Marcel Olszewski

Senior Ruby Software Engineer

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Rzeszów, Poland

Experience

Sep 2020 - Present
5 years 5 months
United States

Senior Ruby Software Engineer

Glorium Technologies

  • Architected Ruby-based service layers using advanced object-oriented patterns and metaprogramming techniques, improving extensibility while reducing long-term maintenance effort by 28%.
  • Reviewed and annotated complex Ruby codebases to identify anti-patterns, code smells, and performance bottlenecks, contributing to a 35% reduction in production defects.
  • Generated high-quality Ruby code samples and edge-case scenarios to support internal AI-assisted tooling and automated reasoning workflows.
  • Evaluated LLM-generated Ruby outputs for correctness, idiomatic usage, and architectural soundness across more than 1,200 annotated examples.
  • Benchmarked Ruby execution paths in sandboxed environments, identifying memory leaks and execution anomalies under constrained runtime conditions.
  • Designed robust RSpec and Minitest suites to close critical test gaps, increasing average code coverage from 72% to 91%.
  • Integrated Ruby test pipelines into CI/CD workflows using GitHub Actions and GitLab CI, reducing regression escape rates by 40%.
  • Debugged concurrency, memory, and I/O-related issues using profiling tools, stack trace analysis, and targeted instrumentation.
  • Documented defects, technical debt, and architectural trade-offs with structured, reproducible steps to support long-term knowledge retention.
  • Collaborated with solution engineers and technical leads to refine experimental guidelines for AI-driven code evaluation workflows.
  • Adapted quickly between unrelated domains and problem statements, maintaining accuracy and output quality under rapidly changing constraints.
  • Validated Ruby code security and reliability by simulating malicious inputs and unexpected runtime conditions in isolated environments.
  • Maintained Dockerized Ruby environments to ensure consistent execution across local, CI, and sandboxed systems.
  • Mentored engineers on idiomatic Ruby practices and effective code review strategies, improving review throughput by 22%.
  • Supported cross-language evaluations by analyzing Python, JavaScript, TypeScript, SQL, and Rust snippets within mixed-language pipelines.
  • Authored detailed internal documentation covering test strategies, annotation guidelines, and AI-assisted development best practices.
Feb 2017 - Aug 2020
3 years 7 months
Poland

Full Stack Developer

SELLEO EdTech

  • Developed Ruby-driven backend systems emphasizing clean architecture, modularity, and long-term maintainability across multiple client projects.
  • Conducted systematic code reviews to uncover logic flaws, test omissions, and structural anti-patterns in evolving Ruby codebases.
  • Implemented comprehensive automated testing strategies, reducing post-release defects by 31% within the first year.
  • Integrated CI pipelines using Jenkins and GitLab CI to enforce quality gates and consistent test execution.
  • Analyzed Ruby performance metrics to eliminate inefficient database queries and redundant object allocations.
  • Refactored legacy Ruby modules to align with idiomatic conventions, improving onboarding speed for new developers by 25%.
  • Collaborated with distributed teams to translate ambiguous requirements into precise, testable technical implementations.
  • Documented technical decisions, bug root causes, and testing approaches to support knowledge sharing across teams.
  • Validated correctness of dynamically generated Ruby code paths under edge-case scenarios and malformed inputs.
  • Supported early experimentation with AI-assisted coding tools by evaluating generated Ruby snippets for reliability and clarity.
  • Maintained Docker-based local environments to standardize development and testing workflows across projects.
Mar 2016 - Feb 2017
1 year
Poland

Full Stack Developer

Boldare

  • Delivered Ruby-based application features using disciplined object-oriented design and consistent coding standards.
  • Reviewed peer code to detect hidden defects, architectural inconsistencies, and insufficient test coverage early in development cycles.
  • Built automated test suites that validated both functional correctness and regression stability across frequent releases.
  • Improved debugging efficiency by introducing structured logging and reproducible defect reports.
  • Refined Ruby modules to reduce cyclomatic complexity and improve readability without altering external behavior.
  • Collaborated closely with consultants and clients to clarify technical constraints and ensure reliable delivery outcomes.
  • Implemented Git-based workflows supporting feature branching, peer reviews, and controlled release processes.
  • Diagnosed environment-specific failures using Linux CLI tools and runtime inspection techniques.
  • Assisted with technical documentation covering application behavior, test scenarios, and known limitations.
  • Adapted quickly to new domains and project requirements while maintaining code quality and delivery timelines.

Summary

Senior software engineer with over 10 years of experience delivering high-quality, production-grade systems across consulting and AI-adjacent environments. Deep expertise in Ruby, object-oriented design, metaprogramming, and code quality evaluation, combined with hands-on experience in LLM-assisted development, code generation, and multi-language analysis. Proven ability to review, annotate, benchmark, and improve complex codebases while collaborating with distributed, research-oriented teams.

Skills

  • Ruby (Oop, Metaprogramming, Idiomatic Ruby, Performance Proiling)
  • Code Review & Static Analysis
  • Llm Training, Prompt Evaluation & Data Annotation
  • Ai-assisted Code Generation & Validation
  • Rspec, Minitest, Test Coverage & Test Gap Analysis
  • Ci/cd (Github Actions, Gitlab Ci, Jenkins, Circleci)
  • Docker & Containerized Ruby Environments
  • Git Version Control & Linux Cli
  • Python, Javascript, Typescript, Sql, Rust (Cross-language Evaluation)
  • Benchmarking & Sandboxed Code Execution
  • Debugging, Defect Documentation & Technical Debt Management
  • High-quality Technical & Test Documentation

Languages

Polish
Native
English
Advanced

Education

Feb 2011 - Nov 2015

The University of Queensland

Bachelor of Computer Science · Computer Science · Australia

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