Marcel Olszewski - Senior Ruby Software Engineer

Q: Where is Marcel based?

Marcel is based in Rzeszów, Poland .

Q: What languages does Marcel speak?

Marcel speaks the following languages: Polish (Native), English (Advanced) .

Q: How many years of experience does Marcel have?

Marcel has at least 10 years of experience. During this time, Marcel has worked in at least 2 different roles and for 3 different companies . The average length of individual experience is 3 years and 4 months . Note that Marcel may not have shared all experience and actually has more experience.

Q: What is Marcel's latest experience?

Marcel's most recent position is Senior Ruby Software Engineer at Glorium Technologies .

Q: What companies has Marcel worked for in recent years?

In recent years, Marcel has worked for Glorium Technologies .

Q: Which industries is Marcel most experienced in?

Marcel is most experienced in industries like Information Technology (IT) and Education .

Q: Which business areas is Marcel most experienced in?

Marcel is most experienced in business areas like Information Technology (IT) , Quality Assurance (QA) , and Product Development .

Q: Which industries has Marcel worked in recently?

Marcel has recently worked in industries like Information Technology (IT) .

Q: Which business areas has Marcel worked in recently?

Marcel has recently worked in business areas like Information Technology (IT) and Quality Assurance (QA) .

Recommended expert

Rzeszów, Poland

Experience

Sep 2020 - Present

5 years 6 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.

Industries Experience

See where this freelancer has spent most of their professional time. Longer bars indicate deeper hands-on experience, while shorter ones reflect targeted or project-based work.

Experienced in Information Technology (6.5 years) and Education (3.5 years).

Information Technology

Education

Business Areas Experience

The graph below provides a cumulative view of the freelancer's experience across multiple business areas, calculated from completed and active engagements. It highlights the areas where the freelancer has most frequently contributed to planning, execution, and delivery of business outcomes.

Experienced in Information Technology (10 years), Quality Assurance (10 years), and Product Development (4.5 years).

Information Technology

Quality Assurance

Product Development

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

Profile

Created

January 2026

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Frequently asked questions

Do you have questions? Here you can find further information.

Where is Marcel based?

Marcel is based in Rzeszów, Poland.

What languages does Marcel speak?

Marcel speaks the following languages: Polish (Native), English (Advanced).

How many years of experience does Marcel have?

Marcel has at least 10 years of experience. During this time, Marcel has worked in at least 2 different roles and for 3 different companies. The average length of individual experience is 3 years and 4 months. Note that Marcel may not have shared all experience and actually has more experience.

What roles would Marcel be best suited for?

Based on recent experience, Marcel would be well-suited for roles such as: Senior Ruby Software Engineer, Full Stack Developer.

What is Marcel's latest experience?

Marcel's most recent position is Senior Ruby Software Engineer at Glorium Technologies.

What companies has Marcel worked for in recent years?

In recent years, Marcel has worked for Glorium Technologies.

Which industries is Marcel most experienced in?

Marcel is most experienced in industries like Information Technology (IT) and Education.

Which business areas is Marcel most experienced in?

Marcel is most experienced in business areas like Information Technology (IT), Quality Assurance (QA), and Product Development.

Which industries has Marcel worked in recently?

Marcel has recently worked in industries like Information Technology (IT).

Which business areas has Marcel worked in recently?

Marcel has recently worked in business areas like Information Technology (IT) and Quality Assurance (QA).

What is Marcel's education?

Marcel holds a Bachelor in Computer Science from The University of Queensland.

What is the availability of Marcel?

Marcel is immediately available full-time for suitable projects.

What is the rate of Marcel?

Marcel's rate depends on the specific project requirements. Please use the Meet button on the profile to schedule a meeting and discuss the details.