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John R. Kosinski, Software Developer in Chiang Mai, Thailand
John R. Kosinski

Software Developer in Chiang Mai, Thailand

Member since October 28, 2015
As a veteran full-stack developer, John's great breadth and depth of experience include cryptocurrency, IoT, Blockchain, and mobile projects. His foundation is in C and C++ with many years of experience in .NET. His work experience up until 2009 was in the NYC and NYC area; since 2009, he's been living abroad and working remotely. Currently, finishing up a brief hiatus to study Blockchain and smart contract development.
John is now available for hire



  • C#, 16 years
  • JavaScript, 16 years
  • Microsoft SQL Server, 16 years
  • Agile Software Development, 8 years
  • Scrum, 5 years
  • REST, 4 years
  • Android, 2 years
  • Xamarin, 2 years
Chiang Mai, Thailand



Preferred Environment

100% Flexible

The most amazing...

...project I've worked on is one that combines augmented reality, neuro-linguistic programming, facial recognition, and machine learning.


  • Senior Node.js Developer

    2017 - PRESENT
    • Developed, updated, and continuing to maintain an automated cash-and-carry arbitrage trading system for cryptocurrency exchanges. Supports Bitmex and Bitfinex, several types of trading (mainly cash-carry arbitrage) supported.
    • Built a system of three Node.js applications on Heroku and several AWS lambdas over the course of a few months to implement a unique marketing "sell-it-before-implementing-it" system.
    • Created an on-the-fly image generator using Node.js with Gifsicle and WebShot to generate customized promotional "coins" for use on the site.
    Technologies: Node.js
  • IoT Engineer

    2018 - 2019
    Jaber Medical
    • Contributed to networked embedded development on IoT devices that were connected to a central server; not at liberty to discuss details at the moment.
    Technologies: IoT, C++, Arduino, Node.js, AWS, DynamoDB, Embedded, ESP8266, ESP32
  • Alexa Developer

    2018 - 2018
    Anguleris Technologies
    • Developed a rich Alexa app that will allow customers to run spoken English queries against a complex product database.
    Technologies: Alexa, AWS, Node.js
  • Alexa Developer

    2017 - 2018
    Sterling VC
    • Developed and brought to market an Alexa skill for retrieving New York sporting news updates.
    Technologies: Alexa, Node.js, AWS
  • R&D Manager

    2017 - 2018
    • Developed Alexa Skills for Amazon Dot/Echo.
    • Worked with ESP8266 embedded programming with Arduino IDE.
    • Configured a TLSv1.2 WebSocket security.
    • Developed MQTT communication with AWS IoT cloud.
    • Created a voice-activated smart-home lighting system.
    Technologies: IoT, Alexa, AWS, ESP8266, Embedded C++, Arduino
  • Freelance Senior Xamarin Developer

    2015 - 2017
    Under NDA (via Toptal)
    • Developed from scratch a Xamarin iOS application that controls large-scale SCADA irrigation systems via a Java middle tier.
    • Built the MVP's architecture and prepared a plan to facilitate cross-platform ports.
    • Created a tight system of synchronizing long-running tasks with the server side, across multiple connections or app sessions.
    Technologies: Xamarin iOS, WebSockets
  • Mobile Developer (Remote)

    2014 - 2016
    • Developed a Webby-winning eCommerce iPad application using Xamarin iOS.
    • Added new features on a legacy Objective-C app.
    • Installed new features on a legacy Android app.
    • Consolidated the legacy apps into a new Xamarin unified platform.
    Technologies: Xamarin iOS, Objective-C iOS, Java Android, Xamarin Android, .NET, Selendroid, Jira, Scrum
  • Senior Developer | Team Leader

    2012 - 2014
    Manao Software
    • Managed a team of developers to produce a REST/JSON front-end to a unique SAP-querying interface.
    • Designed the architecture for the above software using .NET Web API MVVM with NHibernate.
    • Managed a team to develop the above software in .NET.
    • Directed the QA unit-testing using SoapUI.
    Technologies: .NET, REST Services, JSON, MVVM, Knockout.js, jQuery, Soap UI, TDD, Scrum, JIRA, Perforce, DDD
  • Software Development Manager

    2009 - 2012
    • Redesigned the rate providers' pulling subsystem.
    • Developed ISAPI filters for the website.
    • Built a prototype mobile/web app.
    • Handled the day-to-day process of development and quality control.
    • Managed a team of 16-20 developers.
    Technologies: .NET, C++, JavaScript, SQL Server, PHP, VB.NET, ISAPI, Android
  • Senior Developer

    2007 - 2009
    Morgan Stanley (NYC)
    • Performed the application and web service programming in C# and VB.NET.
    • Interfaced .NET software with legacy COBOL programs.
    • Wrote the GUI design/programming in ASP.NET and JavaScript.
    • Developed software to manage fixed income securities based on currency exchange models.
    • Designed service-based architecture linking .NET applications to core mainframe services.
    Technologies: .NET, C#, VB.NET, JavaScript, COBOL, SOAP Web Services
  • Senior Software Architect

    2003 - 2007
    Braveline Technology (NYC)
    • Developed an internal image server that's still in use and well-regarded.
    • Wrote an eCommerce object-oriented redesign.
    • Developed an internal component library (parts of which are still in use).
    • Serviced clients in various industries including private equity, financial services, entertainment, and accounting.
    Technologies: C#, VB.NET, C++, VB6, SOA
  • Junior Instructor

    2001 - 2003
    SetFocus LLC (NYC)
    • Researched topics to present to students.
    • Assisted the senior instructor in preparing course material.
    • Delivered and and helped to deliver course material to students.
    • Assessed and graded students' work.
    • Became MCT certified.
    Technologies: .NET, SQL Server, COM


  • Bitcoin Payments (Development)

    A simple Bitcoin payment acceptance module in Node.js for self-educational and demonstration purposes. It creates a wallet address, monitors the Bitcoin network for payment and confirmation, and broadcasts events for progress notifications.

  • Crypto Champ (Development)

    An implementation of an Ethereum smart contract and associated Oracle for self-educational and demonstration purposes. It accepts bets for fictitious boxing matches then calculates and distributes winnings. It also includes a web3.js front-end (which is still in development as of this writing).

  • Minacoin (Development)

    This is a broad-strokes example—for educational purposes only—of the very basic essential workings of a cryptocurrency, coded in Node.js. It includes a Blockchain functionality, a P2P distribution, and a test client; based on the Bitcoin model.

  • Happy-try-catch (Development)

    A generic try/catch/finally library utility module for Node.js. It is also available on npm:

  • Node.js: Async-interval-time (Development)

    A generic library utility module for the timing of synchronous or asynchronous tasks. It is also available on npm:

  • Esp8266-discovery (Development)

    A generic example for the discovery of an esp8266 on the WiFi network; includes an Android client and esp8266 (Arduino) code.

  • IoT/Alexa Demo (Development)

    This is an IoT demo. This is code to control your Samsung TV remote to turn your TV off and on, using an Echo device and code embedded on an ESP8266 chip.

    Associated with Toptal blog article:

  • Ethereum Oracle Contracts: Can We Trust the Oracle? (Publication)
    The whole point of smart contracts is that they need to be more secure and efficient than traditional contracts. So where do smart contract oracles fit in? In the final installment of our three-part series, Toptal Blockchain Developer John R. Kosinski explains the role of oracles in the evolution of trust.
  • Ethereum Oracle Contracts: Solidity Code Features (Publication)
    Solidity is the programming language of choice for Ethereum and the de facto industry standard for smart contract development. In the second article of our three-part series, Toptal Blockchain Developer John R. Kosinski takes a closer look at Solidity quirks and features, explaining how to make the most of it.
  • Ethereum Oracle Contracts: Setup and Orientation (Publication)
    Oracles are changing the way we view and create smart contracts. How do we implement them in Ethereum, using nothing but Solidity and standard dev tools? In the first article of our three-part series, Toptal Blockchain Developer John R. Kosinski explains how to get started and compile a smart contract with oracles.
  • Get Started with IoT Development: An ESP8266 Arduino Tutorial (Publication)
    In this tutorial, Toptal Freelance Software Engineer John R. Kosinski will demonstrate a simple Amazon Alexa hack using quintessential Arduino skills and basic hardware.


  • Languages

    C#, JavaScript, C++, Solidity, Python, HTML5, Java, XML, Perl, Objective-C, C, Assembly, Go, Python 3, N, COBOL, XPath, PHP
  • Frameworks

    .NET, ASP, ASP.NET, Knockout.js, Sencha Touch
  • Libraries/APIs

    Node.js, Amazon API, jQuery, MailChimp API, Mixpanel API, TensorFlow, Keras
  • Tools

    Android Studio, Microsoft Visual Studio, Mongoose, Xcode, Jira, NPM, AWS SES, MQTT, SoapUI
  • Paradigms

    Agile Software Development, Scrum, REST, Model View Viewmodel (MVVM), Model View Controller (MVC), Design Patterns, Kanban
  • Storage

    JSON, Microsoft SQL Server, MySQL, NoSQL, MongoDB
  • Other

    RESTful APIs, Smart Contracts, Ethereum Smart Contracts, Blockchain Technology, Xamarin Forms, SOAP, WebSockets, ESP8266, Internet of Things (IoT), HTTP, eCommerce, Trading, Banking & Finance, ESP32, RTOS, Customized Blockchains, Machine Learning, Unix Shell Scripting, IoT Protocols
  • Platforms

    AWS IoT Core, Linux, Arduino, Amazon Alexa, Android, iOS, Blockchain, Web, Xamarin, Blockchain Platforms, AWS IoT


  • Bachelor of Science degree in Computer Science
    1993 - 1998
    University of Delaware - Newark, DE, USA
  • PFC USMC in Basic Military Skills
    1996 - 1996
    Parris Island Marine Corps Recruit Depot (MCRD) - Parris Island, SC, USA
  • MCT (Microsoft Certified Trainer)
    FEBRUARY 2003 - FEBRUARY 2004
  • MCSD (Microsoft Certified Solutions Developer)
    MAY 2001 - MAY 2005
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