← yelon.dev / About
Backend & Platform Engineer · Cracow, Poland
Wiktor Jeleń is a backend and platform engineer based in Cracow, Poland. He builds multi-tenant production systems, infrastructure and security-critical backends, and wrote PythonMetaTrader5, an open-source order-execution library with more than 42,000 downloads on PyPI.
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
Wiktor Jeleń is a backend and platform engineer based in Cracow, Poland. He builds multi-tenant production systems, infrastructure and security-critical backends, and is the author of PythonMetaTrader5, an open-source order-execution library with more than 42,000 downloads on PyPI.
Wiktor Jeleń works across four areas: backend systems (TypeScript, NestJS, Python, FastAPI, PostgreSQL), platform and infrastructure (Linux, Docker, Nginx, GitHub Actions, AWS, CI/CD), system architecture (multi-tenant isolation, workflow orchestration, failure modes, integration testing) and AI integration (multi-provider LLM layers, Model Context Protocol, evaluation harnesses).
Wiktor Jeleń is based in Cracow, Poland, and is an EU citizen. He works remotely with clients in Europe, North America and Asia, and has run hardware R&D directly with a team in Shenzhen, China.
PythonMetaTrader5 is an open-source Python library written by Wiktor Jeleń that wraps the MetaTrader 5 terminal API for algorithmic trading. It normalizes order placement, handles the full set of broker return codes and adds the safeguards the native API leaves out, so a strategy can run against a live account. It has passed 42,000 downloads on PyPI.
Yes. Alongside software and infrastructure work, Wiktor Jeleń takes independent consulting projects in embedded Linux, Armbian, Klipper, Marlin and 3D-printer hardware. That track has 32 public reviews since 2022, 31 of them at five stars, from clients in ten countries, all readable on his public Fiverr profile.
"Jeleń" is the Polish word for deer, and "Yelon" is roughly how it sounds to an English speaker. Wiktor Jeleń uses Yelon as an online handle and as the name of this site, yelon.dev.
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 work system-first. Architecture, invariants and failure modes get decided before implementation, and behaviour is held in place by tests and explicit constraints rather than by convention — because the systems I am usually asked to build are the ones where a quiet failure is expensive: tenant data that must not leak across a boundary, an order that must not be sent twice, an authentication path that a whole faculty depends on during an exam.
The second track is hardware. I spent a year on R&D with a printer manufacturer in Shenzhen and have taken paid embedded Linux and firmware work continuously since 2022. It is not a hobby next to the software work; it is the reason I am comfortable at the layer where the two meet.
Multi-tenant automation platform · Lead developer & architect · 03–08.2026 · Architecture & delivery
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.
Open-source order-execution library · 42,000+ PyPI downloads
A Python layer over MetaTrader 5 built for algorithmic trading: order normalization, full retcode handling and safeguards that keep execution stable against real capital.
Trading automation system · Docker image · CI/CD
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.
Medical University of Silesia platform · 450+ concurrent users
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.
Hardware R&D, Shenzhen · Shenzhen R&D
Structural redesign of printer components in Fusion 360, combined with Klipper firmware optimization and improved stepper motor control.
ThingsBoard integration for the heating industry · AWS alerting
Impedance monitoring built on ThingsBoard: embedded C++ firmware feeding a web interface, with AWS-based alerting on threshold breaches.
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.
I explore evolutionary computation for algorithmic trading: generating strategy populations in StrategyQuant X, then stress-testing their robustness before live execution.
The same person, on the accounts worth checking:
Open to backend, platform and system-architecture work — remote or Cracow, Poland.
root@yelon.dev · +48 576 706 766
Back to yelon.dev — projects, skills and the full review feed.