Senior Software Engineer

🏢 Summary: Senior Fullstack Engineer role with end-to-end ownership of scalable web products, from backend architecture to frontend experiences. The position combines product consulting, AI-augmented development, and technical leadership in small teams, with hybrid or remote work options. 🗂️ Requirements: 5+ years building complex web applications, Proficiency in Python or Ruby, Mastery of Vue.js or React.js, SQL and PostgreSQL knowledge, CI/CD and cloud environment knowledge, Experience using Claude or Cursor, Fluent English (C1) 📃 Skills: Python, Ruby, Vue.js, React.js, SQL, PostgreSQL, CI/CD, AWS, Docker, Claude, Cursor, LLM 🏢 Description: At Upside , we’re 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. What it means for you You’ll have a "Founder" mindset. You won’t just build a UI or a database - you’ll own the entire product experience. You’ll be a technical partner to stakeholders, helping them understand what’s possible with modern tech and AI. You’ll have the autonomy to experiment across the stack and the responsibility to deliver tools that actually solve business problems. You’ll work at the intersection of product thinking and engineering, deploying AI-augmented features across the entire stack. Role Overview As a Senior Fullstack Engineer, you’ll design and scale resilient systems from the ground up. You’ll bridge the gap between backend logic and frontend experience, ensuring a seamless, production-grade product. Responsibilities End-to-End Ownership: Lead the design and implementation of both backend systems and frontend interfaces. Proactive Solutions: Don't just flag blockers—come 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. Requirements Experience: 5+ years of building complex web applications. Backend: Strong proficiency in Python or Ruby. Frontend: Mastery of Vue.js or React.js . 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, Vue.js , React.js , PostgreSQL, AWS, Docker. Value Proposition 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. We're 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 implementation..You’re 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 you’ll grow by action. Applied AI as a first-class discipline. We don't bolt AI onto projects as an afterthought. You'll 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 - you'll 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 didn't 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 there's anything else we did not mention that you're interested in - share your thoughts with us careers@upsidelab.io Compensation & Location Salary: Senior Engineer: 20 800 - 25 900 PLN net + VAT Lead Engineer: >25 900 PLN net + VAT Location: Office in Kraków, hybrid, fully-remote.

🏢 Summary: Fullstack Engineer role building and evolving a subscription-platform product, with broad ownership across backend, frontend, infrastructure, performance, and customer-driven improvements. The offer provides full remote work, competitive pay with ESOP, and the opportunity to shape product and technical decisions in a lean team. 🗂️ Requirements: 5+ years of software engineering experience, Proficiency with AI-assisted development tools, Command-line / terminal fluency, Knowledge of modern web technologies and standards, Experience with the core stack or equivalent technologies, Ability to learn new tools and frameworks quickly, Cross-functional technical collaboration, Fluent Polish, Fluent English at C1 level 📃 Skills: TypeScript, Fastify, PostgreSQL, BullMQ, Redis, JSON, TypeBox, OpenAPI, Vue, Storybook, Kubernetes, Helmfile, GitHub, Segment, Prometheus, Sentry, Slack, Linear, Notion 🏢 Description: About us At Juo, we're building software for businesses that want to build (or upgrade) and run their subscription offering. Business model-wise, Juo is a B2B SaaS company. Our initial and current focus has been on direct-to-consumer ecommerce businesses selling physical products, but our goal is to make Juo components applicable in any industry where a subscription model can be applied for selling things. Juo operates at the intersection of a few areas, like ecommerce and payments, and especially the new platform, with a strong focus on developer experience. The team is lean and consists only of very experienced people. We had built other successful businesses together. We’d built unsuccessful some too and learned a ton from that. We're backed by fantastic investors (MOC, Peak, Kogito, SMOK) and advisors, including domain experts from companies such as PayU, Piwik PRO, and Your KAYA. We've raised our seed round in November. In other words, we have all the resources needed to be able to focus on building the product, shipping fast, and delivering value to the clients. The role: Fullstack engineer Why this role We're looking for an ambitious and mature individual who will help us build Juo — by being a co-creator, not only an executor. We don't put ourselves into any box or "stack". Instead, each of us participates in the product development as broadly as possible, using the stack that works best for the given objective. This role will: Play a major part in the development of the product (not only by delivering its new features) Have a lot of freedom and ownership in day-to-day tasks Help you broaden your current superpowers with new exciting ones Be part of an exciting growth phase in Juo’s journey About the candidates This role is perfect for an individual who wants to have a real impact on a product they're working on. We're looking for an obsessive builder and a curious problem-solver, who knows how to ask the right questions and where to find answers for them. We work with many technologies that work for us best, so you should be open to getting to know new ones if such a need arises. The team's structure is flat, and thus we always seek people who think long-term and are looking for a longer commitment. We want to work only with those who are not driven by opportunism. We take both product development and relationship building equally seriously. Business-wise, we have passed the most difficult stage for any startup — finding the so-called product-market fit, which means we can focus on building and perfecting the product without financial concerns about the purpose of these actions. We are confident in ourselves, in what we do, and in the value we create for ourselves, our clients, and end users. Responsibilities: Building a new major iteration of the product with high extensibility and great developer experience in mind Developing new features and iteratively improving existing ones Finding, investigating, and fixing bugs and performance issues Supporting customers when the above occurs (customer-driven development) Discussing ideas, solutions and technologies with the team Proactively coming up with ideas for development and product improvements Requirements and qualifications: 5+ years of software engineering experience , ideally in a product-focused environment. Strong proficiency with AI-assisted development tools Solid command line / terminal fluency Broad understanding of modern web technologies , standards, and their nuances. Hands-on experience with our core tech stack (listed below) or equivalent technologies. Comfort operating in a fast-paced, lean startup environment. Growth mindset with a proven ability to pick up new tools and frameworks quickly. Strong cross-functional collaboration skills , comfortable discussing technical topics with product, support, and growth teams. Fluent Polish (written and spoken). Fluent English (C1 level), particularly for reading, writing technical documentation, and clear communication. Tech Backend: Modular Fastify server in TypeScript State persitance in Managed Postgresql database Critical and periodic tasks processed in dedicated BullMQ workers with Redis storage Strong I/O validation with JSON schemas generated with TypeBox with automatic OpenAPI schema generation Frontend: Multiple Vue front-ends in TypeScript Context/Provider pattern for state propagation Shared UI components with Storybook integration Automatically generated SDKs shared between front-ends Infrastructure and tools: Managed Kubernetes provisioned with Helmfile Full CI/CD on GitHub actions Data streamed through Segment Observability via Prometheus and Sentry Communication over Slack, Linear and Notion What we offer Building an extraordinary team is a fantastic challenge. We require a lot, but we give back to our teammates as much since they're not company assets, they're founders. What you'll get: Being a part of the team you can trust and rely on Taking an active part in building a revolutionary product loved by its users Competitive salary + Employee Stock Ownership Plan (ESOP) Full time Full remote Team retreats Macbook Pro and all the necessary tools (Slack, GitHub, Linear, Sentry) 1-on-1 access to the founders, investors, and advisors How to apply If this feels like the right fit, email us at jobs@juo.com with your resume, a few words about yourself, and why you want to join us. That's the best way to apply 🙂 You can use the button at the bottom of the page, but if you want to increase your chances, email is the way to go. We don't like long drawn-out processes — so usually the whole thing takes around 2 weeks from start to finish. And we answer every application. If your first email clicks, the next step will be a 15–30 min call with one of us (most of the time one of the founders) and we'll take it from there. Also, share this page if you know someone who might be interested. Either way, we're excited to hear from you! Thank you for your time.