Senior Fullstack Engineer

At Upside were partnering with ambitious companies across the globe to solve complex meaningful problems through technology. We work in focused teams combining engineering product thinking and design to deliver outcomes not just output.

Open-source is a strategic part of our work. We build and maintain a number of open-source projects that support our clients and internal R&D. Our latest release is Enthusiast a customizable agentic AI toolkit for e-commerce.

Youll have a Founder mindset. You wont just build a UI or a database - youll own the entire product experience. Youll be a technical partner to stakeholders helping them understand whats possible with modern tech and AI. Youll have the autonomy to experiment across the stack and the responsibility to deliver tools that actually solve business problems.

Youll work at the intersection of product thinking and engineering deploying AI-augmented features across the entire stack.

As a Senior Fullstack Engineer youll design and scale resilient systems from the ground up. Youll bridge the gap between backend logic and frontend experience ensuring a seamless production-grade product.

• End-to-End Ownership: Lead the design and implementation of both backend systems and frontend interfaces.

• Proactive Solutions: Dont just flag blockerscome with proposals and experiments to bypass them.

• Consulting: Translate complex business needs into elegant scalable fullstack architecture.

• Engineering Standards: Advocate for code quality security and performance across the entire repo.

• Continuous Improvement: Constantly evaluate new tech (especially AI/LLM) to improve delivery.

• Experience: 5 years of building complex web applications.

• Backend: Strong proficiency in Python or Ruby.

• Frontend: Mastery of or .

• Infrastructure: Solid understanding of SQL (PostgreSQL) CI/CD and cloud environments.

• AI-Native: You use tools like Claude or Cursor to build better and faster.

• English: Fluent (C1) for direct client collaboration.

Tech Stack: Python Ruby PostgreSQL AWS Docker.

• Built for the long run We hire for the company not just a project - looking for passion driven engineers who want to grow with Upside over time

• Small teams real accountability. 3-9 people per engagement. Were small by design. That means your decisions carry weight and you are visible.

• Mission-critical work: We handle complex projects that move the needle for international brands. Our clients are scaling companies established international brands and large institutions. The systems you build will be under real load with real stakes.

• Real Ownership: You take part in the decision making process on technology and empowered to take initiative experiment and drive solutions that create real impact.

• No Micromanagement: We trust you to own your work and deliver outcomes - no unnecessary oversight.

• Collaborative R&D: Contribute to targeted Open-source projects and internal AI research.

• Growth through challenges: Complex problems and direct client exposure means youll grow by action.

• Applied AI as a first-class discipline. We dont bolt AI onto projects as an afterthought. Youll identify where it genuinely moves the needle and lead the implementation - on client work and on our own open-source tooling.

• The tools you want. If something makes you faster or sharper we want you using it.

• Transparent progression path. We have defined engineering levels with clear criteria - youll know exactly what each role looks like and what it takes to get from one to the other. No ambiguity no waiting for someone above you to move on

If you didnt find all the information you were looking for have a look at our handbook - it covers a variety of different matters that could be important at this stage. If theres anything else we did not mention that youre interested in - share your thoughts with us

Salary:

Senior Engineer: 20 800 - 25 900 PLN net VAT
Lead Engineer: >25 900 PLN net VAT

Location:

Office in Kraków hybrid fully-remote.