O Oskar Karpiński

Skills & Expertise

Languages, frameworks, and tools I use to design, build, and deploy production-grade software - backend APIs, mobile clients, websites, infrastructure, and CI/CD pipelines.

Backend Development

Designing and implementing scalable server-side systems - from RESTful APIs to microservices.

Java/Kotlin

Developing backend services with Spring Boot and Ktor.

  • Spring Boot
  • Spring Data JPA
  • Spring Security
  • Hibernate
  • Ktor
  • Coroutines

Go

Building efficient backend services and microservices with Gin and Fiber.

  • Gin
  • Fiber
  • GORM
  • Goroutines
  • Channels
  • Context

C#

Building web applications and APIs with ASP.NET Core and Entity Framework Core.

  • .NET
  • ASP.NET
  • Entity Framework Core

API Design

Designing and documenting RESTful, GraphQL, and gRPC APIs.

  • RESTful API
  • GraphQL
  • gRPC
  • JWT
  • OpenAPI

Mobile Development

Building native mobile apps using Jetpack Compose and cross-platform frameworks like Flutter and React Native with high performance and scalability in mind.

Jetpack Compose

Building native Android apps with Jetpack Compose and Kotlin Multiplatform.

  • KMP
  • Compose Multiplatform
  • State Management
  • Navigation
  • View Models
  • Dagger Hilt

Flutter

Cross-platform apps with Flutter.

  • Flutter
  • Dart
  • Isolates
  • Material Design

React Native

Cross-platform apps with React Native and Expo.

  • Expo
  • Expo Router
  • NativeWind

Web Development

Developing websites using modern frameworks like React, Next.js, and Astro.

React

Building interactive UIs with React.

  • JSX
  • Functional Components
  • Hooks
  • Redux
  • React Query
  • Context API
  • React Router

Next.js

Developing SSR and static websites with Next.js.

  • SSR
  • SSG
  • ISR
  • API Routes
  • App Router
  • Pages Router
  • Data Fetching
  • Vercel

Astro

Building fast content-focused websites with Astro.

  • Islands Architecture
  • MPA
  • Partial Hydration
  • MDX
  • SSG

Gatsby

Building static sites with Gatsby's GraphQL data layer.

  • GraphQL
  • SSG
  • Plugins
  • Themes

Svelte/SvelteKit

Building reactive web apps with Svelte and SvelteKit.

  • Reactive Programming
  • Stores
  • Actions
  • Server-side Rendering

Styling & UI Frameworks

Modern CSS frameworks for responsive and aesthetic designs.

  • Tailwind CSS
  • Styled-components
  • Sass/SCSS/PostCSS
  • Material UI

Infrastructure & DevOps

Infrastructure management and DevOps with Docker, Linux, and CI/CD.

Docker

Containerizing applications for consistent environments.

  • Docker Engine
  • Docker Compose
  • Containerization
  • Image Building

Linux Administration

Managing Linux servers for production environments.

  • Bash
  • Shell Scripting
  • Ubuntu
  • Debian
  • CentOS
  • Systemd
  • Networking
  • Permissions

CI/CD & Automation

Setting up CI/CD pipelines for automated testing and deployment.

  • GitHub Actions
  • GitLab CI/CD
  • Automation
  • Pipelines

Databases

Designing and managing relational and NoSQL databases.

  • MySQL
  • MariaDB
  • PostgreSQL
  • Redis
  • MongoDB
  • SQL
  • NoSQL
  • Database Design
  • Optimization

Object-Relational Mapping (ORM)

Using ORMs for object-oriented database interaction.

  • Hibernate
  • Spring Data JPA
  • GORM
  • Entity Framework Core
  • Prisma
  • TypeORM

Big Data & Analytics

Data engineering, analysis, and AI-driven insights.

Python for Data Analysis

Data analysis with Pandas, NumPy, and statistical tools.

  • Python
  • Pandas
  • NumPy
  • Data Analysis

SQL

Advanced SQL for complex queries and data aggregation.

Data Collection & Web Scraping

Web scraping and API integration for data acquisition.

  • Web Scraping
  • API Integration

AI Agents

Analyzing data with AI agents and ML models.

  • AI Agents
  • OpenAI APIs

Development Workflow & Tools

Testing, version control, IDEs, and AI-assisted development.

Testing

Unit, integration, and E2E testing across platforms.

  • Unit Testing
  • Integration Testing
  • End-to-End Testing
  • JUnit
  • Go Test
  • Jest
  • Vitest

Version Control

Managing source code with Git on GitHub and GitLab.

  • Git
  • GitHub
  • GitLab
  • Branching Strategies
  • Code Reviews

IDEs & Tools

IntelliJ IDEA, Android Studio, VS Code, and terminal tools.

  • IntelliJ IDEA
  • Android Studio
  • VS Code
  • Terminal
  • Postman
  • Insomnia

AI Pair Programming

AI-assisted development with Copilot, Claude, and OpenCode.

  • GitHub Copilot
  • Claude Code
  • OpenCode
  • AI Assisted Development

Interested in working together?

I'm available for freelance projects - from websites and mobile apps to backend systems and APIs. Let's connect and see how I can help bring your ideas to life.