.NET Developer

Yaroslav R

Information

Available hours \ week
40 h/w
Seniority level
Middle
Years of experience
5 yrs.
Location
Poland
Nationality
Ukraine
Timezone
(GMT+01:00) Warsaw

Languages

English
Upper-Intermediate (B2)

About

Yaroslav is a Middle .NET Developer with 5+ years of commercial experience building secure, production-grade REST APIs and SaaS backends on Microsoft technologies. He specialises in C#,. NET/.NET Core, ASP.NET Core Web API, Entity Framework, MS SQL Server, Blazor, React, SignalR, gRPC, Docker, and Azure. His backend work covers multi-tenant data isolation, audit logging, API security with OAuth 2.0/OIDC and Duende IdentityServer, reliability patterns such as idempotency and retries, and the gradual migration of legacy monoliths to independently deployable API services. Yaroslav has strong practical AI experience. He designed and built a RAG-based auto-reply platform across Facebook, Instagram, and TikTok with a unified multi-provider abstraction layer over Claude, GPT, and other models, and delivered an AI assistant layer for a flight-booking system in which every AI-initiated operation is executed through validated, controlled backend functions.

Experience

RAG-Based Social Media Auto-Reply System

Backend / AI Engineer

About the Project

Automated reply system for private messages and comments across Facebook, Instagram and TikTok, using Retrieval-Augmented Generation to fetch relevant context and generate accurate, brand-consistent responses.

  • AI
  • Social Media

Responsibilities

– Designed and built an automated reply system for private messages and comments across Facebook, Instagram and TikTok; – Implemented a RAG pipeline with a vector database to retrieve relevant brand context and generate accurate, brand-consistent responses; – Built a unified abstraction layer over multiple AI providers (Claude, GPT and others), enabling easy provider switching and cost optimization; – Developed secure REST API endpoints and webhook handlers for ingesting platform events and delivering generated replies; – Enforced per-brand data isolation so that retrieval and generation never crossed tenant boundaries; – Added logging and audit history for every generated reply, with moderation rules and human approval for sensitive cases; – Implemented retry, rate-limit handling and provider fallback to keep the system reliable under platform API limits;

Skills & technologies

AI Chat for Flight Booking

Backend / AI Integration Developer

About the Project

AI assistant layer for a flight-booking system, integrated with a .NET backend and database through secure REST APIs, DTO validation, and controlled execution of assistant-initiated business operations.

  • Travel
  • AI

Responsibilities

– Integrated AI assistants with the .NET backend and database layer for booking, user, and flight data access; – Implemented REST API endpoints for AI-driven data retrieval and booking interactions; – Restricted AI access to business functions through an allow-listed tool layer, so agents could only execute pre-approved, validated operations; – Designed and validated DTO models using JSON Schema to ensure reliable and structured data exchange; – Configured assistant interaction flows using Assistants API threads, messages, and tools; – Ensured secure and controlled execution of AI-initiated operations through backend validation logic; – Added audit logging of every AI-initiated booking action, including inputs, resolved parameters and outcome; – Worked with Azure OpenAI, OpenAI GPT-4, and Perplexity to improve reliability and response quality;

Skills & technologies

E-commerce Platform for U.S. Clothing Brand

Full-Stack Developer

About the Project

E-commerce solution for a well-known U.S. clothing brand, focused on backend API functionality, third-party integrations, performance optimization, and Azure-based delivery.

  • Retail
  • E-commerce

Responsibilities

– Developed backend features and supported frontend delivery across Blazor, React, and modern web technologies; – Exposed catalogue, order and customer data through versioned ASP.NET Core REST APIs consumed by the storefront, mobile clients and partner integrations; – Implemented authentication and authorization with OAuth 2.0 / OIDC and scoped API permissions for external consumers; – Designed new backend functionality, maintained existing modules, and presented proposed solutions to the customer; – Set up CI/CD pipelines and created architecture documentation for development and delivery processes; – Collaborated with UI and QA teams, participated in code reviews, and contributed to architecture discussions; – Optimized application code and SQL queries to improve performance, reliability, and troubleshooting efficiency; – Implemented integrations with third-party APIs including payment gateways, e-commerce platforms, and CRM systems;

Transit Map Automation Platform

Full-Stack Developer

About the Project

Cross-platform application using .NET MAUI and ASP.NET Core Web API to automate transit map generation based on mixed-integer programming and geo-data processing.

  • Transportation

Responsibilities

– Developed utilities for importing, optimizing, and formatting geo-data from open data sources; – Split monolithic processing logic into independently deployable containerized backend services communicating over REST; – Designed and optimized backend database architecture, including normalization and performance tuning; – Planned and executed major system updates, module migrations to newer .NET versions, and legacy data transfer scripts; – Set up CI/CD pipelines for Android and backend deployments and contributed to architecture documentation; – Implemented authentication and authorization for the client and backend using Microsoft Azure and MSAL; – Built and tested core backend and client-side functionality across .NET MAUI and Web API modules;

Contacts Management System for Sage Platform

Full-Stack Developer

About the Project

Contacts Management System integrated with the Sage platform, gradually migrated from a legacy ASP.NET MVC monolith towards API services, with role-based access control, tenant isolation and full change traceability.

  • Management

Responsibilities

– Developed backend functionality using ASP.NET MVC and Razor views; – Separated business logic from legacy Razor and Angular interfaces into a dedicated .NET service layer exposed via REST API; – Incrementally migrated modules from the ASP.NET MVC monolith towards independently deployable API services without downtime; – Implemented tenant-level data isolation and audit logging of contact changes to guarantee traceability; – Implemented business logic and reporting using MS SQL Server stored procedures and views; – Maintained and enhanced frontend interactivity using a legacy Angular application; – Ensured compatibility with Sage APIs and the target data model; – Supported role-based access control and user permission management; – Collaborated with stakeholders to gather requirements and deliver reliable production features;