Indonesian developer Pijar Sukma Adiluhung says he noticed a one-day mismatch between a Hijri date shown on the Ministry of Religious Affairs (Kemenag) website and the ministry’s published calendar. Later, he says, the website stopped showing that date. He does not know why either event happened—and his account does not establish which display was wrong. The experience led him to build mabims.dev, an API intended to provide Hijri dates for Indonesia.
What happened, according to the developer
In his August 29, 2026 account, Adiluhung describes a practical problem: “If I’m an Indonesian developer and I want to display the Hijri date according to Kemenag, what do I use?” He says the date on Kemenag’s website did not match its published calendar by one day, and that the website later stopped displaying it. He also writes, “I didn’t know what exactly happened behind the scenes.”
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That distinction matters. The account reports a disagreement between two Kemenag displays, but does not document the original date or identify whether the cause was a software bug, a calculation, a data update, or something else. Nor does it establish who removed the date from the website or why. “Wrong” is the author’s framing of the mismatch, not an independently adjudicated finding about which display was correct.
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Why a Hijri date can depend on the source
A date returned by a calendar library is only as relevant as the calendar system and jurisdiction behind it. Adiluhung contrasts Kemenag’s Indonesian calendar with the Umm al-Qura calendar, which serves a different official context. He says dates can differ by a day, but his post does not establish how often that happens across APIs or libraries.
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For an application meant to show an Indonesian reference date, a generally valid Hijri conversion may not be equivalent to the locally intended date. Developers should identify the calendar source and intended jurisdiction rather than treating all Hijri-date APIs as interchangeable.
How mabims.dev is intended to work
Adiluhung says mabims.dev uses Kemenag’s official calendar as its primary source, then applies Neo MABIMS criteria as a fallback outside the range covered by that calendar. He describes the API as free, open source, and usable without an API key. Those are the project author’s claims; they have not been independently audited here.
The design reflects a useful source hierarchy: use the locally relevant official calendar where available, and make clear when a calculation-based fallback is being used. An API response should therefore be understood as a calendar date produced under its data and fallback rules—not, by itself, as an official government announcement of a month’s beginning.
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Indonesia’s 2026 Ministry of Religious Affairs regulation defines the relevant imkanurrukyat thresholds as a topocentric Moon altitude of at least 3 degrees and a geocentric Moon elongation of at least 6.4 degrees. In English translation, the regulation says the “minimum position of the hilal meets the criterion of Topocentric Moon altitude 3° (three degrees) and Geocentric Moon Elongation 6.4° (six point four degrees).” See the 2026 regulation.
Kemenag says the updated MABIMS criteria were adopted for Indonesian use beginning in 2022. MABIMS refers to the ministers of religious affairs of Brunei Darussalam, Indonesia, Malaysia, and Singapore, according to the ministry’s history of the criteria.
An API date is not the official month-start decision
The 2026 regulation describes the official determination of the starts of Ramadan, Syawal, and Zulhijah as an isbat process involving hisab (astronomical calculation) and rukyat (observation), in relation to imkanurrukyat criteria. A calendar endpoint can help software display dates, but it does not conduct that process or replace Kemenag’s official determination.
For applications where a month-start announcement has religious or operational significance, keep the API’s calendar output distinct from the government’s isbat announcement. The former is a data value from a calendar source; the latter is an official determination made through the stated procedure.
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The practical lesson for developers
- Choose a calendar source that matches the country and audience your application serves.
- Document whether dates come from a published official calendar, a calculation, or a fallback rule.
- Do not present a prepublished date as an official month-start announcement unless the relevant authority has made that determination.
- When two official displays appear to disagree, report the mismatch accurately without assuming its cause or which display was authoritative.
Adiluhung’s story is ultimately about a gap between a user-facing date and its reference calendar—and the difficulty of knowing what to trust when they conflict. Its strongest lesson is not that a particular system was proven faulty, but that date APIs should make their source, jurisdiction, and limits legible.
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