/delhi/festivals/2025/diwali-lakshmi-puja", "method": "pac-rp@2026.1", "engine": { "version": "0.1.0", "ruleset": "2026.3-draft", "kernel": "de440-1900-2100", "kernel_sha256": "7eef444f9e5bd8786b8b5b72e775ecc376991b953a6246ec7a49d2c37434ea74", "tzdata": "2026f" } } ], "engine": { "version": "0.1.0", "ruleset": "2026.3-draft", "kernel": "de440-1900-2100", "kernel_sha256": "7eef444f9e5bd8786b8b5b72e775ecc376991b953a6246ec7a49d2c37434ea74", "tzdata": "2026f" } }
Same resource, same bytes for the same inputs. ETag is the hash of engine, ruleset, kernel and request.
Conformance
Each profile is measured against the people who publish almanacs: the Positional Astronomy Centre, the Rashtriya Panchang, station sunrise tables, ISKCON’s calendar. Where an authority and the engine part ways, the difference stays in the table as a fixture.
Measured 10 November 2026 · engine 0.1.0
53 of 53 PAC values reproduced
The widest difference is 30 s, against a budget of sixty for print. See every row
| Quantity | Budget | Checked against | Tier |
|---|---|---|---|
| Sun and Moon longitude | ≤ 0.05″ · 0.0070″ | JPL Horizons, 1900–2100, 120 instants | oracle |
| Tithi and karaṇa boundary | ≤ 60 s print · 30 s | PAC daily page, 53 printed end-times | A |
| Nakṣatra and yoga boundary | ≤ 60 s print | the same PAC rows | A |
| Saṅkrānti instant | ≤ 30 s · 1 s | Swiss Ephemeris, Lahiri mode 1 | oracle |
| Sunrise and sunset | ≤ 1 s · 0.1 s | Swiss Ephemeris, same model; one PAC station | D |
| Festival dates, pac-rp | 100% · 162 of 181 | Rashtriya Panchang lists, 2022–27 | C |
| Vaiṣṇava dates, iskcon-gcal | 100% | GCal 11, ten cities | C |
A solid mark is measured in the last run, with the widest difference beside its budget. A hatched mark is measured and short of its budget. A ring is a budget whose fixtures are not built yet. A divergence, once found, stays in the table as a fixture and is never patched.