Yaroslav Protsenko

About

Experience

1. .NET Developer · Freelance

   Feb 2026 — Present

   9 mos

   • Prototypes and application development for clients

     Before committing to full development, clients asked for quick prototypes to demo the idea and check that it was feasible. I built these prototypes with Claude Code on tight deadlines, then worked on developing the applications themselves in .NET. Project details are confidential.

     • Fast prototypes with Claude Code: interactive web demos and a Flutter mobile app with on-device face detection (Google ML Kit).
     • ASP.NET Core (.NET 10) backend with separate business logic and data access layers: EF Core and PostgreSQL, Hangfire background jobs, JWT authentication, OData, Swagger.
     • Claude API (Anthropic) integration in the .NET backend, HTML parsing (AngleSharp) and image processing (ImageSharp).
     • React frontend with maps (Leaflet) and localisation (i18next), deployed with Docker.
     • C#
     • .NET 10
     • ASP.NET Core
     • EF Core
     • PostgreSQL
     • Hangfire
     • Claude API
     • React
     • Leaflet
     • Docker
     • Flutter
     • Claude Code

   • Extending clients' CRM systems

     Added features to several CRM systems, from access rules and tasks to a voice AI agent integration.

     • Vapi integration (voice AI agents): leads go out to automated calling campaigns, a Hangfire background job collects every call — outcome, transcript, recording, answers — and maps the agent's answers onto lead fields; do-not-call blocks the agent for that lead.
     • Tasks in the CRM and field-level permissions by role: which fields each role can see.
     • Desk-based visibility for clients and projects, client and project cards with calculated fields.
     • A knowledge base inside the CRM: page tree, Markdown, trash, images.
     • APIs with OData filtering and per-user access rules, unit tests.
     • C#
     • .NET 9/10
     • ASP.NET Core
     • EF Core
     • PostgreSQL
     • Hangfire
     • OData
     • Vapi API
     • xUnit

   • CRM and backend services for an online game

     A CRM for a game platform: player accounts, game sessions and notifications, plus a secured channel the game's own backend uses to talk to the CRM.

     • Player accounts: sign-up, OAuth sign-in, device sessions with refresh tokens, nicknames and avatars, soft delete and full data erasure on request, a consent audit trail.
     • A service channel for the game backend: API key and HMAC signature authentication bound to the request method and path.
     • Idempotent game session sync and a game registry with per-game session schemas — onboarded several waves of new games.
     • Durable notifications: idempotent inbox, campaigns, retention.
     • For staff: roles and permissions, OData grids of players and sessions, request logging with secrets masked.
     • C#
     • .NET 9
     • ASP.NET Core
     • EF Core
     • PostgreSQL
     • Hangfire
     • OData
     • JWT
     • OAuth
     • HMAC

   • AI-powered news aggregator

     Jun 2026 — Sep 2026

     4 mos

     A platform that gathers news from many sources, brings together coverage of the same event from different outlets and shows where they agree and where they differ. I built the backend.

     • Ingesting content from RSS, websites and Telegram channels, extracting article text and filtering out copies.
     • A Claude-based AI pipeline: distilling facts, grouping coverage of one event across sources, scoring importance and auto-publishing the most significant stories; prompt caching to keep costs down.
     • Hybrid site search: semantic (vector embeddings), keyword and freshness-aware.
     • Feed translation through LLMs, including Qwen.
     • Reader accounts: sign-up, Telegram sign-in, device sessions, favourites; moderation of the public feed and reader management in the admin panel.
     • C#
     • .NET 10
     • ASP.NET Core
     • EF Core
     • PostgreSQL
     • Claude API
     • Qwen
     • Embeddings
     • Hangfire
     • Quartz
     • WTelegramClient

   • Telegram Mini Apps and bots

     Aug 2026 — Sep 2026

     2 mos

     Several products that live inside Telegram, from a storefront to a security service.

     • A Telegram storefront: a Mini App with catalogue, cart and orders, a Blazor admin panel and a notification bot.
     • Online booking for services: schedules and slots, bookings, an admin panel — a new business is set up without code changes.
     • A bot that checks attachments in group chats for malware: a static analysis pipeline (file type, hashes and reputation, archive unpacking, obfuscation), ClamAV antivirus, URLhaus link checks and a monitoring dashboard.
     • C#
     • .NET 8/9
     • Telegram.Bot
     • Telegram Mini Apps
     • Blazor
     • React
     • PostgreSQL
     • ClamAV
     • SignalR
     • Docker
     • xUnit

   • AI assistant for Telegram group chats

     A bot built for a client that you add to a group chat: it reads the conversation and steps in when it can help — fact-checking on the web, reminding people of points they missed earlier, and taking over the tedious information hunting. Built on n8n and now running in many chats.

     • An AI agent on Claude (Anthropic) with tools: web search (Tavily), page scraping (Firecrawl), sending chat messages and a dedicated step for thinking through its answer.
     • Handles more than text: voice messages are transcribed (OpenAI), documents are converted and analysed by the model.
     • Two-level memory: conversation history in PostgreSQL plus long-term notes the agent saves, retrieves and deletes on its own.
     • n8n
     • Claude (Anthropic)
     • OpenAI
     • Tavily
     • Firecrawl
     • PostgreSQL
     • Telegram Bot API

   • Client website improvements

     Smaller but regular tasks on client websites.

     • AI translation and rewriting of content via the Claude API on six websites, with handling of timeouts and failed translations.
     • Localisation tooling: finding unused translation keys and deleting them in bulk.
     • Migrating a website's database from MySQL to PostgreSQL.
     • C#
     • .NET
     • Claude API
     • PostgreSQL
     • MySQL

2. .NET Developer · GenieSolutions

   Dec 2021 — Mar 2026

   Ukraine4 yrs 4 mos

   Grew from supporting the company's websites to development work and payment integrations.

   • Paytiko — payment provider integration platform

     Sep 2022 — Mar 2026

     3 yrs 7 mos

     A service that lets businesses connect to multiple payment providers. I was responsible for payment provider integrations and keeping them running.

     • Built 50+ payment provider integrations from scratch, including Stripe, Adyen, Checkout.com, Braintree (PayPal), Worldpay (Google Pay), Amazon Pay, Ebanx, AstroPay, Flutterwave and Zen.
     • A wide range of payment methods: cards, wallets, crypto, buy now, pay later and local methods such as M-Pesa and Przelewy24.
     • The full payment lifecycle: hosted payment pages and direct server-to-server calls, status webhooks, request signing and verification, 3-D Secure, refunds and payouts.
     • Kept teammates' integrations working when providers changed their APIs, including PayPal and Binance Pay.
     • Covered integrations with unit tests.
     • C#
     • .NET
     • ASP.NET Core
     • REST API
     • Webhooks
     • MSTest
     • Moq
     • FluentAssertions

   • Company web projects: support and development

     Dec 2021 — Aug 2022

     9 mos

     Started out supporting the company's websites, then joined development on its other projects before moving to Paytiko.

     • C#
     • .NET

3. PHP/Laravel Developer · Freelance

   Feb 2021 — Dec 2021

   Kharkiv Oblast, Ukraine11 mos

   Contract backend work: helped build the two systems below and supported the client's other projects, investigating and fixing bugs.

   • Paid parking platform

     A paid parking platform made of three apps: a web panel for administrators, a mobile app for drivers and a tablet app for parking attendants. I worked on the backend shared by all three.

     • Admin panel: parking zones drawn on a map point by point, pricing, assigning attendants to zones.
     • Driver app: registered vehicles, parking payments and a subscription that lets the car stay without paying per visit.
     • Attendant app: patrolling and checking parked cars for a paid session or an active subscription.
     • Role-based access for three roles: drivers, attendants and administrators.
     • PHP
     • Laravel
     • MySQL
     • REST API

   • Access control with temperature screening

     An employee access system for any kind of workplace, built during the COVID-19 pandemic: at the entrance a person scans their pass, then steps up to a stand that takes their temperature. I worked on the backend.

     • Every entry is tied to the employee's pass, recording the time and their temperature.
     • Ingesting readings from an STM32-based stand and keeping the full history.
     • Mobile app for employees to see their own entry and temperature history.
     • Admin dashboard with the complete record for every employee: when they came in and at what temperature.
     • PHP
     • Laravel
     • MySQL
     • STM32
     • REST API

Skills

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