Senior Full-Stack Engineer (m/f/d)

Buying Labs

13h•Onsite

About The Position

Buying Labs is seeking a Senior Full-Stack Engineer to join its Tech team at the Hamburg headquarters. The role focuses on building systems that support the business, including internal applications and the data and AI capabilities behind them. The engineer will own work from design through production deployment and support, and work directly with commercial and operational teams to understand business processes and shape solutions. The position spans frontend and backend development, AI feature design and integration, PostgreSQL data modelling, and architecture decisions. The engineer will build new applications on the modern stack while maintaining and modernising an established JavaScript platform. They are expected to deliver reliable, tested and reviewed code, monitor production systems, troubleshoot issues, and share knowledge.

Requirements

At least 6 years of professional software engineering experience, including a track record of building and running production applications end to end.
Proven experience building AI into production systems or applications, such as LLM-based extraction or classification, RAG, or agentic and tool-use workflows.
Ability to make AI outputs reliable through validation, evaluation, and fallbacks; using AI coding assistants alone does not meet this requirement.
Daily use of AI tools in development and strong habits for checking and reviewing their output.
Strong TypeScript and JavaScript skills and experience with modern React, including hooks and state management.
Strong backend experience with Node.js and Express or a comparable framework, REST APIs, and external system integrations.
Deep PostgreSQL and SQL skills, solid data modelling experience, and experience with an ORM or query builder such as Knex, Sequelize, or Prisma.
Comfort working with both modern TypeScript applications and an established JavaScript codebase.
Strong quality mindset, including automated testing, code reviews, and responsibility for shipped work.
High ownership and initiative, including driving work to completion, raising problems early, and independently identifying next steps.
Clear communication with technical and non-technical colleagues.
Bachelor's degree in Computer Science or a related field, or equivalent experience.
Fluent English.
Based in Hamburg or willing to relocate.

Nice To Haves

German language skills.
Experience with LLM provider APIs such as Anthropic, OpenAI, or Gemini; agent and tool-use patterns such as MCP; and evaluating output quality.
Experience with vector search such as pgvector or similar.
Product or process awareness, including understanding business operations and turning complex processes into structured systems.
Experience integrating ERPs or operational systems involving orders, inventory, or master data.
Experience with the wider stack: Bun, Vite, Redis, RabbitMQ, Docker, GitHub Actions, or AWS.
Experience with observability and product analytics tools such as Sentry, Datadog, or PostHog.
Python experience for data tooling.
Background in eCommerce, wholesale, or B2B environments.

Responsibilities

Design, build, deploy, and support features across frontend and backend, owning systems end to end.
Design and integrate AI-powered features such as structured extraction, classification, automation, and agentic workflows.
Improve AI reliability through validation, evaluation, and human review where appropriate.
Build PostgreSQL data models that support applications and AI features, and make architecture decisions that keep systems maintainable as they grow.
Build new applications on the modern stack and maintain and modernise the established JavaScript platform.
Write tested and reviewed code, verify work before release, and monitor and troubleshoot production issues.
Work directly with commercial and operational teams to understand processes and help determine what gets built and why.
Share knowledge and contribute to raising engineering standards.

Benefits

Collaborative, ambitious, and friendly team environment.
Flat hierarchies, role ownership, and personal growth opportunities, including promotion from within.
Modern office setup with adjustable desks, mobile treadmills, and air conditioning.
Company pension program with a 30% Buying Labs contribution grant.
Corporate Benefits membership with discounts from partner brands and retailers.
Full coverage of the Deutschlandticket.
Choice of a complimentary Swapfiets bike or JobRad bike leasing with an additional €26 per month grant.
Free Friday lunch, organic fruit and vegetables, drinks, snacks, coffee and tea, healthy shots, and seasonal treats.
€100 welcome voucher for personalising the workspace.
Employee referral program with rewards.