skills-il/idf-date-converter

IDF Date Converter

Instructions

Step 1: Identify the Request

| Request | Action | |---------|--------| | Convert specific date | Gregorian to Hebrew or Hebrew to Gregorian conversion | | When is holiday X? | Look up holiday in Hebrew calendar | | Format for document | Dual date string in Hebrew + Gregorian | | Business days | Count excluding Shabbat + holidays | | Shabbat times | Candle lighting / havdalah for city |

Step 2: Date Conversion

Use Python conversion:

# Using pyluach library
from pyluach import dates, hebrewcal

# Gregorian to Hebrew
greg_date = dates.GregorianDate(2026, 2, 24)
heb_date = greg_date.to_heb()
print(f"{heb_date.day} {heb_date.month_name()} {heb_date.year}")

# Hebrew to Gregorian (always verify the resulting date by round-tripping)
heb_date = dates.HebrewDate(5786, 11, 15)  # 15 Shvat 5786 (Tu B'Shvat) — pyluach numbers months starting at Nisan=1, so Shvat=11
greg_date = heb_date.to_greg()
print(f"{greg_date.day}/{greg_date.month}/{greg_date.year}")

Step 3: Hebrew Numeral Formatting

Hebrew dates use gematria (letter-number system):

• Units: alef=1, bet=2, gimel=3, ... tet=9
• Tens: yod=10, kaf=20, lamed=30, ... tzadi=90
• Hundreds: kuf=100, resh=200, shin=300, tav=400
• Special: 15 = tet-vav (not yod-heh), 16 = tet-zayin (not yod-vav)
• Year: Omit thousands (5786 written as tav-shin-peh-vav = 786)

Step 4: Dual Date Formatting

For Israeli documents:

24 February 2026 / 7 Adar 5786

(5786 is a regular Hebrew year, not a leap year, so there is only one Adar — no Adar I / Adar II. Always run pyluach to confirm a dual-date string before printing it.)

Step 5: Israeli Business Days

Israeli business week: Sunday through Thursday (some work half-day Friday) Non-working days:

• Every Shabbat (Friday sunset to Saturday sunset)
• All major holidays (see holiday table)
• Election days (when applicable)

def is_israeli_business_day(greg_date):
    """Check if a date is an Israeli business day."""
    # Saturday = 5 in Python's weekday() (0=Monday)
    if greg_date.weekday() == 5:  # Saturday
        return False
    # Check if it's a holiday
    heb = dates.GregorianDate(greg_date.year, greg_date.month, greg_date.day).to_heb()
    # Check against holiday list
    return not is_israeli_holiday(heb)

Israeli Holidays and Fast Days, Gregorian projection for 2026

All projections are calendar-year 2026. Where a Hebrew month spans two Hebrew years (Tishrei rolls into the next Hebrew year), the row gives the Hebrew year that the holiday actually falls in.

| Holiday / Fast | Hebrew Date | Gregorian 2026 (approx) | Hebrew Year | |----------------|-------------|-------------------------|-------------| | Tu B'Shvat | 15 Shvat | Feb 2 | 5786 | | Fast of Esther (Ta'anit Esther) | 13 Adar | Mar 2 | 5786 | | Purim | 14 Adar | Mar 3 | 5786 | | Shushan Purim | 15 Adar | Mar 4 | 5786 | | Pesach | 15-21 Nisan | Apr 2-8 | 5786 | | Yom HaShoah | 27 Nisan | Apr 14 | 5786 | | Yom HaZikaron | 4 Iyar | Apr 21 | 5786 | | Yom HaAtzmaut | 5 Iyar | Apr 22 | 5786 | | Lag BaOmer | 18 Iyar | May 5 | 5786 | | Shavuot | 6 Sivan | May 22 | 5786 | | Fast of 17 Tammuz (Shiv'a Asar B'Tammuz) | 17 Tammuz | Jul 3 | 5786 | | Tisha B'Av (9 Av) | 9 Av | Jul 24 | 5786 | | Rosh Hashana | 1-2 Tishrei | Sep 12-13 | 5787 | | Fast of Gedaliah (Tzom Gedaliah) | 3 Tishrei | Sep 14 | 5787 | | Yom Kippur | 10 Tishrei | Sep 21 | 5787 | | Sukkot | 15-21 Tishrei | Sep 26 - Oct 2 | 5787 | | Simchat Torah | 22 Tishrei | Oct 3 | 5787 | | Chanukah (5787) | 25 Kislev - 2 Tevet | Dec 5-12, 2026 | 5787 | | Fast of 10 Tevet (Asarah B'Tevet) | 10 Tevet | Dec 20 | 5787 |

Note on Chanukah: the 5787 occurrence begins on the evening of 4 Dec 2026 (kindling the first candle) and the first full Gregorian day is 5 Dec 2026 (25 Kislev). It ends 12 Dec 2026 (2 Tevet). The table shows the 5787 occurrence because that is the one that lands in calendar year 2026.

Always verify these dates with pyluach before using them in production. The corrected dates above were regenerated in v2.0.0 after the initial 2026 projection table shipped with off-by-one errors on roughly half the entries.

Yom HaZikaron / Yom HaAtzmaut displacement rules

The Knesset legislated displacement of Yom HaZikaron and Yom HaAtzmaut to avoid Shabbat desecration. Apply these rules before printing dates:

• If 5 Iyar falls on Friday or Saturday, Yom HaAtzmaut moves earlier to Thursday (4 Iyar or 3 Iyar). Yom HaZikaron moves with it.
• If 5 Iyar falls on Monday, Yom HaAtzmaut moves later to Tuesday (6 Iyar) so Yom HaZikaron does not start on Saturday night ceremonies that border Shabbat.
• If 5 Iyar falls on Sunday, Tuesday, or Wednesday, no displacement.
• Yom HaShoah (27 Nisan) is similarly displaced: if it falls on Friday it moves to Thursday (26 Nisan); if it falls on Sunday it moves to Monday (28 Nisan).

In 2026, 5 Iyar falls on Wednesday (Apr 22), so no displacement. Always re-check via pyluach or hebcal for other years.

Examples

Example 1: Simple Conversion

User says: "What's today's Hebrew date?" Result: "24 February 2026 = 26 Adar I 5786"

Example 2: Holiday Lookup

User says: "When is Pesach 2026?" Result: "Pesach begins evening of April 1, 2026 (15 Nisan 5786). First seder: April 2. Last day in Israel: April 8."

Example 3: Business Days

User says: "How many business days between March 1 and March 31, 2026?" Result: Count excluding Shabbatot, noting if any holidays fall in the range (Purim on March 3, Shushan Purim on March 4).

Bundled Resources

Scripts

• scripts/convert_date.py , Converts between Hebrew and Gregorian calendars, formats dual dates for Israeli documents, lists Israeli holidays for any year, and counts Israeli business days between date ranges (excluding Shabbatot and holidays). Requires pyluach library. Run: python scripts/convert_date.py --help

References

• references/hebrew-calendar-reference.md , Complete Hebrew calendar reference covering month names and variable lengths, the 19-year Metonic leap year cycle, gematria (Hebrew numeral) conversion table with special cases, Israeli holiday calendar with work-off days versus partial-closure days, and recommended Python libraries (pyluach, hebcal). Consult when handling leap year edge cases, formatting Hebrew numerals, or determining which holidays affect business day calculations.

Gotchas

• Hebrew calendar dates have variable month lengths (29 or 30 days) and leap years add an entire month (Adar II). Agents may assume fixed month lengths or Gregorian leap year rules.
• Israeli official documents use Hebrew dates (e.g., "כ"ה באדר תשפ"ו") while business documents use Gregorian DD/MM/YYYY. Agents may not know which format to use for which context.
• Jewish holidays move relative to the Gregorian calendar each year. Agents with static training data may cite incorrect dates for Rosh Hashana, Pesach, etc. in the current year.
• The Hebrew year starts in Tishrei (September/October), not January. Agents may miscalculate Hebrew year boundaries when converting dates near the Gregorian new year.
• Yom HaZikaron, Yom HaAtzmaut, and Yom HaShoah are subject to legislated day-of-week displacement to avoid Shabbat conflicts. Static lookup tables that hard-code "5 Iyar" without checking the day of week will print wrong dates roughly half the time. Always run the displacement rules above.
• Chanukah usually straddles two Gregorian years (late Dec into early Jan). When labeling a Gregorian year column, pick the Hebrew year whose 25 Kislev actually lands inside that Gregorian year. Mixing 5786 and 5787 dates in the same row is a common mistake.

Troubleshooting

Error: "Incorrect Hebrew date"

Cause: Hebrew months vary in length; leap year months confusing Solution: Verify with hebcal.com. Adar I/II only exist in leap years. Current year (5786) leap status affects dates.