Publication
Ethereum Oracle Contracts: Can We Trust the Oracle?
https://www.toptal.com/developers/ethereum/oracle-contracts-tutorial-pt3
John is currently unavailable
John R. Kosinski
Verified Expert in Engineering
Full-stack Developer
Chiang Mai, Thailand
Toptal member since February 9, 2016
Bio
John is a senior technologist and system owner specializing in high‑risk, high‑constraint environments across blockchain, financial markets, and large‑scale distributed systems. He is known for owning systems end‑to‑end where failure carries real financial, operational, or reputational consequences. John brings ideas from concept to production under risk, constraint‑driven architecture, and decision ownership in ambiguous environments.
Portfolio
EVERYTHING AUTO NEW YORK LLC
Blockchain, Blockchain Design, Blockchain Architecture, Blockchain Development...
Hamza Labs
Agile, eCommerce, Medusa, TypeScript, Next.js, Solidity, Blockchain...
Lingling Jiang
Large Language Models (LLMs), Technical Leadership...
Experience
- Software Development - 20 years
- .NET - 16 years
- C++ - 16 years
- Design Patterns - 14 years
- Technical Leadership - 7 years
- Banking & Finance - 5 years
- TypeScript - 4 years
- Solidity - 4 years
Preferred Environment
Scrum, Agile, Test-driven Development (TDD), Agile Software Development, Fintech, System Architecture, Blockchain
The most amazing...
...thing I've done recently was develop a blockchain financial instrument that was one of the 1st of its kind.
Work Experience
Prediction Market Strategy Developer
2025 - PRESENT
EVERYTHING AUTO NEW YORK LLC
- Built a prediction markets trading platform with a backtesting engine, automated probability engine, and live trading strategies in a TypeScript monorepo with 4+ packages, CI/CD pipelines, and automated testing.
- Developed an iterative, multi-threaded backtesting engine and enhanced it with Bayesian optimization for automated parameter tuning.
- Designed modular trading strategies with configurable parameters that could be optimized through the backtesting framework.
- Implemented Avellaneda-Stoikov and Order Flow Imbalance market-making strategies that demonstrated positive performance in both backtesting and live trading.
- Leveraged AI agents to assist with strategy development, backtesting, and trade execution workflows.
Technologies: Blockchain, Blockchain Design, Blockchain Architecture, Blockchain Development, Artificial Intelligence (AI), Quantum Computing, TypeScript, Python, Jupiter, Google Cloud Platform (GCP), Claude Code, GitHub Actions, Single Sign-on (SSO), Full-stack Development, Prediction Markets, Agentic Coding, OpenAI API, AI Tools, Data Science, AI Programming, Agentic AI Systems, Real-time Data, Amazon S3 (AWS S3), Claude, Quantitative Trading, Trading Bots, Quantitative Finance, Quantitative Modeling, Trading Robots, Back-end Development, Database Schema Design
CTO
2023 - PRESENT
Hamza Labs
- Co-founded the company and served as CTO, leading a six-developer team across front end, back end, smart contracts, and payments infrastructure for hundreds of monthly users, 20+ sellers, thousands of SKUs, and $5,000-$10,000 monthly throughput.
- Conceived, architected, and delivered a production cross-chain crypto payment system using intents, single-use HD holding wallets, chain listeners, event-driven processing via EventBridge/SQS, idempotent verification, and canonical escrow settlement.
- Architected and led development of a live multitenant eCommerce storefront using MedusaJS, NestJS, Next.js, and TypeScript, with wallet checkout, seller identity, seller admin, full order flow, and AWS/PostgreSQL/Redis/Kubernetes infrastructure.
- Designed and deployed Solidity escrow contracts to Optimism as the canonical settlement layer for the marketplace, with a consent-based release/refund state machine, protocol fees, seller-delegated permissions, and Hats Protocol role model.
- Co-designed the platform's tokenomics architecture, including seller escrow rent, initial seller mint, and dispute-resolution incentive mechanisms.
- Built and owned Kubernetes-based production infrastructure covering back-end services, payment listeners, dev/staging/production environments, CI/CD pipelines, monitoring, and alerting.
Technologies: Agile, eCommerce, Medusa, TypeScript, Next.js, Solidity, Blockchain, Smart Contracts, Ethereum, Blockchain Architecture, Blockchain Development, Blockchain Design, Distributed Systems, Event-driven Architecture, Observability, Cloud Architecture, Multitenancy, Agile Software Development, CTO, Claude Code, GitHub Actions, Marketplaces, Payment APIs, Single Sign-on (SSO), Full-stack Development, ChatGPT, Engineering Management, Backlog Management, API Gateways, OpenAI, Startups, AI Programming, Leadership & Coaching, DevOps, EventBus, Workflow Automation, n8n, Amazon S3 (AWS S3), Claude, Serverless, Webhooks, Back-end Development, Database Schema Design, Escrow, Payments, GitHub
Technical Lead/Solutions Architect
2026 - 2026
Lingling Jiang
- Created technical architecture plan, details, and diagrams as part of a financial and market discovery for an AI-powered personal finance and banking application.
- Leveraged my experience in AI, crypto/blockchain, and fintech technical discovery and architecture for the overall technical scope of the project, including banking integrations, crypto integrations, and architecture for AI agents.
- Created detailed C4 diagrams, component diagrams, and technical project breakdowns and estimates.
Technologies: Large Language Models (LLMs), Technical Leadership, Retrieval-augmented Generation (RAG), Full-stack, Architecture, Fintech, Mobile Apps, Plaid, Open Banking, Cryptocurrency, ChatGPT, Model Context Protocol (MCP), Anthropic, Financial System Implementation, AI Programming, AI Architecture, Agentic AI Systems, AI Automation, Back-end Development
CTO | Chief Engineer
2025 - 2026
Spencer Secola
- Developed a proprietary language (QSDL) for representing complex stocks, futures, and currency trading strategies in JSON, with a completely validated and versioned JSON schema, dynamic document compilation, and validation modules.
- Built a large language model (LLM) agent capable of converting natural language trading strategy descriptions to a complex proprietary trading strategy language QSDL that I developed for this project.
- Developed and documented system architecture for a backtesting data ingestion and execution pipeline on the Google Cloud Platform (GCP).
- Architected a multi-platform code generation system that compiles proprietary QSDL (Quant Strategy Definition Language) JSON specifications into executable trading algorithms for MetaTrader 5 (MQL5), NinjaTrader (C#/NinjaScript), and PineScript.
- Developed an AST transformation pipeline that converts platform-agnostic trading logic into platform-specific code with accurate indicator calculations, state management, and order execution logic across multiple trading platforms.
- Designed and implemented a TypeScript-based monorepo using pnpm workspaces with modular packages including QSDL schema validation, AI-driven natural language strategy generation (qsdlgen), multi-platform code compilation (codegen), and REST API.
- Established CI/CD infrastructure with automated testing, CodeQL security scanning, and comprehensive developer documentation covering system architecture, QSDL design philosophy, AST generation, and platform integration guides.
Technologies: Algorithmic Trading, Architecture, MQL5, C#, Technical Design, C#.NET, Backtesting Trading Strategies, API Integration, Visual Builders, Fractional CTO, MQL4, Pine Script, NinjaTrader, MetaTrader, TradingView, cTrader, Cloud Infrastructure, Large Language Models (LLMs), Agile, MetaTrader 5, AI Agents, Cloud Architecture, Google Cloud Platform (GCP), Claude Code, GitHub Actions, Single Sign-on (SSO), Agentic Coding, Prompt Engineering, OpenAI API, ChatGPT, Model Context Protocol (MCP), Anthropic, OpenAI, AI Programming, AI Architecture, Agentic AI Systems, AI Automation, Claude, Back-end Development, Database Schema Design
Senior Blockchain Developer
2025 - 2026
PFP Media LLC
- Architected an event-driven Solana decentralized finance trading engine in Rust, leveraging WebSocket RPC subscriptions for sub-second on-chain transaction monitoring, with intelligent trade routing and Jupiter DEX aggregator for optimal execution.
- Built an asynchronous position management system using Tokio runtime with concurrent execution, dynamic risk controls, time-decay exits, and real-time P&L tracking via Jupiter price oracles.
- Developed algorithmic trading strategy engine with supply-weighted position sizing, liquidity depth analysis via Helius DAS API, configurable slippage parameters, priority fee optimization, and MEV protection via Jito tip accounts.
- Built a currency trading analytics platform analyzing Solana blockchain transactions using Helius API to parse swap transactions across DEXs (Jupiter, Orca, Raydium), implementing a matching algorithm that calculates P&L stats and risk metrics.
- Developed a comprehensive reporting and visualization toolkit generating CSV exports, interactive Jupyter notebook visualizations (P&L distributions, hold time analysis, cumulative returns), and statistical reports with 15+ performance metrics.
Technologies: Blockchain, Blockchain Platforms, Solana, Blockchain Design, Decentralized Exchanges (DEXs), Cryptocurrency Wallets, Rust, Python, Jupiter, Python 3, Cloud Architecture, Google Cloud Platform (GCP), Single Sign-on (SSO), Full-stack Development, Anthropic, Claude
Software Developer
2023 - 2023
Leeds Rising
- Developed PyDAS: a robust, complete, and well-tested Python API to the DAS trading platform API for buying, selling, borrowing, and short-selling US stocks.
- Developed and rigorously tested an algorithmic trading system using the PyDAS API, which can specify dynamic trading strategies, including a configurable Trigger and configurable plug-and-playable Trade logic.
- Implemented strategies for borrowing and short-selling illiquid stocks on the Nasdaq and NYSE. Deployed and tested those strategies on the live market.
Technologies: Software Development, API Integration, Trading, C#, Python, Trading Systems, Stock Trading, Multithreading, High-frequency Trading (HFT), Low-latency Software, Quantitative Trading, Quantitative Finance, Trading Robots
DeFi Architect
2022 - 2023
Patagon Management LLC
- Acted as principal architect and founding engineer for Stream Finance's on-chain US Treasury/fixed-income investment protocol. It later became the foundation for XUSD, a same-company stablecoin with seven-figure financial exposure.
- Modeled a full fixed-income lifecycle on-chain: stablecoin deposits, Vault Token issuance, Deposit/Locked/Withdraw phases, sequential rounds, rollover-based compounding, and admin-controlled exchange-rate/yield updates.
- Conducted technical research to assess the feasibility of various potential automated hedge fund strategies in the blockchain space.
- Built multi-layer contract testing: Hardhat unit/integration tests, stochastic simulations across multiple users and rounds verified against an off-chain ledger, Echidna invariant tests, plus manual penetration testing.
- Architected AWS operational infrastructure: chain listeners, SQS/Lambda deposit finalization with idempotency, EventBridge event-driven workflows with human approval gates, Amazon S3 audit logs, production invariant monitors, and SNS/SES alerting.
Technologies: Solidity, Blockchain, Smart Contracts, Algorithmic Trading, Algorithmic Trading Analysis, Hedge Funds, Web 3.0, Application Architecture, Automated Trading Software, Back-end, REST, Git, Express.js, Web Security, Penetration Testing, Decentralized Systems, Decentralized Finance (DeFi), ERC-20, Web3.js, Technical Architecture, Solution Architecture, Fintech, Lambda Functions, Amazon Simple Notification Service (SNS), Blockchain Architecture, Blockchain Development, Blockchain Design, Cloud Architecture, GitHub Actions, API Gateways, Leadership & Coaching, DevOps, Amazon S3 (AWS S3), Back-end Development, Database Schema Design
Technical Consultant
2022 - 2023
AxiomSys
- Planned and estimated project packages for non-fungible and fungible token development, front-end minting and administration websites with React, and security audits of smart contracts.
- Researched, planned, and presented the integration of fungible and non-fungible tokens with the Unity game engine back end of a well-known online meeting venue.
- Contacted, vetted, and interviewed blockchain developers, laying the foundations for an elite international team of blockchain warriors.
- Developed, planned, and documented a methodology for security audits of smart contracts.
- Provided expert technical consultation during sales meetings.
Technologies: Solidity, Blockchain, Smart Contracts, Ethereum, Ethereum Smart Contracts, Solana, C#, JavaScript, .NET, Unity, Software Development, Blockchain & Cryptocurrency, Full-stack, Rust, Cryptocurrency, Unix, C#.NET, TypeScript, Crypto, Architecture, React, MetaMask, Rinkeby, Web 3.0, Application Architecture, Automated Trading Software, Back-end, Git, Express.js, R&D, Presentations, Decentralized Systems, ERC-20, Web3.js, Technical Architecture, Solution Architecture, PostgreSQL, Go, Lambda Functions, Blockchain Architecture, Blockchain Development, Blockchain Design, ChatGPT, Amazon S3 (AWS S3), Back-end Development
Senior C# Web3 Developer
2022 - 2022
Garbles Labs
- Ported the TypeScript SDK to C#/.NET for the well-known Solana market maker Orca Whirlpools to be used in the Unity game engine; made it open for community use.
- Developed the SDK for .NET, refactored as necessary, and added a suite of automated tests to ensure quality.
- Interfaced with the Rust smart contracts and modified the Rust code as needed for testability.
Technologies: C#, Unity, C#.NET, TypeScript, Blockchain, Rust, Node.js, JavaScript, Smart Contracts, Gaming, .NET, Decentralized Systems, Web3, ASP.NET Core, Blockchain Development, Back-end Development
Enterprise C++ Developer
2019 - 2022
Alteryx
- Developed and maintained the core C++ back-end engine of Alteryx's enterprise data analytics platform, resolving customer and internal defects and delivering new features in C++ 11 on Windows and Linux.
- Took ownership of some of the most long-standing and difficult defects in the Alteryx engine — performing deep root cause analysis, documenting findings thoroughly, and implementing regression tests to prevent recurrence.
- Maintained cross-platform C++ 11 compatibility across Windows and Linux using Modern C++, Boost, STL, ATL, and MFC in a high-stakes commercial product engine.
- Managed end-to-end defect lifecycle — triage, investigation, root cause analysis, fix, test, and cross-team coordination — for a commercial C++ engine with enterprise customer impact.
- Worked across team boundaries at Alteryx to gather information, align on fixes, and drive resolution of defects that crossed ownership lines.
Technologies: C#, .NET, Microsoft Visual Studio, C++11, C++, Test-driven Development (TDD), Defect Management, Microsoft SQL Server, Agile Software Development, Unit Testing, Software Development, Design Patterns, Complex Problem Solving, Linux, JavaScript, APIs, CI/CD Pipelines, SQL, Unix, Integration, C#.NET, Architecture, Algorithms, MySQL, Application Architecture, API Integration, Back-end, Git, Confluence, Visualization, Data Engineering, Technical Architecture, Solution Architecture, Multithreading, MSBuild, Leadership & Coaching, Back-end Development
IoT Engineer
2018 - 2019
Jaber Medical
- Developed ESP8266 and ESP32 hardware prototypes for a unique and proprietary hospital emergency room communications system. The prototype included IR, WiFi, and an RFID chip scanner.
- Architected and developed embedded networked software for the ESP32/ESP8266 for the hardware prototype, with Arduino and RTOS in C, interacting with WiFi, IR, and RFID readers.
- Researched and made decisions and tradeoffs regarding software and hardware requirements, working closely with the client to meet their needs.
Technologies: Amazon Web Services (AWS), ESP32, ESP8266, Embedded Systems, Amazon DynamoDB, Arduino, C++, Internet of Things (IoT), C, JavaScript, Agile Software Development, Node.js, Unit Testing, AWS IoT, Real-time Operating System (RTOS), MQTT, Software Development, Design Patterns, Embedded C++, Complex Problem Solving, Microservices, Linux, APIs, Full-stack, TypeScript, Architecture, Amazon EC2, AWS Lambda, Application Architecture, NoSQL, REST, Git, Express.js, Technical Architecture, Solution Architecture, Lambda Functions, Amazon Simple Notification Service (SNS), Back-end Development
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.
- Architected and developed the back end using DynamoDB on AWS, Node.js, and AWS SDK, to automate back-end data imports from providers and synchronize with the database.
- Developed a rigorous automated testing suite to ensure continued quality.
Technologies: Amazon Web Services (AWS), Amazon Alexa, JavaScript, Agile Software Development, Unit Testing, AWS IoT, Software Development, Design Patterns, Complex Problem Solving, Amazon EC2, AWS Lambda, Amazon DynamoDB, Application Architecture, NoSQL, Git, Lambda Functions, Back-end Development
Alexa Developer
2017 - 2018
Sterling VC
- Developed and brought to market an Alexa skill for retrieving New York sporting news updates for Alexa Echo, Dot, and Show.
- Used DynamoDB, AWS Lambda scripts in Node.js, and AWS SDK to architect a back-end system for retrieving data from providers and keeping the database synchronized.
- Architected and implemented voice-activated UI for Alexa, as well as a visual UI for Alexa Show.
Technologies: Amazon Web Services (AWS), Node.js, Amazon Alexa, Agile Software Development, Unit Testing, AWS IoT, Software Development, Design Patterns, Complex Problem Solving, JavaScript, Full-stack, Amazon EC2, AWS Lambda, Amazon DynamoDB, Application Architecture, Git, Lambda Functions
R&D Manager
2017 - 2018
Futronix
- Researched and directed research in the development of Alexa Skills for Amazon Echo Dot and how they could be integrated into existing company products.
- Researched possibilities of replacing the usage of proprietary chips in some of the company's existing products with less-expensive ESP8266 and ESP32 chips.
- Created a prototype module for integrating voice commands into the interfaces of an existing home lighting product, utilizing AWS and Alexa APIs.
- Presented and documented research findings, as well as new proposals for technological product improvements.
Technologies: Amazon Web Services (AWS), Amazon Alexa, Arduino, Embedded C++, ESP8266, Internet of Things (IoT), JavaScript, .NET, Agile Software Development, Node.js, Unit Testing, AWS IoT, Real-time Operating System (RTOS), Embedded Systems, MQTT, ESP32, Software Development, Design Patterns, .NET Core, Complex Problem Solving, Linux, C#, Unix, Architecture, Amazon EC2, AWS Lambda, Amazon DynamoDB, Application Architecture, GraphQL, Git, Prediction Markets, Visualization, ASP.NET Core, Technical Architecture, Solution Architecture, PostgreSQL, Lambda Functions, Amazon Simple Queue Service (SQS), Database Schema Design
Automated Trade Analyst
2016 - 2017
Event Driven Investor
- Improved algorithms for analyzing the correlation between distinct financial asset price series.
- Corrected Pearson's coefficient calculations to discover the correlation between stock trading pairs.
- Refactored the C# application code for better organization, extensibility, and modularity.
- Added automated tests to discover bugs in the existing codebase. Analyzed and fixed the bugs found.
Technologies: C#, SQL, .NET, Interactive Brokers API, Infragistics, Azure, MySQL, Stock Trading, Trading, Finance, Stock Analysis, Trading Systems, ASP.NET Core, Fintech, Multithreading, Amazon S3 (AWS S3), Quantitative Trading, Quantitative Modeling, Trading Robots, Back-end Development
Node.js Developer
2016 - 2017
Private Client
- Developed a full and profitable algorithmic trading system to exploit arbitrage opportunities between cryptocurrency futures and spot markets.
- Tested and debugged the system, using APIs for various exchanges.
- Developed plugins to allow the system to be used on various popular crypto futures and spot exchanges.
Technologies: Blockchain, Trading, Arbitrage, Futures, JavaScript, Agile Software Development, Node.js, Unit Testing, Software Development, Design Patterns, Complex Problem Solving, Docker, Linux, C#, .NET, Microsoft Visual Studio, Ethereum Smart Contracts, Decentralized Finance (DeFi), APIs, Blockchain & Cryptocurrency, Full-stack, Bots, Binance API, Cryptocurrency, Unix, Integration, TypeScript, Crypto, Architecture, Rinkeby, Amazon EC2, Amazon RDS, AWS Lambda, Amazon DynamoDB, Algorithmic Trading, Algorithmic Trading Analysis, Application Architecture, Automated Trading Software, REST, Git, Express.js, Prediction Markets, Visualization, Twilio, Trading Systems, Decentralized Systems, Bitcoin, Technical Architecture, Solution Architecture, Multithreading, Lambda Functions, Amazon Simple Notification Service (SNS), Blockchain Architecture, Blockchain Development, High-frequency Trading (HFT), Full-stack Development, DevOps, Real-time Data, Quantitative Trading, Trading Bots, Quantitative Finance, Trading Robots, Back-end Development, Database Schema Design
Freelance Senior Xamarin Developer
2015 - 2017
Aquamonix
- Built Aquamonix's Xamarin iOS application from scratch - a mobile control interface for large-scale SCADA irrigation systems communicating through a Java middle tier.
- Architected the MVP for Aquamonix's industrial irrigation control app and designed a cross-platform portability plan to support future Android and other platform ports.
- Engineered a robust, long-running task synchronization system that maintained consistent irrigation job state across multiple WebSocket connections and app sessions - a critical reliability requirement in an industrial control context.
- Developed mobile control software for industrial-scale SCADA irrigation systems—a domain requiring reliability guarantees well beyond typical consumer app expectations.
Technologies: WebSockets, C#, JavaScript, .NET, Microsoft Visual Studio, Agile Software Development, Node.js, Unit Testing, Software Development, Design Patterns, Xamarin.iOS, Complex Problem Solving, Full-stack, SQL, C#.NET, REST APIs, Application Architecture, Back-end, REST, Git, Mobile Apps, Xamarin.Android, Solution Architecture, Full-stack Development, Back-end Development
Mobile Developer (Remote)
2014 - 2016
Door3/FreshDirect
- Developed a Webby-winning eCommerce iPad application using Xamarin.iOS to replace the company's legacy Objective-C application and to unify the Android and iOS legacy apps into a single codebase.
- Developed features for both the back and front end using Xamarin iOS, with a small team.
- Helped to architect the framework to combine the codebases of two legacy apps into one unified Xamarin app.
- Diagnosed and fixed defects in the company's legacy Android and iOS applications.
Technologies: Java, Scrum, Jira, Android, iOS, Xamarin, C#, JavaScript, Agile Software Development, Node.js, Unit Testing, eCommerce, Software Development, Model View Controller (MVC), Design Patterns, Model View ViewModel (MVVM), Xamarin.iOS, Complex Problem Solving, .NET, APIs, Full-stack, SQL, Integration, C#.NET, Architecture, REST APIs, Application Architecture, API Integration, Back-end, Git, Mobile Apps, Xamarin.Android, ASP.NET Core, Technical Architecture, Solution Architecture, Enterprise Architecture, Marketplaces, Payment APIs, Back-end Development, Database Schema Design
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 for EveryAngle.
- 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; interfaced with the client's executive team.
Technologies: RESTful Services, Domain-driven Design (DDD), Perforce, Jira, Scrum, Test-driven Development (TDD), User Interface (UI), SOAP, Knockout (Knockout.js), Model View ViewModel (MVVM), JSON, C#, Microsoft Visual Studio, Agile Software Development, ASP.NET, Unit Testing, WebSockets, Software Development, Model View Controller (MVC), Design Patterns, Xamarin.iOS, Leadership, Technical Leadership, Team Leadership, Lean Project Management, .NET Core, Complex Problem Solving, Microservices, C++, Linux, .NET, APIs, HTML, Unix, C#.NET, Architecture, Windows, ASP.NET MVC, REST APIs, Amazon RDS, Application Architecture, API Integration, Azure, Back-end, REST, Git, Express.js, Mobile Apps, ASP.NET Core, Technical Architecture, Solution Architecture, Multithreading, .NET 4, Enterprise Architecture, SQLite, Windows Presentation Foundation (WPF), Payment APIs, Full-stack Development, Engineering Management, SaaS, Backlog Management, API Gateways, Leadership & Coaching, DevOps, Amazon S3 (AWS S3), Back-end Development, Database Schema Design
Software Development Manager
2009 - 2012
HotelTravel.com
- Architected, oversaw, and wrote code (for some portions) for a full overhaul of the underlying back-end booking engine, a complex system for integrating data from various categories of hotel rate providers.
- Designed and implemented test-driven policies for automated and manual testing of new software components to ensure the quality of each component's development and the correctness of its implementation into the overall system.
- Mentored individual developers in software micro-design (e.g., design patterns), new technologies (such as mobile), and best practices for efficiency, security, and scalability.
Technologies: Internet Server Application Programming Interface (ISAPI), Android, PHP, Microsoft SQL Server, C++, C#, Microsoft Visual Studio, Agile Software Development, ASP.NET, Unit Testing, WebSockets, Software Development, Design Patterns, Leadership, Technical Leadership, Team Leadership, Lean Project Management, Complex Problem Solving, Linux, .NET, HTML, SQL, C#.NET, Architecture, Windows App Development, Windows, ASP.NET MVC, REST APIs, IIS, Legacy Software, Application Architecture, Windows Services, API Integration, Azure, Back-end, REST, Object-relational Mapping (ORM), Express.js, Technical Architecture, Solution Architecture, .NET 4, Crystal Reports, WinDev, SQLite, Windows Presentation Foundation (WPF), Full-stack Development, Engineering Management, Backlog Management, API Gateways, Leadership & Coaching, Amazon S3 (AWS S3), Back-end Development, Database Schema Design
Senior Developer
2007 - 2009
Morgan Stanley (NYC)
- Developed back-end logic for a new fixed-income product interface for Morgan Stanley's Global Wealth Management Platform.
- Designed and integrated .NET modules to interface with legacy mainframe systems written in COBOL.
- Pioneered test-driven development policies in the department, implementing rigorous automated tests for various projects.
Technologies: SOAP, JavaScript, Microsoft Visual Studio, ASP.NET, Unit Testing, Banking & Finance, WebSockets, Software Development, Design Patterns, Microservices, C++, .NET, SQL, COM, C#, C#.NET, Architecture, Windows App Development, Windows, ASP.NET MVC, REST APIs, IIS, Legacy Software, Windows Services, API Integration, Back-end, REST, Object-relational Mapping (ORM), Fintech, Multithreading, Enterprise Architecture, Crystal Reports, API Backwards Compatibility, Back-end Development
Experience
Bond Vault, Foundation for Successful Stablecoin
The bond vault, the foundation for a stablecoin that commanded hundreds of thousands in TVL at its peak.
PROJECT LINKS:
• Streamprotocol.money
• App.streamprotocol.money
• Etherscan.io/address/0xd86FFB404147163e19E010a0e9d4995E0e36F335
• Etherscan.io/address/0xADF789E61Bf38c463e4bA5B2B6E9C1Af6659e11b
• Etherscan.io/address/0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48
• Etherscan.io/address/0x746430119DA3EA0e398b93059e96F21bfabAa8a4
https://etherscan.io/address/0xD48425B7fb702F571D872f4b7046B30c9FA47e15
• Bscscan.com/address/0x3daa26E70383B37E41434a8bF8e8bF3A335c144A
• Bscscan.com/address/0xB95Bc0d1057a43ACF608805c6D4e3e234e4d4C1b
• Bscscan.com/address/0x8ac76a51cc950d9822d68b83fe1ad97b32cd580d
• Bscscan.com/address/0x2A7aD6908A08dD19D6c5090aA86E7c7E61C3e7F4
• Bscscan.com/address/0x2900E387152a22370F482a0640701e1B41cc0896
• Github.com/jrkosinski/evm-bond-vault
PROJECT LINKS:
• Streamprotocol.money
• App.streamprotocol.money
• Etherscan.io/address/0xd86FFB404147163e19E010a0e9d4995E0e36F335
• Etherscan.io/address/0xADF789E61Bf38c463e4bA5B2B6E9C1Af6659e11b
• Etherscan.io/address/0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48
• Etherscan.io/address/0x746430119DA3EA0e398b93059e96F21bfabAa8a4
https://etherscan.io/address/0xD48425B7fb702F571D872f4b7046B30c9FA47e15
• Bscscan.com/address/0x3daa26E70383B37E41434a8bF8e8bF3A335c144A
• Bscscan.com/address/0xB95Bc0d1057a43ACF608805c6D4e3e234e4d4C1b
• Bscscan.com/address/0x8ac76a51cc950d9822d68b83fe1ad97b32cd580d
• Bscscan.com/address/0x2A7aD6908A08dD19D6c5090aA86E7c7E61C3e7F4
• Bscscan.com/address/0x2900E387152a22370F482a0640701e1B41cc0896
• Github.com/jrkosinski/evm-bond-vault
Zeppelin: EthGlobal 2023 Hackathon Winner
A blockchain project that I architected and built bridges decentralized finance and eCommerce, providing a gateway for eCommerce sellers to finance their projects using sales of custom NFTs.
Created using Solidity, Hardhat, TypeScript, Tableland, and Next.js.
Created using Solidity, Hardhat, TypeScript, Tableland, and Next.js.
Common NFT Contract Design Anti-patterns
Wrote and published an article on the most common design anti-patterns.
Scanning the blockchain's verified NFTs, I frequently see recurring common anti-patterns. I wrote an article listing what I think are the most common ones, some thoughts about why they occur, and some better alternatives.
Scanning the blockchain's verified NFTs, I frequently see recurring common anti-patterns. I wrote an article listing what I think are the most common ones, some thoughts about why they occur, and some better alternatives.
Security Manager Design Pattern in Solidity
This is an article that I wrote after finishing a defi project about a particular design pattern in Solidity to secure a group of smart contracts. It's a simple pattern that can serve as a helpful introduction for individuals to the concept of modular design in Solidity and how it's a bit different than in traditional OOP.
Ethernaut Solutions
https://github.com/jrkosinski/EthernautThese are solutions to the well-known Ethernaut problems. Exercises published by OpenZeppelin as teaching tools and to assess one's ability to understand EVM and Solidity security vulnerabilities and how to protect against them. These solutions contain full source code with unit tests and explanations.
FreshDirect iOS
An award-winning iOS grocery order/delivery app for the well-known NYC online grocery store, FreshDirect. It was developed with .NET using the Xamarin iOS platform. This app won a Webby in 2015 in the websites and mobile sites category.
Aquamonix iOS
https://apps.apple.com/nz/app/aquamonix/id1166491146An iOS app that allows customers of Aquamonix to interact remotely with their industrial-sized SCADA irrigation systems. I architected and developed from scratch using Xamarin iOS and Android, with C#.
Medium Articles
These are my recent Medium articles, showcasing skills and knowledge in
• blockchain development and architecture
• machine learning and AI
• statistics
• software development and architecture
• communication skills
• blockchain development and architecture
• machine learning and AI
• statistics
• software development and architecture
• communication skills
Preparing and Shaping Timeseries Data for Keras LSTM Input
A two-part article detailing and demonstrating some techniques for pre-processing timeseries data (the example used is stock price historical data) in preparation to use it as input to a Keras long short-term memory (LSTM) neural network.
The preprocessing described and demonstrated includes statistical transformations like scaling, handling outliers, removing the trend, and extracting important features. It also includes the correct way to shape the data into the appropriate number of dimensions.
The article is in two parts:
Part 1: https://medium.com/@john.kosinski/preparing-and-shaping-timeseries-data-for-keras-lstm-input-part-one-5bb882bc2143
Part 2: https://medium.com/@john.kosinski/preparing-and-shaping-timeseries-data-for-keras-lstm-input-part-two-ad17f6ab450
The preprocessing described and demonstrated includes statistical transformations like scaling, handling outliers, removing the trend, and extracting important features. It also includes the correct way to shape the data into the appropriate number of dimensions.
The article is in two parts:
Part 1: https://medium.com/@john.kosinski/preparing-and-shaping-timeseries-data-for-keras-lstm-input-part-one-5bb882bc2143
Part 2: https://medium.com/@john.kosinski/preparing-and-shaping-timeseries-data-for-keras-lstm-input-part-two-ad17f6ab450
Rust API
https://github.com/jrkosinski/rust-apiAn available Rust crate and open-source project that brings the ease and convenience of REST API building modules like FastAPI and NestJS to Rust. Built over Axum and Tokio, it leverages dependency injection and Rust's type system to let developers quickly spin up a utilitarian REST API in Rust, to avoid reinventing the wheel for a common task.
Prediction Markets Trading and Backtesting Engine
An algorithmic trading engine and backtesting and optimization engine for prediction markets.
Algorithmic Strategies: Avellaneda-Stoikov and OFI market-making strategies, optimized algorithmically using historical trade data, and proven profitable in live trading, deploying large amounts of capital with low risk exposure.
Traditional Strategies: Formulated around the market's proven tendency to undervalue the underdog in sports markets, tested, refined, and optimized algorithmically using the backtest optimizer.
Backtest Engine: Stores historical data, runs strategies in batches, generates and saves metrics, and guards against overfitting.
Optimization Engine: uses Bayesian optimization via Optuna to tune parameter values, converging on an optimal configuration for live trading while avoiding overfitting.
Algorithmic Strategies: Avellaneda-Stoikov and OFI market-making strategies, optimized algorithmically using historical trade data, and proven profitable in live trading, deploying large amounts of capital with low risk exposure.
Traditional Strategies: Formulated around the market's proven tendency to undervalue the underdog in sports markets, tested, refined, and optimized algorithmically using the backtest optimizer.
Backtest Engine: Stores historical data, runs strategies in batches, generates and saves metrics, and guards against overfitting.
Optimization Engine: uses Bayesian optimization via Optuna to tune parameter values, converging on an optimal configuration for live trading while avoiding overfitting.
Publication
Ethereum Oracle Contracts: Solidity Code Features
https://www.toptal.com/developers/ethereum/ethereum-solidity-oracle-contracts-pt2
Publication
Ethereum Oracle Contracts: Setup and Orientation
https://www.toptal.com/developers/ethereum/ethereum-oracle-contracts-tutorial-pt1
Publication
Get Started With IoT Development: An ESP8266 Arduino Tutorial
https://www.toptal.com/developers/arduino/esp8266-arduino-tutorial-alexa-hack
Education
1993 - 1998
Bachelor of Science in Computer Science
University of Delaware - Newark, DE, USA
Certifications
OCTOBER 2023 - PRESENT
AWS Certified Solutions Architect – Associate
Amazon Web Services
DECEMBER 2018 - PRESENT
Blockchain Platforms
University at Buffalo & The State University of New York | via Coursera
NOVEMBER 2018 - PRESENT
Decentralized Applications (Dapps)
University at Buffalo & The State University of New York | via Coursera
OCTOBER 2018 - PRESENT
Smart Contracts
University at Buffalo & The State University of New York | via Coursera
OCTOBER 2018 - PRESENT
Blockchain Basics
University at Buffalo & The State University of New York | via Coursera
FEBRUARY 2003 - FEBRUARY 2004
MCT (Microsoft Certified Trainer)
Microsoft
MAY 2001 - MAY 2005
MCSD (Microsoft Certified Solutions Developer)
Microsoft
Skills
Libraries/APIs
Node.js, Web3.js, Amazon API, REST APIs, Interactive Brokers API, Xamarin.Android, OpenAI API, Xamarin.iOS, Mailchimp API, Mixpanel API, TensorFlow, React, Binance API, Keras, TensorFlow Deep Learning Library (TFLearn), Infragistics, LSTM
Tools
Microsoft Visual Studio, ChatGPT, NPM, Jira, MetaMask, Git, Amazon Simple Notification Service (SNS), Claude Code, MSBuild, Claude, GitHub, Perforce, Mongoose, Amazon Simple Email Service (SES), MQTT, SoapUI, Visual Studio, Confluence, Amazon Simple Queue Service (SQS), Crystal Reports, NinjaTrader, Plaid, Microsoft Copilot, n8n
Languages
Solidity, C#, JavaScript, C++, C#.NET, Python, C, Assembly, SQL, TypeScript, C++11, Rust, HTML, Embedded C++, Go, Java, Perl, PHP, Haskell, GraphQL, Solidity Assembly, Python 3, MQL5, MQL4, Pine Script
Frameworks
.NET, ASP.NET Core, .NET 4, .NET Core, ASP.NET MVC, ASP.NET, Express.js, Windows Presentation Foundation (WPF), Knockout (Knockout.js), React Native, Unity, Next.js, ZK
Paradigms
RESTful Development, Agile Software Development, Scrum, REST, Design Patterns, Application Architecture, Model View ViewModel (MVVM), Model View Controller (MVC), Kanban, Unit Testing, Microservices, Windows App Development, Object-relational Mapping (ORM), Mobile Development, Event-driven Architecture, Model Context Protocol (MCP), DevOps, Test-driven Development (TDD), Service-oriented Architecture (SOA), Functional Programming, Agile, Penetration Testing, Serverless Architecture
Platforms
Blockchain, Ethereum, Magento, Amazon Web Services (AWS), Blockchain Platforms, Linux, Arduino, Amazon Alexa, Android, iOS, Web, Xamarin, Unix, Windows, Amazon EC2, AWS Lambda, Kubernetes, Google Cloud Platform (GCP), AWS IoT, Docker, Visual Studio Code (VS Code), Jupyter Notebook, Azure, Mobile, Twilio, Medusa, Decentralized Exchanges (DEXs), MetaTrader, cTrader, MetaTrader 5, Microsoft Copilot Studio
Storage
JSON, Microsoft SQL Server, MySQL, PostgreSQL, SQLite, Amazon S3 (AWS S3), Amazon DynamoDB, NoSQL, MongoDB
Industry Expertise
Trading Robots, Banking & Finance, Trading Systems, High-frequency Trading (HFT)
Other
Ethereum Smart Contracts, WebSockets, Software Development, Software Architecture, Complex Problem Solving, Computer Science, Full-stack, Crypto, Architecture, Web 3.0, Back-end, Technical Architecture, Solution Architecture, Blockchain Architecture, Blockchain Development, System Architecture, Systems Engineering, Full-stack Development, Leadership & Coaching, Real-time Data, Back-end Development, Database Schema Design, Escrow, Smart Contracts, SOAP, ESP8266, Internet of Things (IoT), HTTP, eCommerce, Trading, ESP32, Leadership, Technical Leadership, Team Leadership, Lean Project Management, Solana, Non-fungible Tokens (NFT), Token Design, Ethers.js, Decentralized Finance (DeFi), APIs, Blockchain & Cryptocurrency, Cryptocurrency, Algorithms, Rinkeby, Algorithmic Trading, Algorithmic Trading Analysis, IIS, Legacy Software, Windows Services, API Integration, Automated Trading Software, Stock Trading, Stock Analysis, Prediction Markets, Visualization, Data Engineering, Mobile Apps, Decentralized Systems, ERC-20, Fintech, Multithreading, Web Development, Lambda Functions, Enterprise Architecture, Blockchain Design, Large Language Models (LLMs), Artificial Intelligence (AI), AI Agents, Cloud Architecture, Multitenancy, CTO, GitHub Actions, API Backwards Compatibility, Marketplaces, Payment APIs, Single Sign-on (SSO), Agentic Coding, FastAPI, Data Science, Prompt Engineering, Engineering Management, Backlog Management, API Gateways, Anthropic, OpenAI, AI Tools, Financial System Implementation, Startups, AI Programming, AI Architecture, Agentic AI Systems, EventBus, AI Automation, Quantitative Trading, Trading Bots, Quantitative Finance, Serverless, Webhooks, Payments, User Interface (UI), Domain-driven Design (DDD), RESTful Services, Internet Server Application Programming Interface (ISAPI), COM, Embedded Systems, Real-time Operating System (RTOS), Customized Blockchains, Machine Learning, Defect Management, Arbitrage, Futures, Software, CI/CD Pipelines, OpenSea, Bots, DApps, Integration, Amazon RDS, Training, Web Security, Deep Learning, Hedge Funds, Finance, Statistics, Long Short-term Memory (LSTM), Neural Networks, Recurrent Neural Networks (RNNs), Gaming, R&D, Presentations, Web3, Move, Bitcoin, Cloud, WinDev, Ethereum Virtual Machine (EVM), Cryptocurrency Wallets, Jupiter, Technical Design, Backtesting Trading Strategies, Visual Builders, Fractional CTO, TradingView, Cloud Infrastructure, Quantum Computing, Cargo, Agentic AI, AI Agent Orchestration, Distributed Systems, Observability, Retrieval-augmented Generation (RAG), Open Banking, Backtesting, SaaS, Low-latency Software, Workflow Automation, Quantitative Modeling
Collaboration That Works
How to Work with Toptal
Toptal matches you directly with global industry experts from our network in hours—not weeks or months.
1
Share your needs
Discuss your requirements and refine your scope in a call with a Toptal domain expert.
2
Choose your talent
Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.
3
Start your risk-free talent trial
Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.
Top talent is in high demand.
Start hiring