Java Developer (with Python proficiency)

At xfive, we are looking to expand our backend team with a mid- to senior-level engineer who brings expertise in Java and has a basic+ working knowledge of Python to help us deliver robust systems across a range of projects. In this full-time freelance role, you’ll do more than just code; you’ll communicate directly with clients and help shape the architecture of our solutions.

What We Offer

We’re all about building a team where you can thrive and do your best work. Here’s what you’ll love about working with us:

• Freelance opportunity: Enjoy the flexibility of a freelance contract and earn between 25 and 35 USD per hour, depending on your experience and expertise.

• Room to grow: We support continuous learning and professional development to help you advance your career.

• Make an impact: Your ideas and work will directly influence our direction and help drive meaningful change.

• Diverse projects: Work on exciting projects for startups, agencies, and companies based in the US, UK, and Australia.

• Work your way: Choose to work from home, your favorite coffee shop, or our Kraków office (we’ve got a nice parking space too!).

• Set your schedule: Work the hours that suit you best, as long as there's some overlap with the team and clients.

• Transparency: We’re open and honest about the company’s decisions, direction, and performance, so you’re always in the loop.

• Supportive team: You’ll never be left alone. Our team is collaborative and always ready to help each other.

• Great vibes: Join a team of open-minded, fun, and friendly people who enjoy what they do.

• Stay connected: Participate in social events, both online and in person, to stay engaged and build connections.

Must-Haves:

• At least 6 years of professional software development experience, including:

  • 5+ years with Java Spring Boot

  • 2+ years with Python.

• Strong verbal and written English communication skills (B2+ level), with the ability to talk directly with clients in online meetings.

• Ability to deliver high-quality service and work independently.

• Availability of at least 40 hours per week.

• Solid programming fundamentals and understanding of best practices (e.g., DRY, KISS, abstraction, refactoring, optimization, security).

• Strong understanding of software design patterns for scale and efficient code re-use.

• Strong understanding of Microservices with OpenAPI, gRPC, and Protobufs.

Java:

• Strong command of Java and Spring Boot.

• Familiarity with non-relational databases like MongoDB.

• Experience building RESTful APIs and working with microservices.

• Understanding of Java concurrency and multi-threading.

• Experience with testing frameworks like JUnit and Mockito.

• Familiarity with Spring Security for authentication and authorization.

• Proficiency with build tools such as Maven or Gradle.

• Experience with containerization (Docker) and orchestration platforms (e.g., Kubernetes).

• Good understanding of logging and monitoring tools for Java apps (e.g., SLF4J, Logback, ELK stack).

• Familiarity with JVM performance tuning.

Python: 

• Solid grasp of Python 3.x syntax, idioms, and best practices.

• Strong understanding of object-oriented and functional programming paradigms in Python.

• Familiarity with virtual environments and dependency management tools (venv, pip, Poetry).

• Proficiency in writing unit and integration tests with pytest or unittest.

• Comfortable packaging modules and managing releases (e.g., setuptools, wheel, PyPI).

• Experience with logging, debugging, and performance profiling (cProfile, logging module).

• Basic knowledge of asynchronous programming  with asyncio or async libraries

• Ability to work with databases via ORMs or direct drivers.

• Understanding of API serialization and request validation.

Nice-to-Haves:

• Basic Polish proficiency (A2+level) to communicate with our local team.

• Exposure to task queues and concurrency tools.

• Familiarity with static typing and linting.

• Experience containerizing Python applications.

• Knowledge of CI/CD workflows for Python.

• Hands-on with data-processing libraries (pandas, NumPy).