Zmanim and Hebrew Dates
Chatbots get Hebrew dates and zmanim wrong; the tools members use instead (Chabad.org, Hebcal and its MCP, zman.ms5.uk, member-built Shabbos-times sites) and the checks to run before any time goes out.
On this page
Do not ask a chatbot what time candle lighting is, or what Hebrew date someone was born on. Members tested it repeatedly in 2026 and the answers were unreliable. When a member asked in August 2026 how much GPT can be trusted to convert English dates to Hebrew ones, the reply was "Not very." Models are weak at date arithmetic even when they search the web.
The fix is to have the AI use a tool that calculates, and then to check the result against a source you trust before it goes to your community. Which zman to follow, and when Shabbos begins and ends where you live, are questions for your rav; nothing on this page is a psak.
Converting Hebrew dates
One date or a few. Hebcal's converter works both ways. berel.me's multi-date converter takes a pasted list and has a "past sunset?" option.
Inside Claude or ChatGPT. Hebcal runs an experimental MCP server at https://www.hebcal.com/mcp (Hebcal's announcement, July 2025). Add it as a custom connector and the assistant can call Hebcal instead of guessing. On 2026-10-21 it offered these tools: Gregorian to Hebrew and back, yahrzeit dates (with an after-sunset setting), the weekly parsha, the year's Yom Tov dates, Daf Yomi, and Shabbos and Yom Tov candle-lighting and havdalah times for a location. It does not give daily zmanim such as sof zman Shema. How to add a connector: MCP and Connectors.
A whole spreadsheet. For a list of birthdays or yahrzeits, have the AI write a small script instead of converting the dates itself. In July 2026 a member shared this approach with the free Python library convertdate and called it "finally something that works":
I am uploading a spreadsheet with a column of English birth dates. Write a
Python script that uses the convertdate library (hebrew.from_gregorian) to
add a column with the Hebrew date, written as day, month name and year.
There is also a column "after_shkiah" (yes/no). If it says yes, use the
next day's Hebrew date. If that column is empty, leave the Hebrew date
blank and mark the row "check". Run the script and give me the new file.
Do not convert any date yourself without the script.
The after-sunset column matters. Someone born after shkiah has the next Hebrew date, and the AI cannot know that unless your list records it. A shliach whose agent sent "birthdays this week" from Salesforce ran into exactly this in August 2026, because the Hebrew birthdays were never stored.
Hebcal notes that its results for the year 1752 and earlier are inaccurate, so historical dates need another source.
Where to get zmanim
| Source | What it is | Notes |
|---|---|---|
| Chabad.org Zmanim | Daily times for a city, ZIP code or exact coordinates | Settings for how many minutes before sunset to light and how Shabbos ends; a printable monthly chart and an RSS feed. |
| zman.ms5.uk | Chabad.org zmanim for any address, postcode or your current location | Community-built, July 2026. Also an MCP server at https://zman.ms5.uk/MCP with tools for daily, weekly and monthly zmanim, Shabbos times, the parsha, and a share or embed link. Step-by-step use: guide. |
| Hebcal zmanim API | Zmanim as data, for developers | Includes the Baal HaTanya times (alos, sof zman Shema and Tefillah, mincha gedola and ketana, plag, tzeis). Licensed CC BY 4.0, which asks you to credit Hebcal. |
| MyZmanim | Zmanim lookup for anywhere in the world | A member used it for a yearly chart (August 2026). |
In August 2026 a member who compared them reported that Hebcal's Baal HaTanya times came within about a minute of Chabad.org's. That is one person's comparison, not a certification.
For people building their own tools:
- @hebcal/core, Hebcal's JavaScript library, which Hebcal recommends over calling its web API from an app.
- KosherZmanim, a TypeScript version of the KosherJava zmanim library (LGPL license). Members' GabAI agents use it to work out daily zmanim offline (August 2026).
- chabad-org-zmanim, a community-built, MIT-licensed package that fetches Chabad.org's times for a location. It runs on a server, not in the browser.
Shabbos-times tools members built
All loaded on 2026-10-21.
- Shabbat.city: candle lighting and havdalah for several cities at once, converted to your time zone. Useful before a trip; it has fewer cities than Chabad.org.
- ZmanimGraphics: designs a weekly Shabbos and Yom Tov graphic with the times and emails it out automatically; free to start.
- Toronto Shabbos Times (App Store page) and berel.me's Candle Lighting Display, single screens showing this week's times.
- Shabbat Siren: a free iPhone and Android app that sounds a siren on your phone before Shabbos.
- Sjabbat Tijden: times by zone for the Netherlands. The shliach who built it said standard city times did not match how his community keeps Shabbos.
- berel.me's Our days: upcoming Chabad yomei d'pagra with a countdown to shkiah where you are.
- CountOmer reminds you to count after tzeis, and the Talking Siddur uses your location for zmanim.
Checks before a time goes out
- A minute or two is normal; more is a warning. Hebcal itself says differences of 1 to 2 minutes between sources are expected. Its list of reasons: 18 versus 20 minutes before sunset for candle lighting, different calculation engines, the exact coordinates used (a ZIP code is treated as its center point), rounding, the method used for havdalah, and elevation, which can move sunset by up to about 7 minutes in high cities.
- Check the location. Make sure the tool used the place you meant, especially for visitors, travel, or a phone's guessed location.
- Check the time zone. A countdown page shared in August 2026 had a time-zone bug that was caught the same day; it now warns users not to rely on it.
- Use the local calendar where there is one. Some communities publish their own times, such as a set time for the end of Shabbos. A member building an agent for Montreal in August 2026 had to program that city's custom separately. Follow your community's calendar and your rav.
- Draft from a source, not from memory. When a shliach shared a WhatsApp-ready Shabbos schedule in August 2026, others reminded him to double-check shkiah and tzeis; his times had come from a Chabad.org PDF, which is the right starting point.
- Do not copy an AI's halachic advice. In August 2026 an agent's tips on candle lighting and nightfall were generic and partly questionable.
A prompt for the weekly message:
Here are this week's times for [city], copied from Chabad.org:
[paste]. Write a short WhatsApp message with candle lighting, shkiah and
the time Shabbos ends. Use exactly these times. Do not calculate, round
or change any time. If a time I need is missing, write [MISSING] instead.
Then read the message against the source before you send it.
Agents and Shabbos
Members who run personal agents add Shabbos and Yom Tov gates so the agent sends nothing during those hours, using a schedule calculated in advance. That is a technical safeguard; whether and how an agent may run on Shabbos is discussed on AI and Shabbos. Ask your rav.