Hire the Best RSpec Specialists
in Ukraine

With a proven track record as a Full-Stack Developer, Team Lead, and Project Manager at previous companies, I specialize in transforming ideas into fully functional, scalable solutions. My expertise spans the entire development lifecycle - from initial requirements gathering and solution architecture to development, deployment, and DevOps management. Technical Expertise: Backend Development: Ruby on Rails specialist with deep experience building robust, maintainable server-side applications Frontend Development: Proficient in React.js, creating intuitive and responsive user interfaces DevOps: Skilled in deployment pipelines, server configuration, and infrastructure management Full-Stack Architecture: Expert in designing comprehensive solutions that seamlessly integrate frontend and backend systems Leadership & Project Management: I've successfully led cross-functional development teams, managing projects for prominent US-based companies. My approach combines technical excellence with strong communication skills, ensuring stakeholder satisfaction and timely delivery of high-quality solutions. What Sets Me Apart: End-to-end solution development from concept to production. Strong problem-solving abilities and architectural design skills. Experience collaborating directly with clients to understand and exceed their expectations. Proven ability to optimize development workflows and improve team efficiency. Whether you need a complete solution built from scratch or expert guidance on your existing project, I bring the technical skills and leadership experience to drive your success.

Ruby on Rails and Vue.js full-stack developer with 8+ years of experience building SaaS platforms, marketplaces, CRM systems, and healthcare applications from scratch. I’ve shipped production systems handling 1M+ monthly transactions, built a pharma analytics platform used by enterprise B2B clients for over 6 years, and delivered Vue.js and Node.js applications for clients across the US, EU, and UK. 🧠 Backend: Ruby on Rails, Ruby, REST APIs, GraphQL, PostgreSQL, MySQL, Redis, Sidekiq, Apache Kafka, JWT, OAuth2, RSpec (90%+ test coverage), Capybara, Swagger 🎨 Frontend: Vue.js, Vue 3, Nuxt.js, Vuex, Pinia, Vue Router, JavaScript, TypeScript, Tailwind CSS, Hotwire, Stimulus, WebSockets, Stripe integrations ⚙️ Infrastructure: Docker, GitHub Actions, AWS S3, Azure, Heroku, Nginx, Capistrano, CI/CD pipelines What this looks like in practice: → Built and maintained REST and GraphQL APIs consumed by Vue.js SPAs with clean architecture, versioning, and full documentation → Optimized complex PostgreSQL queries, improving performance in systems with 1M+ monthly transactions → Migrated CI/CD pipelines from CircleCI to GitHub Actions, reducing costs while maintaining production stability → Implemented Kafka-based event streaming and optimized data flows in microservice-based systems → Integrated Stripe payments and real-time WebSocket features in Vue.js and Node.js / NestJS applications → Refactored and extended legacy Ruby on Rails systems without breaking existing functionality → Maintained 90%+ test coverage using RSpec and Capybara in production-grade systems How I work: I communicate clearly from day one, define scope before development starts, identify risks early, and keep progress transparent throughout the project. I’ve worked both independently on full-stack products and in distributed teams with async workflows. Looking for a Ruby on Rails or Vue.js developer who delivers reliable production systems, not just code commits? Let’s talk.

⚡𝗥𝘂𝗯𝘆 𝗼𝗻 𝗥𝗮𝗶𝗹𝘀 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗲𝗿 𝗮𝗻𝗱 𝗥𝗲𝗮𝗰𝘁 𝗡𝗼𝗱𝗲.𝗷𝘀 𝗙𝘂𝗹𝗹-𝗦𝘁𝗮𝗰𝗸 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗲𝗿 · 𝟭𝟬𝟬% 𝗝𝗦𝗦 · 𝟴+ 𝘆𝗿𝘀 · 🛡️𝗟𝗶𝗳𝗲𝘁𝗶𝗺𝗲 𝗰𝗼𝗱𝗲 𝘄𝗮𝗿𝗿𝗮𝗻𝘁𝘆. Clients come to me when the product has real complexity - payment flows, multi-role systems, third-party integrations, data-heavy architectures that hold up for years. ✅ 𝗖𝗹𝗶𝗰𝗸 𝗛𝗶𝗿𝗲 𝗼𝗿 𝗜𝗻𝘃𝗶𝘁𝗲 to work with a Node.js Full-Stack Developer who owns the architecture, not just the tickets. 🎯 𝗪𝗛𝗔𝗧 𝗬𝗢𝗨 𝗚𝗘𝗧 ✔️ As a Node.js Full-Stack Developer - full ownership from architecture to deployment. React, Node.js, TypeScript, PostgreSQL, Redis, REST API, Docker, AWS. Clean, documented code. ✔️ As a Full-Stack Web Development React Node specialist - end-to-end SaaS platforms, payment integrations (Stripe, Xero), multi-role admin panels, Elasticsearch reporting. 40-60% faster delivery than split-role teams. ✔️ As a Ruby on Rails Developer - Rails 4-7.1 codebases, monolith upgrades, RSpec-covered backends, Sidekiq async. 8+ years, 15+ production systems shipped. ✔️ As a Node.js Full-Stack and Ruby on Rails Developer React engineer - Next.js, React, TypeScript paired with Node.js or Rails. Full-Stack Web Development React Node delivery across FinTech, EdTech, B2B SaaS. 🔥 𝗦𝗢𝗠𝗘 𝗣𝗥𝗢𝗝𝗘𝗖𝗧𝗦 ✔️ Greek Capital (USA) - accounting + CRM SaaS, Elasticsearch reporting, automated workflows. Ruby on Rails Developer · Full-Stack Web Development React Node. Ongoing since 2017 ($100-250k). ✔️ Roi (Norway) - finance PWA: Stripe, asset tracking, investment calculator. React Node.js Full-Stack · Ruby on Rails Developer React · TypeScript. ✔️ MilkMind (France) - high-load EdTech marketplace, AI integration, video, Stripe. Node.js Full-Stack Developer · Ruby on Rails Developer React · Next.js. ✔️ Sket (Belgium) - LegalTech SaaS: contract automation, blockchain. Ruby on Rails Developer · React Node.js Full-Stack · RSpec. ✔️ H&P Builder (USA) - EHR product, multi-level admin. Full-Stack Web Development React Node · Node.js Full-Stack Developer. 🚀 𝗪𝗛𝗘𝗥𝗘 𝗜 𝗗𝗘𝗟𝗜𝗩𝗘𝗥 ✔️ FinTech SaaS - as a Node.js Full-Stack Developer and Ruby on Rails Developer: payment integrations, credit management, accounting platforms. US, UK, Nordics. 8+ years, zero payment flow failures. ✔️ EdTech & marketplaces - Full-Stack Web Development React Node and React Node.js Full-Stack: high-load architecture, AI integration, video delivery, subscription logic. 30-50% better scalability. ✔️ LegalTech & compliance - Ruby on Rails Developer React and React Node.js Full-Stack: blockchain, document automation, audit-trail data flows for EU-market compliance SaaS. ✔️ HealthTech & EHR - Node.js Full-Stack Developer and Full-Stack Web Development React Node: secure document generation, recommendation logic, HIPAA-aware. ✔️ B2B SaaS - Ruby on Rails Developer, Node.js Full-Stack Developer, Full-Stack Web Development React Node: permission layers, file management, long-term codebase ownership. 🏆 𝗜𝗡𝗗𝗨𝗦𝗧𝗥𝗬 𝗩𝗘𝗥𝗧𝗜𝗖𝗔𝗟𝗦 ✔️ FinTech - Node.js Full-Stack Developer and Ruby on Rails Developer: Stripe, Xero, credit SaaS. Zero payment errors across 8 years. ✔️ EdTech - Full-Stack Web Development React Node and React Node.js Full-Stack: AI-powered, high-load marketplace platforms. ✔️ LegalTech - Ruby on Rails Developer and Ruby on Rails Developer React: smart contracts, document automation, blockchain. ✔️ HealthTech - React Node.js Full-Stack and Full-Stack Web Development React Node: EHR, secure data, recommendation logic. ✔️ B2B SaaS - Node.js Full-Stack Developer: Ruby on Rails Developer React architecture, full ownership. ⚒️ 𝗛𝗢𝗪 𝗜 𝗕𝗨𝗜𝗟𝗗 ✔️ Core - Node.js Full-Stack Developer and Ruby on Rails Developer: Node.js, ExpressJS, Ruby on Rails (4-7.1), JavaScript, TypeScript, React, Next.js, Vue.js, PostgreSQL, Redis, Docker, AWS, REST API, RSpec. ✔️ Frontend - Full-Stack Web Development React Node: React, TypeScript, HTML, HTML5, CSS, CSS 3, Bootstrap, Tailwind CSS, jQuery, Web Design, Mobile App Development. ✔️ Backend - React Node.js Full-Stack builds: ExpressJS, MongoDB, MySQL, SQL, PHP, Laravel, CodeIgniter, Python, API Integration, API, Database Architecture, Software Architecture & Design, Agile Software Development. ✔️ Ecosystem: React Native, Angular, AngularJS, WordPress, WooCommerce, Shopify, iOS Development, Android App Development, Git, Software Development, Software Debugging, Product Development, Search Engine Optimization. ✔️ Creative & extended: Graphic Design, Adobe Photoshop, Adobe Illustrator, Web Application, Software Design, Desktop Application, Data Entry, Ruby, RSpec, PostgreSQL. 🔹 Node.js Full-Stack Developer · Full-Stack Web Development React Node · React Node.js Full-Stack · Ruby on Rails Developer - lifetime warranty on every line of code. 🔹 Ruby on Rails Developer React · UTC+2 · async-friendly Building a product? 👉 Message and let me support your way on a risk-free way..

I build and scale Rails-backed SaaS products, from early MVP to multi-tenant platforms handling real production load. And with over 5 years experience in AI/ML, and prediction/trading field, I developed several prediction models for sports betting and stock trading. Most of my clients come to me with one of three problems: they need a clean API and product built from scratch, their existing Rails app has gotten slow and messy, or they are scaling up and the current architecture will not hold. I have handled all three. 🚀What I have shipped: ▪ Multi-tenant SaaS platforms with Rails API and React frontends (role-based access, subdomain isolation, per-tenant data scoping) ▪ Stripe billing integrations including subscription plans, usage-based billing, metered billing, webhook handling, and dunning flows ▪ API performance turnarounds: cut p95 response times from 900ms to under 150ms through query optimization, N+1 elimination, and Redis caching ▪ PostgreSQL schema design and query optimization for datasets at scale (100k to 10M+ rows) ▪ Background job systems with Sidekiq including scheduled jobs, retries, priority queues, and dead-letter handling ▪ OAuth2 and JWT auth systems, including third-party SSO integrations ▪ Internal tooling and admin dashboards used daily by ops and support teams 🛠️Tech I work with daily: ▪ AI/ML: Python, PyTorch, TensorFlow, scikit-learn, XGBoost, LIghtGBM, Pandas, NumPy, OpenCV ▪ Backend: Ruby on Rails, PostgreSQL, Redis, Sidekiq, RSpec ▪ Frontend: React, Next.js, TypeScript, Tailwind CSS ▪ APIs: REST, GraphQL ▪ Infra: AWS (EC2, RDS, S3, SQS), Docker, GitHub Actions CI/CD ▪ Rust available for performance-critical services when Rails is not the right tool 🤝How I work: I give you a clear plan before writing a line of code. I ask questions upfront so there are no surprises mid-project. You will get clean, documented, production-ready code and not a prototype you have to rewrite in six months. If you are building a SaaS product, scaling an existing one, or need a Rails specialist who understands the full stack, send me a message. I will take a look at what you are building and tell you exactly how I would approach it.

I am a senior EMV L3 certification and payment integration consultant with 10+ years of hands-on experience in POS, SoftPOS and ATM solutions. I have delivered 50+ successful Visa, Mastercard MTIP, JCB, Amex and UnionPay certifications for POS/ATM vendors, acquiring banks and processors across Europe, the Middle East and Asia. My core expertise includes: • EMV Level 3 certification (Retail & Cash) • POS, SoftPOS (CPoC / MPoC) and ATM integrations • ISO8583 transaction flows and payment debugging • Processor-side integrations (Tieto, CompassPlus, Way4, SmartVista, UPC, MADA and D8-based processors) • UL / FIME certification labs and scheme simulators I regularly work with product and engineering teams at the stages where certification, scheme compliance or complex payment issues need to be resolved efficiently. Available for contract, consulting or full-time engagements. Remote.

Ready to dive into your data deeply Make data analysis and predictive modelling Marketing and business domains are preferred Proficient in customer and investments analytics ✅ EXPERT-VETTED TOP 1% ON UPWORK 🚻 Customers and growth analytics Calculation different customer KPI like LTV Segmenting customers by using the RFM method Customers cohorts analysis to detect churn Scoring customer and revenue churn risks Predicting dates and prices of future orders Modeling prices and revenue flow scenarios Analyzing user behavior on social media 🛒 Products and inventory analytics Forecasting stock-out events to minimize lost of sales Planning assortment based on ABC & XYZ analysis Assessing product competitiveness on the market Market basket analysis based on association rules Product sentiment analysis based on social media data 🏦 Venture capital investment analytics Deep understanding of crunchbase data source Scoring startups' success, multiples, and time of exit Startup market analysis and trends insights Modelling investment deals processes Design due diligence recommendations 📶 Trading analytics Designing and verifying trading strategies Modelling reflexive behavior strategies Recognizing threat patterns in trading data Detecting anomalies and outliers in trading data Managing trading deals and assessing associated risks Assessing fraud risks in trading and investment activities Algorithmic trading strategies design for crypto market 🚀 Google Analytics Defining click-through-rate drivers Assessment listings search sort relevance Scoring and ranking website users' engagement Calculations of normalized discounted cumulative gain 🧪 Clinical Trials Analytics Design R Shiny dashboards for analytical results reporting Redesign legacy R and R Shiny code to have more robust apps TECH STACK 🔧 Core Languages Python (primary) – ML systems, data engineering, APIs, AI and LLM R (advanced) – R Shiny apps, analytics, reporting, statistical modeling SQL (expert) – 20+ years, complex analytics & data modeling 🎛 Data Science & Machine Learning Data analysis: tidyverse, data.table, lubridate Modeling: tidymodels, caret, mlr3, parsnip, broom Tree-based models: ranger, randomForest, xgboost, catboost Time series: forecast, prophet, tidyverts, xts, zoo NLP: tidytext, quanteda, sentimentr, stm Quant finance: quantmod, quantstrat Pharma analytics: pharmaverse, rtables, admital, tidytlg 👨‍💻 Data Apps, APIs & Reporting Dashboards: shiny, shinydashboard, bslib, shinyjs App frameworks: golem, rhino, teal Tables: DT, reactable, gt, flextable Reporting: RMarkdown, bookdown, LaTeX Auth: shinymanager, shinyauthr Mobile apps: shinyMobile APIs: plumber 💾 Data Engineering & Storage Databases: RMySQL, RODBC, bigrquery Cloud & formats: aws.s3, jsonlite, feather, openxlsx Distributed: sparklyr, SparkR, h2o Platforms: Databricks, Snowflake, Palantir Foundry, AWS 📶 AI, LLMs & MLOps LLM apps: ellmer, querychat, shinychat,mini007 Shared: Experiment tracking: MLflow 🤹 Visualization Core: ggplot2, ggpubr, ggmap Networks: igraph, ggnetwork, geomnet Hierarchies: treemap, data.tree JS integrations (via R) plotly.js, d3.js, highcharts, leaflet, networkD3 ⚙️ Software Engineering Packaging: devtools, renv, packrat Performance: Rcpp, RcppParallel, microbenchmark Parallel computing: foreach, doParallel ⏱️ Trading & Quant Systems Research & backtesting: quantmod, quantstrat