Jaanus Siim, Developer in Tallinn, Estonia
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Jaanus Siim

Verified Expert  in Engineering

Software Developer

Tallinn, Estonia
Toptal Member Since
April 18, 2015

Jaanus is a highly skilled software developer with a passion for mobile development. In recent years, he has focused on iOS development, but he also has extensive experience with Android and J2ME platforms. Jaanus is a great communicator and enjoys working in diverse environments.



Preferred Environment

Swift, iOS

The most amazing...

...things I've coded are J2ME games on feature phones. Squeezing every part of code and resources to fit the application into 64KB jars was special.

Work Experience

Freelance iOS Developer

2012 - PRESENT
Coodly OÜ
  • Led the development of taxi ordering app Taxify, currently taking off in Europe.
  • Led the development of Taxify companion app Taxify Driver.
  • Led the development of the WeAreColony iPad app to watch indie movies.
  • Created multiple iPad quiz apps used in local bars and shopping centers.
  • Led the development of Speed Camera Tracker showing useful info for drivers in Australia.
  • Built multiple in-house apps to play around with new technologies like Swift and SpriteKit.
Technologies: iOS

Senior iOS Developer

2013 - 2014
Mooncascade OÜ
  • Led the development of the TrasnferWise iOS client. Defined app architecture and network communication with caching.
  • Rewrote the parku app (v3) targeting iOS 7 and up.
  • Led the development of KFC Heartbeat, a social app based on Glassboard and used internally by KFC.
  • Fixed bugs and improved functionality for the CarDelMar car rental app.
  • Developed a simple utility calculator for the golden ratio.
Technologies: iOS, Objective-C, Core Data

Senior J2ME and iOS Developer

2009 - 2012
MobiSolutions AS
  • Led the UI rewrite of Skype J2ME.
  • Helped intermittently on Skype's Android version.
  • Led the development of a marine navigation iOS app built on top of a C++ library provided by the client.
  • Led the developmet to extend Touchnote iOS app's functionality. First extended image editing capabilities and later did partial UI rewrite for universal app.
  • Led the development of Lifecake iOS app. Scrapbook for memories of kids growing up. Notes, photos an videos that can be shared with family.
  • Led the development of a local parking iOS app.
Technologies: iOS

Senior Java Developer

2008 - 2009
Nutiteq OÜ
  • Led the development of a mapping SDK that could be used on any platform supporting Java (J2ME, Android, BlackBerry).
  • Extended the functionality of the mapping application written in J2ME.
Technologies: Mobile App Development


A platform for real-world location-based games with support for different game types. It is used by event companies, outdoor companies, schools, and others who need to create cool location-based games fast.

Coming in, I originally moved Objective-C based code gradually to Swift and envisioned a rules-based system where you would encapsulate game type-specific logic in discrete units that can be swapped out at runtime. It has worked out beautifully.

Now we're moving to real-time interactive multi-player games using Firestore live updates. This has also meant moving the app from a custom back-end API to using Firestore and Firebase storage.

The good:
* Unit tests for rules system allowed moving forward faster without the fear of breaking things. Of course, there could always be more unit tests.
* Feature flags in the main branch enable experimenting while delivering public releases.
* Abstracting back-end communication from core game logic allowed for an easier transition from the own API to Firestore saving.

Maxima iOS Estonia

An app that enables you to use your phone as a scanner in retail stores. You can perform touchless checkout using an in-store POS machine.

I extended and modernized the existing iOS codebase, moving the project to the Swift Package Manager-based feature-specific module packages. With new features sneaking in SwiftUI and the composable architecture, I extended and modernized the existing iOS codebase.

I also implemented a touchless checkout flow. It is amazing that the original iOS implementation idea worked.

Your Daily Calories

This is a personal project for calorie tracking.

Based on your fitness goals, you may want to target consumed calorie deficit or surplus. Using Apple Watch, you will be given your basal and active calories burned.
Your daily calories' information will combine calories burned and consumed and project your deficit or surplus target in a 24-hour window. This will allow you to make educated decisions on how to adjust your activity or eating.

The food database will be built by yourself, considering a very tailored list of products specific to your region and preferences: over the last two years, I built a list of 350 foods and products.

Everything is backed up to iCloud and there are no third-party services involved.

HealthKit, SwiftUI, UIKit, CoreData, CloudKit, WidgetKit, IAP

Taxify iOS (Bolt)

Taxify gets you a taxi at the push of a button. The company is taking off at the moment in Europe. I led development for the native rewrite for version 2.0.

Technical notes: Core Location, Core Data, Google Maps SDK, AFNetworking


A simple ten-pair puzzle game. Personal project to get familiar with SpriteKit on iOS. For version 1.2, the whole project was rewritten in Swift.

Technical notes: Swift, SpriteKit, iAd


Estonia's biggest beer blog on iOS devices. It pulls posts from tartugambrinus.blogspot.com using Blogspot API. Done in cooperation with owner of the blog. The iPad version runs in kiosk mode also browsable in the beer shop owned by the blog writer.

Technical notes: Core Data, AFNetworking Blogspot API, Guided Access, Images Caching, UIKit
2001 - 2003

Bachelor's Degree in IT

Tallinn Technical University - Tallinn


HealthKit, SpriteKit, Braintree API, Google Maps


Interface Builder, Xcode, Git, GitHub


iPhone SDK, Core Data, StoreKit, Core Location, CloudKit, SwiftUI, Spring, MapKit, UIKit


iOS, Mapbox


Swift, Objective-C


Cloud Firestore, SQLite


REST, Object-oriented Programming (OOP)


iPad, The Composable Architecture (TCA), Mobile App Development, iBeacon, Widgets, Mobile Ads

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