This crate is part of the Rust Zmanim Project.

Zmanim Calculator

A Rust library for calculating halachic zmanim (times), following KosherJava naming and behavior. Supports no_std environments and includes an optional C FFI.

Installation

cargo add zmanim-calculator chrono

Or manually add to your Cargo.toml:

[dependencies]

zmanim-calculator = "0.1"

Usage

use chrono::{NaiveDate, Utc};
use zmanim_calculator::{
    prelude::{CalculatorConfig, Location, ZmanimCalculator},
    presets::{SUNRISE, TZAIS_MINUTES_72},
};

fn main() {
    let location = Location::new(40.7128, -74.0060, 10.0, Some(Utc)).expect("valid location");
    let date = NaiveDate::from_ymd_opt(2026, 3, 1).expect("valid date");
    let mut calc =
        ZmanimCalculator::new(location, date, CalculatorConfig::default()).expect("calculator");

    let sunrise = calc.calculate(SUNRISE).expect("sunrise");
    let tzais = calc.calculate(TZAIS_MINUTES_72).expect("tzais");

    println!("Sunrise (UTC): {sunrise}");
    println!("Tzais 72 (UTC): {tzais}");
}

If you omit a timezone, calculations near the anti-meridian (|longitude| > 150) will fail. Kiddush Levana and Molad calculations require a timezone as well.

Feature Flags

• std — Enables standard library support
• defmt — Enables defmt formatting/logging for embedded targets
• c — Enables the C FFI surface and header generation tooling (std is enabled automatically)

C API

Pre-built libraries and the C header are available on the GitHub Releases page for Linux, macOS, and Windows.

Generate the header:

cargo run --features c --bin build_c_headers

Build the C-callable library:

cargo build --release --features c

The header is written to bindings/c/zmanim_calendar.h.

See example-c-project/ for a complete usage example.

Compatibility

The API aims to follow KosherJava naming and behavior where possible. For background and broader algorithm documentation, see the KosherJava documentation.

License

Licensed under LGPL-2.1. See LICENSE for details.