Backend & Platform Engineer
I'm Wiktor Jeleń, a backend and platform engineer based in Cracow, Poland. I build multi-tenant production systems, infrastructure and security-critical backends, and I wrote PythonMetaTrader5, an open-source library with over 42,000 PyPI downloads.
I design and build backend systems, infrastructure and production-grade platforms.
Multi-tenant automation platform · Lead developer & architect · 03–08.2026 · Architecture & delivery
Problem
An automation platform needs to coordinate external services and AI workflows while keeping each tenant’s data isolated.
Solution
Designed the TypeScript/NestJS backend with Temporal workflow orchestration and PostgreSQL row-level security. Built isolation-leak tests in CI, external-service integrations and a multi-provider AI layer with an evaluation harness.
Stack
Open-source order-execution library · 42,000+ PyPI downloads
Problem
The native Python API for MetaTrader 5 is low-level: raw retcodes, inconsistent data shapes, and no safeguards standing between a strategy and a live account.
Solution
A Python layer over MetaTrader 5 built for algorithmic trading: order normalization, full retcode handling and safeguards that keep execution stable against real capital.
Stack
Trading automation system · Docker image · CI/CD
Problem
TradingView can only fire a plain, unauthenticated HTTP webhook. Anything listening on a guessable URL is eventually found by a scanner — and this endpoint opens positions on a live account.
Solution
FastAPI service translating TradingView alerts into TradeLocker orders, with the webhook path generated as a random secret that is printed once at startup and never again. Shipped as a Docker image built by GitHub Actions.
Stack
Medical University of Silesia platform · 450+ concurrent users
Problem
An anatomy teaching platform had to serve a whole faculty at once, authenticate against the university directory, and stay up through exam-day traffic spikes.
Solution
NestJS 11 backend for 450+ concurrent users: LDAP/Active Directory authentication, JWT authorization, and an OpenAPI-documented REST API with pagination and filtering pushed down to the database.
Stack
Hardware R&D, Shenzhen · Shenzhen R&D
Problem
The A10M printer had structural and motion-control weaknesses that firmware tuning alone could not compensate for.
Solution
Structural redesign of printer components in Fusion 360, combined with Klipper firmware optimization and improved stepper motor control.
Stack
ThingsBoard integration for the heating industry · AWS alerting
Problem
District-heating operators find out about pipe degradation after a failure. The impedance data existed, but never reached anyone who could act on it.
Solution
Impedance monitoring built on ThingsBoard: embedded C++ firmware feeding a web interface, with AWS-based alerting on threshold breaches.
Stack
KonikSystems · KONIK · 03.2026 - 08.2026 · Remote
Randlab Software · Anatomy Project · 09.2025 - 02.2026 · Remote
GEEETECH · 08.2024 - 08.2025 · Remote · Shenzhen R&D team
Randlab Software (Polsat Plus Group) · 04.2023 - 07.2024 · Remote
Randlab Software · 09.2022 - 03.2023 · Nowy Sącz, Poland
Alongside my software and infrastructure work, I take on independent technical consulting projects involving embedded Linux, Armbian, Klipper, Marlin and 3D-printer hardware. 32 public reviews since 2022, 31 of them at five stars, from clients in ten countries. Every review is publicly verifiable on Fiverr.
This guy knows what he is doing. Helped me get my modified ender 3 printing again. I have been scratching my head on the problems with it for months and he helped me get it working in a couple days.
ccrank85 · US
Was very helpful and willing to help immediately. Was also very flexible in helping with the issue we were in vastly different time zones. 10/10 would reach out for consulting again.
skilnotfound · US
I explore evolutionary computation for algorithmic trading: generating strategy populations in StrategyQuant X, then stress-testing their robustness before live execution.
WSB National Louis University · Cracow, Poland · 10.2024 – Present
Technical School of Electrical Engineering and Mechanics · Nowy Sącz, Poland · Completed
Open to backend, platform and system-architecture work — remote or Cracow, Poland.