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

WhyHireWrong? • Łódź, Europe

4d • $100,000 - $120,000

About The Position

A seed-stage B2B SaaS company is building subscription infrastructure for e-commerce, including billing, checkout, and developer tools. The company is seeking a full-stack engineer to own features from idea through release. The role works across frontend and backend, collaborates directly with designers and founders, and helps shape the product architecture as the product grows.

Requirements

• Fluent Polish and residence in Poland.
• At least 5 years of professional software engineering experience, mostly in product or SaaS companies rather than only agencies or consulting.
• Strong production experience with TypeScript and Node.js, including features used by real customers.
• Production experience with React.
• Experience taking at least one customer-facing feature from requirements to release.
• Comfort working from Figma designs.
• Ability to work independently in an early-stage team without detailed specifications.

Nice To Haves

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

Responsibilities

• Build and ship full-stack features using TypeScript, React, and Node.js.
• Own features end to end: clarify requirements, propose an approach, build, test, release, and assess impact.
• Build clear and reliable merchant-facing subscription, billing, and checkout flows.
• Improve developer-facing APIs, documentation, integrations, onboarding, and error messages.
• Turn Figma designs into clean, accessible UI and suggest practical UX improvements.
• Keep architecture simple, observable, and maintainable, avoiding over-engineering.
• Conduct code reviews, write automated tests, and maintain useful documentation.
• Use AI coding tools where they save time or improve quality.

What This Job Offers

• Job Type: Full-time
• Career Level: Senior
• Education Level: No Education Listed