Senior Full-Stack Engineer (TypeScript, React, Node.js)

About the role
A seed-stage B2B SaaS company is building subscription infrastructure for e-commerce: billing, checkout and developer tools. They need a full-stack engineer who owns features from idea to release. You'll work across frontend and backend, talk to designers and founders directly, and help shape the architecture as the product grows.

What you will do

• Build and ship full-stack features in TypeScript, with React on the frontend and Node.js on the backend.
• Own features end to end: clarify requirements, propose an approach, build, test, release and check the impact.
• Build merchant-facing subscription, billing and checkout flows that are clear and reliable.
• Improve the developer-facing side of the product: APIs, docs, integrations, onboarding and error messages.
• Turn Figma designs into clean, accessible UI and suggest practical UX improvements.
• Keep the architecture simple, observable and maintainable. No over-engineering.
• Do code reviews, write automated tests and keep documentation useful.
• Use AI coding tools where they save time or improve quality.

Requirements

• Fluent Polish and residence in Poland.
• 5+ years of professional software engineering experience, mostly in product or SaaS companies, not only agencies or consulting.
• Strong TypeScript and Node.js in production, with features used by real customers.
• Production experience with React.
• Experience taking at least one customer-facing feature from requirements to release.
• Comfortable working from Figma designs.
• Able to work independently in an early-stage team without detailed specs.

Nice to have

• Next.js, or Vue and Nuxt.
• Fastify, Express or NestJS.
• Payments or subscriptions: recurring billing, payment providers, invoicing, proration, dunning.
• E-commerce: Shopify, WooCommerce, Magento or headless commerce.
• Public APIs, SDKs, webhooks or developer documentation.
• Startup experience, especially in teams under 200 people.
• Hands-on use of AI and LLM tools (Cursor, Copilot, Claude, OpenAI).