Volodymyr Khrystian

💼 Schoetex IT-Solutions — Full-Stack Developer — Lohr am Main, Germany — On-site

• Enterprise Mail Client (React, PHP/Yii2) — replaced Microsoft Outlook for ~100 employees company-wide; delivered 40+ features across the full mail client lifecycle Show full feature list

  Email Composition & Sending

  • Drafts System (Entwürfe) — auto-save with debounce (2s), save-on-blur, save-on-tab-hide, and save-on-unload; dedicated DB table, editable/listable/deletable
  • Forward Email (Weiterleiten) — forwards with a "WG:" subject prefix; original attachments are copied and re-attached automatically
  • Reply All (Allen antworten) — one-click reply to all recipients (To + CC)
  • Email Attachments — upload, preview, download, and forward; stored per-mail or per-draft/template
  • Email Validation — recipient address validation with inline error highlighting before send
  • BusPro Integration — opens the compose window from an external system with pre-filled To/Subject/Body via query params
  • Email Templates — save and reuse compose presets (To, CC, Subject, Body, Attachments), per employee
  • CC / BCC Support — CC recipients surfaced in the compose toolbar
  • Email Autocomplete — recipient suggestions from the internal address book (debounced 300ms)
  • HTML Rich-Text Editor (TinyMCE) — full WYSIWYG: bold/italic/lists/links/tables/code/word-count/search-replace, image insertion via a CORS proxy
  • Email Signature Management — per-account signature auto-inserted into new compose, reply, forward, and template windows

  Email Management

  • Batch Operations — multi-select emails and apply move, tag, mark read/unread, mark done/undone, or delete across folders in one action
  • Subject Editing (Betreff bearbeiten) — inline subject edit in the viewer, persisted to the DB
  • Email Body Editing — edit a received email's body directly in the viewer and save the modified version
  • Context Menu — right-click menu on mail rows: reply, forward, move, tag, mark read/unread, mark done, download EML, delete
  • EML Download — export any email as a standards-compliant .eml file
  • PDF Export — generate a PDF of an email (with headers) via html2pdf; external images are fetched through a proxy and embedded as base64
  • Trash Folder (Gelöschte) — soft-delete moves emails to Trash; permanent deletion available from there
  • Read / Unread Status — mark individually or in batch, persisted via a DB flag
  • Done / Completed Flag — mark emails "done" individually or in batch, shown as a check-square icon
  • Sent Mail Display — the Sent folder shows the recipient instead of the sender

  UI / UX

  • Minimizable / Resizable Windows — compose/viewer windows are draggable, resizable, maximizable, and minimizable to a taskbar; multiple windows supported with z-index management and tile-to-half-screen layout
  • Resizable Panel Splitter — splitter between folder tree and mail list; sizes persisted in localStorage
  • Browser Notifications — desktop push notifications for new emails while the tab is in the background
  • Folder Unread Counts — badge showing unread-mail count per folder, refreshed on a polling interval

  Search & Filtering

  • Search All Folders — full-text search across all folders at once (including Trash), debounced at 300ms
  • Tag Filtering — filter the mail list by one or more tags, reloading immediately
  • Date Range Filtering — filter emails by a custom date range via a calendar picker
  • Multi-Sort Options — sort by Date, From, or Subject, ascending/descending (6 combinations)

  Tags System

  • Tag Management — create and delete tags per account, shown as colored chips on each email row
  • Tag Synchronization — bidirectional sync of tags with the external mail-fetcher service
  • Tag Import — bulk-import tags from an external system
  • Tag Delete Sync — propagates tag deletions to the mail-fetcher service so they aren't re-created on next sync

  Folder Management

  • Folder Tree (Create / Rename / Move / Delete) — full CRUD on IMAP folders, including drag-to-reorder and soft-delete
  • Folder Position Persistence — per-account folder order saved to the database

  Performance & Backend

  • Async Email Loading — lazy/infinite-scroll loading via a data scroller component
  • Folder Performance Optimization — DB indexes and query-level caching for folder counts/lists
  • Service-Oriented Refactor — a monolithic mail controller split into 7 focused service classes
  • Mail Cleanup Scripts — console commands for automated purging of old emails
  • Database Migrations — schema managed via versioned migrations covering all features

  Infrastructure

  • File Proxy — serves attachments securely, preventing direct filesystem access, and supports CORS image loading for PDF export
  • Multi-Account Support — multiple email accounts per user, each with its own folders, tags, signature, and SMTP config
  • New-Mail Check Interval — configurable polling interval for new-mail detection, persisted per account
  • Folder Sync Command — console command syncing folder structure with the IMAP server / mail-fetcher service

  User Preferences

  • Compact List View — single-line mail list mode (sender address + date/time only), setting persisted in localStorage
  • Panel Background Colors — configurable background color per panel (folder tree, list, viewer), persisted in localStorage
  • Background Inbox Reload — a 30s poll silently checks for new mail; refreshes folder counts and merges new mail into the list when the inbox is open, without disturbing scroll position, open popups, or in-progress edits
• Cruise Booking Platform (PHP/Yii2, TypeScript) — full-stack features across a multi-brand portal: AJAX-driven catalog with SPA-like filtering, dynamic ship page widgets, booking flow features

🚀 Personal Project — Language Learning Platform (krysbot.com) — side project alongside full-time work

• Architected and operate a production language-learning platform as a distributed system: NestJS API gateway, TCP microservice, and a standalone Fastify/Socket.IO realtime service — ~110K lines of TypeScript across 6 applications
• Designed an event-driven backend with Bull/Redis queues and an internal event bus; polyglot persistence: MySQL, MongoDB, ClickHouse (analytics), MinIO/S3
• Built an end-to-end AI voice chat: speech-to-text → streaming LLM → text-to-speech, with Socket.IO streaming and LiveKit realtime audio (Vercel AI SDK, OpenAI)
• Implemented a spaced-repetition engine, YouTube-based lessons, and TTS/STT with multi-provider fallback (AWS Polly/Transcribe, Google Cloud Speech)
• Shipped 4 clients from a shared backend: React/MUI web app, React Native (Expo) mobile app doubling as a Telegram Mini App, admin panel, and a Telegram bot
• Integrated Stripe payments and Google/Apple OAuth
• Operate a self-hosted DevOps platform for the project: Forgejo git server, Woodpecker CI/CD, and a private Docker registry on a home server, connected to the production VPS over Tailscale — push to master triggers build → image push → SSH deploy

⏸ Career Break

• Relocated to Germany; completed VHS German integration course (B1)
• Personal project: Vocabulary Assistant (va.krysbot.com) — Telegram bot, live in production
• Upskilling: Python, FastAPI, React Native, Expo

💼 UVISION/Softum — Senior Fullstack Developer — Remote/Contract — B2B SMS Marketing Platform

• Designed a real-time + batch data ingestion pipeline (Laravel/SQS → NestJS → ClickHouse) handling ~4B records, replacing a legacy MySQL rollup system; consolidated an isolated historical ETL process, establishing a unified central analytics store for the platform
• Cut weekly report load times from ~10s to ~1-2s, monthly from minutes to seconds, and enabled yearly reports that previously froze the dashboard entirely
• Diagnosed campaigns stuck in a locked state under concurrent load — ruled out an SQS visibility-timeout hypothesis, traced the root cause to MySQL index/lock contention, and resolved it via targeted composite-index redesign
• Owned the real-time contact-ingestion system ("live lists"): fixed MySQL–Elasticsearch consistency issues and Elasticsearch scroll-pagination bugs affecting large syncs; added per-campaign TPS rate-limiting to stay within carrier throughput limits

💼 SOS Credit — Senior PHP Developer — Remote/Contract — Fintech (online consumer lending)

• Worked in a regulated fintech domain — owned money-affecting billing logic running daily on every active loan, implemented NBU regulatory reporting and legally-binding qualified e-signature (ESignNki) + BankID identity flows, where errors carry direct financial and legal consequences
• Owned the billing calculation core — commission calculators, balancing triggers and a PostgreSQL stored-procedure router running daily on every active loan
• Built the automated credit-scoring & decisioning pipeline; integrated 3 credit bureaus (UBKI, MBki, PVBki) and led the standalone sos-bki Symfony 4 microservice
• Integrated NBU BankID identification and ESignNki qualified e-signature flow → fully paperless loan agreements
• Refactored the PDF/document pipeline to a queue-based architecture (AMQP + Redis), eliminating timeout failures under load

💼 JBW Soft — Senior Full-Stack Developer — Remote/Contract — Academic-writing SaaS marketplace

• Co-led Symfony 5.4 migration of the legacy Yii2 monolith (59 modules); refactored key domain areas and increased test coverage from ~50% to ~80% — improving deployment stability and reducing regression risk
• Built IP rate-limiting microservice (Symfony / RabbitMQ / Redis) — AMQP consumer processing signup and order events; blocks abusive IPs in Redis via Strategy pattern
• Built HTTP Sender microservice (Node.js / Express) — fire-and-forget async dispatcher decoupling outgoing HTTP calls (Slack alerts, PlagScan, Trustpilot, media conversion) from the main request cycle; automatic retry on failure
• Built Writer Telegram Bot (Node.js / Telegraf / MongoDB) — real-time push notifications cut writer response time from hours to minutes
• Built Reminders microservice (NestJS / Socket.IO / PostgreSQL) — event-driven from the main platform; mutex-style edit locking with real-time WebSocket broadcast to all support staff; RBAC via user groups; cut customer request processing time from ~5 min to ~1 min
• Delivered React + Redux features (RBAC support UI, template management, notification feeds); maintained GitLab CI/CD (PHP CS Fixer, ESLint, Codeception, multi-env Docker)

💼 Finko Finance — Backend Developer — Dnipro, Ukraine — Fintech sector

• PHP / Zend Framework backend for multi-brand microlending platform operating across 5+ countries (Ukraine, Russia, Georgia, Armenia, Jordan)
• Integrated credit bureau APIs (UBKI/BKI), bank card disbursement, BankID identity verification, e-signature
• 85% backend / 15% Vue.js frontend in a team of ~10 during rapid multi-country expansion; platform served tens of thousands of active users with hundreds of daily loan disbursements

💼 Noosphere Ventures (price.ua) — Backend Developer — Dnipro, Ukraine — E-commerce (price comparison)

• Contributed to backend development of a high-traffic price-comparison platform (price.ua — Ukraine's #2, 8.3M+ monthly visits, 11M+ products, 2,000+ partner retailers)
• Participated in building concurrent XML price feed ingestion and parsing pipelines for partner retailers (Gearman → RabbitMQ, MySQL, Sphinx)
• Contributed to merchant tools: TOP-5 auction bidding, contextual advertising, VIP/Selection placements, PhoneView, click statistics, autobudget, competitor price monitoring, store ratings, and brand pages
• Designed the Microsoft SQL Server Data Warehouse schema and built custom PHP ETL pipelines extracting and transforming data from MySQL into MSSQL, feeding an SSAS OLAP cube used by the business analytics team for multidimensional reporting across multiple business dimensions
• Optimized database queries and Sphinx indexes + Redis caching, reducing critical query response times from ~1s to under 100ms on a platform serving millions of daily requests
• Implemented multi-level caching strategies — Redis object cache and full-page caching for high-traffic catalog and product pages — significantly reducing backend load at peak traffic

💼 KTTSoft, Ukraine

• Worked as a PHP developer in outsourcing company.
• Developed and maintained web applications using PHP, MySQL, and JavaScript.
• Developed API for IOs mobile application using Yii framework.
• Developed Magento online store for client from USA (Shop4Seats).

💼 Worked in a different industry (not directly related to current career focus).

🎓 Dnipro National University, Ukraine

Master’s Degree in Engineering.