Author Archives: mradwin

Hebcal.com now offers an experimental REST API for determining for a given location if the date and time has a melacha (work) prohibition. This API can be used by home automation systems or other applications that wish to change functionality when Shabbat or yontiff begins or ends.

Although there are many opinions on the time of tzais, for simplicity this function uses solar depression of 8.5 degrees. More about Havdalah.

Note that this is a web API with the same functionality as the isAssurBemlacha API provided by the JavaScript @hebcal/core package. If you’re building a JavaScript application, consider using the native JS library instead of web APIs for a faster user experience.

The basic URL format is as follows:

https://www.hebcal.com/zmanim?cfg=json&im=1&geonameid=3448439&dt=2025-06-21T20:08:10Z

Parameters and their meanings

• cfg=json – output JSON. Required
• im=1 – enable issur melacha mode. Required
• Location: Specify the desired location using GeoNames.org numeric ID, United States ZIP code, or latitude/longitude. This page also describes how to enable/disable the optional elevation for sunset calculation.
• dt=YYYY-MM-DDTHH:mm:ss.sssZ – optionally specify an exact time to check
  • If specified, the date-time must follow the ISO 8601 Date time string format
    • Note Z is the timezone offset, which can either be the literal character Z (indicating UTC), or + or - followed by HH:mm, the offset in hours and minutes from UTC. If using a UTC positive time zone offset, take care to url-encode the + as %2b
    • If the date-time does not end with a time zone offset, the time will be interpreted as the local timezone of the location specified
  • If this optional date-time parameter is absent, the API will use the current local time at the location

Example output

{
  "date": "2025-06-23T04:52:52.475Z",
  "version": "5.10.0-3.4.1",
  "location": {
    "title": "São Paulo, Brazil",
    "city": "São Paulo",
    "tzid": "America/Sao_Paulo",
    "latitude": -23.5475,
    "longitude": -46.63611,
    "cc": "BR",
    "country": "Brazil",
    "admin1": "Sao Paulo",
    "asciiname": "Sao Paulo",
    "geo": "geoname",
    "geonameid": 3448439
  },
  "status": {
    "localTime": "2025-06-21T17:08:10-03:00",
    "isAssurBemlacha": true
  }
}

Usage notes

As with all Hebcal.com REST APIs:

• Both HTTP and HTTPS (HTTP/2) are supported. Although most of the Web has moved to HTTPS, if you wish to reduce CPU overhead on your client you may continue to use plain (port 80) HTTP for API requests
• We encourage HTTP caching proxies. Proper Cache-Control and Expires are generated in the response
• We support both gzip and br (brotli) compression; set the appropriate Accept-Encoding header in your request to enable
• We support HTTP Keep-Alive for multiple requests

Licensing

Content generated by the Hebcal.com web APIs is licensed under a Creative Commons Attribution 4.0 International License. This means that you can use you are free to copy and redistribute the material in any medium or format as long as you give appropriate credit to Hebcal.com.

Hebcal.com Web APIs allow the developer to specify a location using one of four options.

Location is used to estimate candle-lighting, Havdalah, fast start/end times, and other zmanim (halachic times). All of these times are derived from a solar position calculation, which are approximated from a location (latitude, longitude) and day of year.

Option 1: GeoNames

To specify a location using a GeoNames numeric ID, use the geonameid parameter, e.g. geonameid=3448439

The GeoNames geographical database covers all countries and contains over eleven million placenames that are available for download free of charge. Hebcal.com supports a subset of the full database: approximately 150,000 world cities with a population of 1,000 or more.

For a complete list of IDs that the Hebcal.com web APIs accept, download the cities1000.zip from https://download.geonames.org/export/dump/ and consider only rows with a type of P (inhabited place). Hebcal refreshes this database approximately once per year.

Option 2: United States ZIP code

To specify a location using a 5-digit ZIP code in the US, use the zip parameter, e.g. zip=90210

If a longer ZIP code (for example a ZIP+4) is specified, only the first 5 digits will be considered.

Hebcal licenses a commercial ZIP code database and we refresh this database approximately once per year.

Option 3: Latitude and Longitude

To specify a location using a latitude and longitude and timezone, use 3 required parameters and one optional parameter.

1. latitude=[-90.0 to 90.0] – latitude in decimal format (e.g. 31.76904 or -23.5475)
2. longitude=[-180.0 to 180.0] – longitude decimal format (e.g. 35.21633 or -46.63611)
3. tzid=TimezoneIdentifier. See List of tz database time zones

Be sure to use the “TZ database name” such as America/New_York or Europe/Paris, not a UTC offset.

An optional parameter elev=[1-9000] may also be used to specify the elevation in meters. This parameter will be ignored unless ue=on, see below for further details.

Option 4: Legacy city identifier (deprecated)

To specify a location using one of ~400 Hebcal legacy city identifiers, use the city parameter, e.g. city=GB-London

You must use one of the legacy city identifiers. Case insensitive. This approach is generally deprecated, as we now recommend using geonameid instead.

Elevation

All of the above options can optionally utilize an elevation for sunset calculation. To enable elevation, specify ue=on (default off).

If on, use elevation to affect the calculation of all sunrise/sunset based zmanim. Note: there are some zmanim such as degree-based zmanim that are driven by the amount of light in the sky and are not impacted by elevation. These zmanim intentionally do not support elevation adjustment

Accuracy

For more information on the calculation engine, see How accurate are candle lighting times?