Ely Jacobi — Elyahu41 on GitHub
Mobile software that has to be exactly right.
I'm an Android and iOS engineer. Most of what I build calculates something down to the second, halachic times derived from the sun's position, or the exact pixel a bot needs to tap and I've come to like software that has to be correct, not just working.
About
I build mobile apps — mostly Android, increasingly iOS — with Jewish calendar and zmanim calculation at the center of a lot of it. That means turning astronomical formulas — sun altitude, degrees below the horizon, seasonal changes — into something that runs reliably on a phone, a watch face, or a home-screen widget.
The rest of my time goes to smaller, sharper problems: a Gemini-powered app that reads a plate of food and estimates its calories, computer-vision bots that read a game board and solve it deterministically, and whatever CI/CD pipeline needs fixing that week.
I ship through GitHub Actions and Firebase Hosting, and I'd rather track down a subtle timezone bug than route around one.
Mobile
AI & backend
Tools & pipelines
Featured work
A few of the projects I keep coming back to.
R' Ovadiah Yosef Calendar
A Jewish calendar app for phone and watch, with live Wear OS complications and full-screen zmanim alarms that respect Android 14's background-launch limits. Dual-provider location arbitration picks the best fix within a timeout instead of trusting whichever provider answers first.
View repositoryRabbeinu Tam (iOS)
A SwiftUI app that calculates Tzet — nightfall — under the Rabbeinu Tam opinion, with several sub-opinion methods to pick from. Built on KosherSwift, with a home-screen widget and local notifications timed to the calculated moment.
View repositoryKosherSwift
A ground-up Swift port of the KosherJava zmanim library, so iOS apps can calculate halachic times without going near a JVM. It's the project of mine that other developers actually depend on.
Zmanim Map
A standalone Android app, based on koshermap.com, built for kosher phones that don't have Google Play Services. Three interchangeable map providers, offline timezone resolution, and fourteen zmanim in a persistent bottom sheet, all wired through a single location resolver.
How Many Calories
Point a camera at a plate, get a calorie estimate back. A Material Design 3 Android app backed by Gemini through a small Node.js proxy, with a daily tracker and a home-screen widget.
Woodoku Blast Bot
A fully deterministic bot for a block-puzzle mobile game. OpenCV reads the board by color, a brute-force solver picks the move, and pixel-calibrated anchors place every drag exactly where it needs to go — no guessing, no vision-based correction after the fact.
View repositoryVoice-Activated Assistant
An early exploration into practical AI: a customizable, voice-driven personal assistant built in Python.
View repositoryAlso in the mix
Ports, forks, and one very large voxel game.
KosherJava (zmanim)
The Java zmanim library that started it all for this whole family of apps. I maintain a fork alongside the Swift and Cocoa ports.
View repositoryKosherCocoa
An Objective-C zmanim port for the Apple ecosystem — the predecessor to KosherSwift.
View repositoryTerasology
A Java, Minecraft-like open-world voxel game. I've contributed to it as an outside collaborator.