Available to hire
Hi, I’m Sebastian Mroz. I’m a Senior Full-Stack Engineer with 10+ years crafting scalable, cloud-native web applications using React/Next.js, Node.js/NestJS, and modern AI integrations. I focus on performance, reliability, and developer experience, delivering product value end-to-end from architecture to deployment.
I’m passionate about building robust microservices, infrastructure-as-code, and DevOps automation across AWS, Azure, and GCP. I enjoy mentoring teams, shaping clean code practices, and exploring AI tooling to create data-driven features that truly empower users.
Skills
Experience Level
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Intermediate
Language
Polish
Advanced
English
Fluent
Work Experience
Senior Software Engineer at Sii Poland
September 30, 2025 - October 14, 2025Led design and development of a patient engagement and analytics platform using Next.js, NestJS, and TypeScript, integrating OpenAI APIs and LangChain for intelligent triage and automated care recommendations. Built RAG pipelines with PostgreSQL, Redis, and vector search to support LLM-based document retrieval, reducing query latency by 45% and improving diagnostic accuracy. Architected microservices deployed on AWS ECS + Lambda, using Terraform for IaC and GitHub Actions for CI/CD to achieve 99.98% uptime and fully automated deployments. Implemented AI-powered conversational interfaces and secure RESTful/GraphQL APIs (FHIR, Stripe, Firebase) with GDPR compliance. Introduced Redis caching and query optimization, reducing response times by 30% for critical endpoints. Monitored performance with Grafana and CloudWatch, enforced JWT/OAuth2 security, and mentored 4 developers on NestJS and AI toolchains.
Senior Software Engineer at Sii Poland
September 1, 2025 - October 14, 2025Led design and development of a patient engagement and analytics platform using Next.js, NestJS, and TypeScript; integrated OpenAI APIs and LangChain for intelligent triage and automated care recommendations. Built RAG pipelines with PostgreSQL, Redis caching, and vector search to reduce query latency by 45% and improve diagnostic accuracy. Architected microservices on AWS ECS + Lambda, leveraging Terraform for IaC and GitHub Actions for CI/CD; achieved 99.98% uptime and fully automated deployments. Integrated AI SDKs and prompt-engineering workflows for conversational interfaces powering virtual assistants used by 20K+ patients. Designed secure RESTful and GraphQL APIs for interoperability with third-party systems (FHIR APIs, Stripe, Firebase), ensuring GDPR compliance and high availability. Implemented unit/integration tests with Jest and Cypress, achieving 85% code coverage. Deployed infrastructure with Docker and Kubernetes (EKS), optimizing build pipelines and reducing deployment
Senior Software Engineer at Sii Poland
September 1, 2025 - October 14, 2025Led development of a HIPAA-compliant wellness and patient tracking platform using Next.js (React 18) and Python (FastAPI), deployed on AWS (ECS, Lambda, API Gateway, S3, RDS) and GCP (Cloud Run, Firestore); improved deployment speed by 40%. Designed microservice architecture with Docker, Kubernetes (EKS), and Terraform, achieving 99.95% uptime. Implemented CI/CD workflows with GitHub Actions and Jenkins. Developed GraphQL & RESTful APIs for wearable data ingestion, integrated PostgreSQL & Redis for caching and real-time analytics. Enhanced frontend performance with Next.js App Router, TypeScript, TailwindCSS, Redux, and Storybook. Implemented security practices (JWT auth, Cognito, HTTPS, OWASP Top 10) and role-based access with audit logging. Built unit & integration tests (Pytest, Jest, Cypress) with ~85% coverage. Integrated Stripe, Firebase, and third-party EHR systems; optimized API latency by 25%. Created observability with Prometheus, Grafana, and CloudWatch. Collaborated in Agil
Senior Software Engineer at Sii Poland
September 1, 2025 - October 14, 2025Led development of HIPAA-compliant wellness and patient tracking platform using Next.js (React 18) and Python (FastAPI), deployed on AWS (ECS, Lambda, API Gateway, S3, RDS) and GCP (Cloud Run, Firestore); improved deployment speed by 40%. Integrated AI-assisted health insights using OpenAI APIs, LangChain, and RAG pipelines for personalized recommendations and chat-based coaching. Designed microservice architecture with Docker, Kubernetes (EKS), and Terraform, ensuring scalable and cost-optimized infrastructure; achieved 99.95% uptime. Implemented CI/CD workflows using GitHub Actions + Jenkins, automating testing and deployment across environments, cutting release time by 35%. Developed GraphQL & RESTful APIs for wearable device data ingestion, integrated PostgreSQL & Redis for caching and real-time analytics. Enhanced frontend performance with Next.js App Router, TypeScript, TailwindCSS, Redux, and Storybook, reducing load times by ~30%. Applied security best practices (JWT auth, Cogn
Senior Software Engineer at DataArt
November 30, 2022 - October 14, 2025Developed multi-tenant CRM and analytics SaaS for SMB clients using Next.js, Express.js, and TypeScript; hosted on AWS (EC2, S3, RDS) with automated CI/CD via Jenkins. Designed microservices and REST APIs handling user management, billing, and reporting, integrated with Stripe and Firebase for payments and authentication. Implemented real-time dashboards using React Hooks, Redux, and WebSockets, improving client reporting visibility by 40%. Migrated monolith services to NestJS-based microservices, enhancing scalability and modularity; reduced build time by 35%. Deployed infrastructure-as-code using Terraform, managing environments across staging, dev, and prod on AWS. Led integration of OpenAI-powered analytics assistant, enabling natural-language queries on CRM data via LangChain + Node.js APIs. Used PostgreSQL, MongoDB, and Redis with TypeORM for persistence; optimized queries and indexing to cut response times by 25%. Set up unit/E2E testing frameworks using Jest, Cypress, and Postm
Senior Software Engineer at DataArt
November 30, 2022 - October 14, 2025Developed a multi-tenant CRM and analytics SaaS for SMB clients using Next.js, Express.js, and TypeScript, hosted on AWS (EC2, S3, RDS) with automated CI/CD via Jenkins. Designed microservices and REST APIs for user management, billing, and reporting; integrated Stripe and Firebase for payments and authentication. Implemented real-time dashboards with React Hooks, Redux, and WebSockets, improving client visibility by 40%. Migrated monolith services to NestJS-based microservices, enhancing scalability and reducing build times by 35%. Used Terraform for IaC to manage environments across staging, dev, and prod. Led integration of OpenAI-powered analytics with LangChain and Node.js APIs to enable natural-language queries on CRM data. Worked with PostgreSQL, MongoDB, Redis; TypeORM for persistence, optimizing queries leading to faster response times by 25%. Established unit/e2e testing with Jest, Cypress, and Postman; improved reliability and regression coverage. Optimized front-end perform
Senior Software Engineer at DataArt
November 1, 2022 - October 14, 2025Contributed to credit risk and fraud detection system using Python (Django, FastAPI) and React, AWS Lambda + RDS; supported >1 million daily transactions. Designed microservice architecture with REST + GraphQL APIs, integrating Kafka & RabbitMQ for real-time data pipelines. Applied ML models for fraud scoring and risk classification, reducing false positives by 22%. Built admin and analytics dashboards in React + Redux + Material UI with D3.js visualizations. Automated provisioning using Terraform and AWS CDK; CI/CD with Jenkins and GitHub Actions. Implemented secure auth with AWS Cognito and OAuth2, ensuring PCI DSS compliance. Performance optimizations and comprehensive testing (Pytest, Jest, Postman). Collaborated with business analysts in Agile Scrum.
Senior Software Engineer at DataArt
November 1, 2022 - October 14, 2025Contributed to credit risk and fraud detection system using Python (Django, FastAPI), React, and AWS Lambda + RDS, supporting more than one million daily transactions. Designed microservice architecture with REST + GraphQL APIs, integrating with Kafka & RabbitMQ for real-time data pipelines. Applied machine learning models for fraud scoring and risk classification using Pandas, NumPy, and scikit-learn, reducing false positives by 22%. Developed admin and analytics dashboards in React +Redux +Material UI, integrating with D3.js for financial visualizations. Automated provisioning using Terraform and AWS CDK, achieving repeatable infrastructure and reducing manual setup by 70%. Set up CI/CD pipelines with Jenkins and GitHub Actions, automating builds, tests, and deployments across dev and prod. Implemented secure auth flows with AWS Cognito and OAuth2, ensuring PCI DSS compliance. Conducted performance optimization (query tuning, caching with Redis, async workers) resulting in 30% faster
Software Engineer at Innovecs
July 31, 2019 - October 14, 2025Developed scalable marketplace platform using React, Redux, Node.js, and Express, supporting 100K+ monthly active users. Built payment integrations with Stripe and PayPal APIs, ensuring PCI-DSS compliance and secure transactions. Designed and optimized RESTful APIs with PostgreSQL and Redis, achieving 40% faster page loads via efficient caching. Implemented microfrontend architecture and component reuse with Storybook and TailwindCSS, reducing UI duplication by 30%. Wrote integration and unit tests using Mocha and Chai, improving QA stability. Deployed applications on AWS EC2 with Docker, integrated Jenkins CI/CD pipelines, and automated build/test workflows. Collaborated closely with product teams to improve checkout flow, increasing conversion rates by 12%. Participated in code reviews and Agile ceremonies to ensure code quality and delivery predictability.
Software Engineer at Innovecs
July 31, 2019 - October 14, 2025Developed a scalable marketplace platform using React, Redux, Node.js, and Express, supporting 100K+ monthly active users. Implemented payment integrations with Stripe and PayPal ensuring PCI-DSS compliance. Designed RESTful APIs with PostgreSQL and Redis, achieving faster page loads through caching. Implemented microfrontend architecture with Storybook and TailwindCSS, reducing UI duplication. Wrote integration and unit tests with Mocha and Chai; deployed on AWS EC2 with Docker and Jenkins-based CI/CD; improved checkout flow and conversion. Collaborated with product teams to refine features and improve performance; participated in code reviews and Agile ceremonies.
Software Engineer at Innovecs
July 1, 2019 - October 14, 2025Developed research data management platforms using Python (Flask, Pandas, NumPy) and React, enabling interactive data visualization. Implemented ETL pipelines for AWS S3 + Lambda + Athena and GCP BigQuery, reducing data latency by 50%. Containerized services with Docker and deployed to Kubernetes (GKE) for scalability. Integrated MongoDB and PostgreSQL via SQLAlchemy and Prisma, ensuring data versioning and audit trails. Built data visualization dashboards with React + D3.js and improved reliability through unit testing and code reviews.
Software Engineer at Innovecs
July 1, 2019 - October 14, 2025Developed research data management platforms using Python (Flask, Pandas, NumPy) and React, enabling interactive data visualization. Implemented ETL pipelines for processing scientific datasets on AWS S3 + Lambda + Athena and GCP BigQuery, reducing data latency by 50%. Containerized services with Docker and deployed to Kubernetes (GKE) for scalability and cost efficiency. Integrated MongoDB and PostgreSQL via SQLAlchemy and Prisma, handling data versioning and audit trails. Built data visualization dashboards using React + D3.js, helping non-technical users interpret analytical outputs. Ensured reliability through unit testing (Pytest, Mocha) and code reviews under Agile sprints. Improved system security with JWT auth and HTTPS enforcement across services. Worked closely with scientists and engineers to automate repetitive data tasks, reducing manual effort by 60%.
Junior Software Engineer at Atos Poland
March 31, 2016 - October 14, 2025Supported development of internal enterprise dashboards using AngularJS, JavaScript, and C#/.NET APIs. Implemented RESTful endpoints and SQL stored procedures to retrieve business metrics from MySQL and PostgreSQL. Assisted with unit testing and bug triage using JIRA and Postman, improving issue resolution speed. Collaborated with senior engineers to refactor legacy codebases following SOLID principles and TDD. Participated in Agile/Scrum sprints, learning CI with Jenkins and Git workflows.
Junior Software Engineer at Atos Poland
March 31, 2016 - October 14, 2025Supported development of internal enterprise dashboards using AngularJS, JavaScript, and C#/.NET APIs. Implemented RESTful endpoints and SQL stored procedures to retrieve business metrics from MySQL and PostgreSQL. Assisted with unit testing and bug triage using JIRA and Postman, improving issue resolution speed. Refactored legacy codebases following SOLID principles and TDD; participated in Agile/Scrum sprints; gained experience with Jenkins and Git workflows.
Junior Software Engineer at Atos Poland
March 1, 2016 - October 14, 2025Assisted in building enterprise web applications using Python (Django) and JavaScript (AngularJS, Bootstrap). Created REST APIs for internal reporting tools with MySQL and Django ORM. Implemented unit tests (Pytest) and participated in code reviews to ensure best practices. Supported deployment to AWS EC2 and S3, configuring CI pipelines for staging environments. Contributed to documentation and Agile stand-ups to improve team delivery speed.
Junior Software Engineer at Atos Poland
March 1, 2016 - October 14, 2025Assisted in building enterprise web applications using Python (Django) and JavaScript (AngularJS, Bootstrap). Created REST APIs for internal reporting tools with MySQL and Django ORM. Implemented unit tests (Pytest) and participated in code reviews to ensure best practices. Supported deployment to AWS EC2 and S3, configuring CI pipelines for staging environments. Contributed to documentation and Agile stand-ups, enhancing team communication and delivery speed.
Education
Engineer’s Degree in Computer Science at Lodz University of Technology
January 1, 2011 - January 1, 2015Master’s Degree in Computer Science at Lodz University of Technology
January 1, 2015 - January 1, 2016Master's Degree in Computer Science at Lodz University of Technology
January 1, 2015 - December 31, 2016Engineer’s Degree in Computer Science at Lodz University of Technology
January 1, 2011 - December 31, 2015Master’s Degree in Computer Science at Lodz University of Technology
January 1, 2015 - January 1, 2016Engineer’s Degree in Computer Science at Lodz University of Technology
January 1, 2011 - January 1, 2015Engineer’s Degree in Computer Science at Lodz University of Technology
January 1, 2011 - December 31, 2015Master’s Degree in Computer Science at Lodz University of Technology
January 1, 2015 - December 31, 2016Qualifications
Industry Experience
Healthcare, Financial Services, Life Sciences, Software & Internet, Professional Services, Media & Entertainment
Skills
Experience Level
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Intermediate
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