Hi there! My name is Sally Peck. Tech Stack: - Delphi | VCL | FMX | FastReports | DevExpress (Reference: CodePartners Pty Ltd). - C# | WPF | WinForms - Java Spring - Add-in-Express Team member (Outlook, Word, and Excel Add-in development) - CI/Build environment - Coding support | InstallShield | WIX Please see my happy customers and high ratings below.

I’m a Full-Stack Developer focused on Java and Spring Boot and I also work hands on with Shopify theme customization. I build and maintain storefronts with Liquid sections layout and UX improvements and performance focused fixes. I have several years of experience building web applications and microservices including REST APIs database integration and smooth backend frontend interaction. I like writing clean maintainable code and keeping systems reliable and scalable. I’ve worked across finance travel and e commerce and I adapt quickly. Clear communication and reliable delivery are always my priorities.

Data Engineering | Cloud Solutions (AWS/GCP/Azure) | Full Stack Java & Python Backend Development | ETL Pipelines | Spring Boot | SQL Performance Tuning | Apache Hadoop & Spark, Apache Kafka | Snowflake | dbt | Enterprise Backend Systems I don't just write code, I architect & build systems that process millions of records, reduce company costs, and stay alive at scale. I am a 𝗨𝗦-𝗯𝗮𝘀𝗲𝗱 𝗦𝗲𝗻𝗶𝗼𝗿 𝗕𝗮𝗰𝗸𝗲𝗻𝗱 𝗮𝗻𝗱 𝗗𝗮𝘁𝗮 𝗘𝗻𝗴𝗶𝗻𝗲𝗲𝗿, 𝗖𝗹𝗼𝘂𝗱 𝗧𝗲𝗰𝗵𝗻𝗼𝗹𝗼𝗴𝘆 𝗣𝗿𝗼𝗳𝗲𝘀𝘀𝗶𝗼𝗻𝗮𝗹 𝘄𝗶𝘁𝗵 𝗼𝘃𝗲𝗿 𝟴 𝘆𝗲𝗮𝗿𝘀 𝗼𝗳 𝗲𝗻𝘁𝗲𝗿𝗽𝗿𝗶𝘀𝗲-𝗹𝗲𝘃𝗲𝗹 𝗲𝘅𝗽𝗲𝗿𝗶𝗲𝗻𝗰𝗲 building high-performance systems for Fortune 500 companies, including JPMorgan Chase and Ford Motor Company. I specialize in designing scalable backend microservices, optimizing slow databases, and architecting heavy big data pipelines that process millions of records without downtime. ⚡ 𝗦𝗘𝗥𝗩𝗜𝗖𝗘𝗦 & 𝗦𝗧𝗔𝗖𝗞 ◆ Data Engineering & ETL Apache Spark, Apache Kafka, Apache Hadoop, Apache Beam, Apache Hive, Apache Airflow, GCP Dataflow, AWS Glue, dbt, SSIS, Talend, Snowflake, BigQuery, Spring Batch, Spring Cloud Dataflow, Data Ingestion Pipelines, Data Warehouse Design ◆ Cloud & DevOps GCP (Cloud Run, Cloud Functions, BigQuery, Pub/Sub, GKE, Dataflow) AWS (Lambda, EC2, S3, RDS, Redshift, EKS, CloudWatch, CloudFormation) Azure (AKS, Sentinel, Defender for Cloud, DevOps, Landing Zones) Terraform, Kubernetes, Docker, GitHub Actions, Jenkins, Tekton, Azure DevOps, Control-M ◆ Database & Administration PostgreSQL, SQL Server, MongoDB, MySQL, Oracle, Redshift, DynamoDB, BigQuery, Redis, Snowflake, SQL Performance Tuning, Schema Design, High Availability (Always On, Failover Clustering, Log Shipping), SSRS Reporting, Backup & Recovery ◆ Backend Development Java (8, 11, 17), Spring Boot, Spring Security, Spring Batch, Spring Cloud Dataflow, Hibernate, JPA, JWT Authentication, Microservices Architecture, Multi-threading, Python, FastAPI, Django, Flask, Node.js, NestJS, TypeScript ◆ API & Integrations RESTful APIs, GraphQL, gRPC, WebSockets, Apigee, Swagger/OpenAPI, Payment Gateways, Google APIs, Power BI, Qlik Sense, Open Banking Connectors, Active Directory, ADFS, Zapier, Stitch ◆ Full Stack Development React.js, Next.js, Node.js, Redux, TypeScript, Tailwind CSS, Angular ◆ Testing & Monitoring JUnit, Mockito, MockMVC, Jest, TDD, Integration Testing, Grafana, Splunk, GCP Cloud Monitoring, Azure Sentinel, Webex Alerting, Legacy System Cloud Migration ◆ AI & Developer Tools Claude Code, Cursor, OpenAI Codex, AI/ML Pipeline Integration, LLM-based Workflows, Intelligent Automation 📌 𝗥𝗘𝗦𝗨𝗟𝗧𝗦 𝗜'𝗩𝗘 𝗗𝗘𝗟𝗜𝗩𝗘𝗥𝗘𝗗 ▸ Built core credit card banking microservices at 𝗝𝗣𝗠𝗼𝗿𝗴𝗮𝗻 𝗖𝗵𝗮𝘀𝗲 handling millions of daily transactions ▸ Architected GCP Dataflow pipelines at 𝗙𝗼𝗿𝗱 𝗠𝗼𝘁𝗼𝗿 𝗖𝗼𝗺𝗽𝗮𝗻𝘆 processing millions of records into BigQuery daily ▸ Delivered digital banking platforms powering retail and corporate banking across open banking environments ▸ Reduced ETL data processing times by over 99% for healthcare and enterprise clients ▸ Built mobile backend microservices at 𝗝𝗲𝘁𝗕𝗹𝘂𝗲 𝗔𝗶𝗿𝘄𝗮𝘆𝘀 serving thousands of daily travelers ▸ Administered high-availability database systems for federal government procurement 🏭 𝗜𝗡𝗗𝗨𝗦𝗧𝗥𝗜𝗘𝗦 Fintech · Digital Banking · Healthcare · Government · Automotive · Enterprise SaaS · Education · E-commerce · Travel & Hospitality · Open Banking ✅ 𝗣𝗘𝗥𝗙𝗘𝗖𝗧 𝗙𝗜𝗧 I work best with teams who: → Need Java or Python expertise without hand-holding → Have APIs, pipelines, or databases that need fixing or scaling → Are building on AWS, GCP, or Azure and need someone who knows these environments → Want clean maintainable code delivered on time → Need a developer who can also talk to clients and stakeholders professionally I communicate clearly, deliver on time, and bring Fortune 500 engineering standards to every project regardless of size. Ready to build something that scales? Send me a message or 𝗰𝗹𝗶𝗰𝗸 𝗜𝗻𝘃𝗶𝘁𝗲 𝘁𝗼 𝗝𝗼𝗯. I respond within a few minutes. Data Engineer · ETL · Spring Boot · Cloud Architect . Cloud Engineer . Cloud Migration. Azure Enginer . AWS. GCP . Java Developer · Python · Backend Developer · FastAPI · Django · Flask · REST API · GraphQL · Microservices · Apache Kafka. Apache Spark · Apache Airflow · dbt · Snowflake · AWS · GCP · Azure · Terraform · Kubernetes · Docker · PostgreSQL · SQL Server · MongoDB · Node.js · React.js · Full Stack Developer · Cloud Architect · API Integration · Data Pipeline · Data Warehouse · CI/CD · BigQuery · Kafka · Redis ·

Senior Mobile App Developer | iOS, Android , React Native, Flutter | 10+ Years I help startups and companies build high-quality mobile applications for iOS and Android, from MVP to fully scalable production apps. With 10+ years of experience in mobile development, I have built and delivered applications used by thousands of users across different industries including enterprise, consumer apps, and real-time data platforms. I specialize in building reliable, scalable and high-performance mobile apps using modern mobile technologies. ✅ Top Rated Plus Freelancer ✅ 100% Job Success ✅ 10+ Years Mobile Development Experience What I can help you with • React Native cross-platform mobile apps • Native Android apps (Kotlin) • Native iOS apps (Swift) • MVP development for startups • Scaling existing mobile apps • Performance optimization and debugging • API integrations and backend connectivity • App Store & Play Store deployment Technical Expertise Mobile Development React Native Kotlin / Android SDK Swift / iOS SDK Flutter Backend & APIs REST APIs Firebase Node.js backend integration Third-party API integrations Advanced Mobile Features Maps & location services Real-time data & network communication Media processing (video/audio) Bluetooth / NFC / hardware integrations Sensors & activity recognition Third-Party Integrations Facebook Google APIs Amazon services Dropbox Twitter Instagram Types of Applications I Build • Consumer mobile apps • Enterprise mobility solutions • Real-time data applications • Location-based services • Hardware-integrated apps I focus on clean architecture, maintainable code, and long-term scalability. If you're looking for a reliable mobile developer who can take your idea from concept to production, feel free to send me a message or invite me to your project. I look forward to working with you.

Seasoned software engineer specializing in enterprise grade backend development and real-time system integrations in highly regulated environments. Former engineering lead at CHECK24 - Germany’s largest comparison platform. From concept to post-launch, I stay hands-on while guiding teams and stakeholders. KEY PROJECTS • Real Time Financial Integrations - 15+ bank integrations for real time credit-card approvals. • Digital Identity Verification - video-KYC and qualified-signature workflow with full state tracking. • Secure Document Transfer - modular, encrypted exchange of sensitive bank files to third parties. • ML Credit Card Approval Prediction - led R&D and production rollout of custom approval likelihood model. • Monolith to Microservices - extracted critical domains into independent services with zero downtime. Whether you need a robust, secure and scalable architecture that’s ready for growth or want to integrate AI capabilities into your existing system - I’m here to help you.

Backend developer focused on building and improving real-world applications using Java and Spring Boot. I work mainly on backend development, designing and implementing REST APIs, handling data flows, and working with SQL databases such as PostgreSQL. Currently, I am working in a SAP-oriented environment, contributing to business applications and internal systems. My work involves backend development, database handling, and supporting real processes such as equipment control and invoice integration. What I can help you with: - Build and maintain REST APIs using Spring Boot - Debug and improve existing backend systems - Design database structures and write efficient SQL queries - Integrate backend services with frontend applications - Work on real-world business logic and data-driven systems I focus on writing clean, maintainable code and adapting quickly to existing projects. If you need someone reliable to support your backend or help improve your system step by step, I’d be happy to help.

🏆 Top Rated Web & Mobile App Developer | SaaS & AI Expert | Flutter | iOS | Android | Node.js | React Native | AI, and cloud solutions for startups 🎖️ 20+ Apps Successfully Launched 🌟 15+ Long-Term Client Relationships 💡 Built to Scale & Grow Your Business 10+ years of experience building scalable web, mobile, AI, and cloud solutions for startups, SaaS companies, and growing businesses. I don't just develop apps - I help turn ideas into production-ready products that scale. From MVP development to enterprise-level systems, I handle the complete lifecycle: architecture, development, deployment, optimization, and long-term support. Whether you need a high-performance mobile app, AI-powered platform, SaaS product, automation system, or modern web application, I can help you build it efficiently and professionally. 💡 What I Specialize In 📱 Mobile App Development • Flutter, React Native • Native iOS (Swift, SwiftUI) • Native Android (Kotlin, Java) • Cross-platform apps with clean, scalable architecture 🌐 Full-Stack Web Development • React.js, Next.js, Vue.js, Angular, Svelte • Node.js (Express, NestJS) • Python (Django, Flask, FastAPI) • Laravel, Java Spring, .NET 🤖 AI & Automation • OpenAI / ChatGPT integrations • AI chatbots, AI agents, RAG systems • LangChain, LlamaIndex, Vector Databases • OCR, NLP, automation workflows • TensorFlow, Machine Learning solutions 🔗 Web3 & Blockchain • Smart Contracts (Solidity) • NFT Platforms • Blockchain integrations • Solana & Ethereum ecosystem development 🕷 Web Scraping & Reverse Engineering • Puppeteer, Selenium, Scrapy, BeautifulSoup • Data extraction & browser automation • Anti-bot handling & workflow automation ☁️ Backend, APIs & Cloud • REST APIs & GraphQL • PostgreSQL, MySQL, MongoDB, Redis, Firebase • AWS, GCP, Docker, Kubernetes • CI/CD pipelines & scalable cloud deployment ⚡ Features I Frequently Build • Real-time chat systems • Payment integrations (Stripe, PayPal) • Push notifications • Maps & geolocation • Authentication systems (OAuth, JWT, Social Login) • SaaS dashboards & admin panels 💼 Why Clients Work With Me ✔ Clean, scalable, production-ready code ✔ Fast communication & reliable delivery ✔ Strong architecture & problem-solving skills ✔ Startup speed with long-term engineering mindset ✔ Full ownership from idea to deployment ✔ Long-term support & maintenance I focus on building solutions that are not only functional, but also scalable, secure, and built for real business growth. If you're looking for a developer who can take ownership of your project and deliver high-quality results without unnecessary complexity, let’s connect. 📩 Send me a message and let’s discuss your project.--------------------------------------------------------------------------------------------------------------------- Core Roles: Mobile App Developer, AI Engineer, Flutter Developer, iOS Developer, Android Developer, RAG Developer, AI Chatbot Developer, Machine Learning Engineer, Full Stack Developer, Mobile Architect. Mobile Tech: Swift, Kotlin, Dart, SwiftUI, Objective-C, Java, Firebase Integration, Mobile UI/UX Design, Custom Mobile Solutions, Native iOS, Native Android, Cross-Platform Development, Secure App Development, MVP Development, In-App Purchase, Payment Gateway Integration, Google Maps API, Push Notifications. AI & Backend Tech: Python, FastAPI, LangChain, LlamaIndex, OpenAI API, GPT-4, Llama 3, Vector Database, Pinecone, Weaviate, Generative AI, LLM Fine-Tuning, AI Agents, NLP, Computer Vision, Chatbot Development, Automation, Data Engineering, Backend API, AWS, Docker. Process & Optimization: Application Requirement Analysis, Code Optimization, Performance Tuning, App Store Launch, Scalability App, Maintenance App, Debugging Mobile App, Strategy App Development, Cloud Messaging, Remote Mobile Developer.

🚀 Full-Stack Web App Developer | React • Node.js • TypeScript | Atlassian Integration Support I'm a full-stack developer with over 5 years of experience building scalable, high-performance web applications for clients across the US and Europe. My core focus is on developing modern SaaS platforms, custom dashboards, and business automation tools using React, Node.js, and TypeScript. 🛠️ Core Tech Stack: Frontend: React, Redux, Tailwind CSS Backend: Node.js (Express, NestJS), Python (Django), Java (Spring Boot) Cloud & DevOps: AWS, GCP, Docker, GitHub Actions Databases: PostgreSQL, MongoDB, MySQL Beyond hands-on development, I’ve also led engineering teams and managed full-cycle project delivery—from planning and architecture to deployment. 🔧 Atlassian Development: I’ve worked extensively with the Atlassian ecosystem, building custom Jira and Confluence apps, automating workflows, and integrating with external systems using Atlassian Forge, Connect, and REST APIs. I also support CI/CD pipelines that combine Jira, Bitbucket, and GitHub Actions. If you're looking for a React SaaS developer who also understands how to extend and integrate Jira/Confluence into your business processes, I’d love to help.

If you ask ChatGPT or Gemini "Vadim Kolchanov is", you will get a summary about a Senior Backend Developer who builds high-load systems and contributes to Web3 open-source. I am a Senior Backend Engineer (Java/Kotlin) with 6+ years of experience designing scalable enterprise applications. With a background in Fundamental Physics, I approach software architecture with strict logic and algorithmic precision. Whether you need to build a robust microservice architecture from scratch, optimize a struggling backend, or integrate Web3 features, I can help. TECHNICAL SKILLS Languages: Kotlin, Java (up to 21) Frameworks: Spring Boot 2.7 / 3.x, Spring Cloud, WebFlux, Security, Data JPA, Hibernate Databases: Oracle, PostgreSQL, Redis, MongoDB, ClickHouse Message Brokers: Kafka, RabbitMQ DevOps: Kubernetes, Docker, GitLab CI, Elasticsearch, Kibana, Grafana Testing: JUnit 5, Mockito - unit & integration coverage Other: Liquibase, Gradle, Maven, Firebase Cloud Messaging In my recent role, I developed the backend for a large digital ecosystem with a gateway request rate exceeding 100,000 requests per minute. I designed and delivered multiple core services from scratch and migrated critical infrastructure to newer Spring Boot versions, sharing the process through internal engineering articles. By leveraging Kotlin Coroutines, request parallelization, and SQL query optimization, I accelerated critical API response times by four times, reducing latency from 800ms to 200ms. I also resolved critical race conditions in Redis to stabilize cache performance under heavy load and implemented the iterative Ramer-Douglas-Peucker algorithm to optimize geo-track data transmission. Outside of enterprise development, I am heavily invested in open-source and Web3. I created a popular Kotlin client for the Polymarket API used for trading bots, encapsulating complex cryptographic logic. Let's discuss your backend needs.

I help startups and growing businesses design, build, and scale high-performance web and mobile applications—from MVP to production—using modern, reliable technologies and clean architecture. With 5+ years of hands-on experience and a Top Rated Upwork profile with 100% Job Success, I specialize in delivering end-to-end solutions that are maintainable, secure, and aligned with real business goals—not just code. 🔹 What I Can Help You With Full-Stack Web Development: SaaS platforms, dashboards, APIs, and business systems Backend Engineering: Scalable APIs, system design, performance optimization Mobile App Development: Cross-platform apps with React Native AI Integration: Chatbots, automation, recommendations, and AI-powered features Code Refactoring & Optimization: Improve speed, stability, and maintainability 🔹 Core Technologies Frontend: React, Next.js, HTML, CSS, Tailwind, Bootstrap Backend: Node.js, Express, Java (Spring Boot), PHP (Laravel) Mobile: React Native AI & Automation: OpenAI, Hugging Face, NLP workflows Cloud & DevOps: AWS, Linux servers, CI/CD, cPanel 🔹 How I Work Clear and consistent communication Strong focus on clean code and scalable architecture Business-oriented mindset (I think beyond “just development”) Reliable delivery with attention to performance and security I’ve successfully delivered solutions across fintech, e-commerce, content platforms, and education, collaborating with clients to turn complex ideas into practical, user-friendly products. 🔹 Let’s Work Together If you’re looking for a reliable senior full stack developer who can take ownership of your project and deliver real value, feel free to message me. I’m happy to review your requirements, existing code, or product idea and suggest the best way forward.