As part of AI-LAB as a Full-Stack Developer, you will be instrumental in building and scaling our AI products. You will own features end-to-end across a modern Next.js frontend and our NestJS backend services, delivering a seamless and powerful user experience. You'll be joining a team with a ship-fast mindset and a modern, carefully curated tech stack. Develop and maintain features on our Next.js (App Router) frontend using TypeScript, SWR, Tailwind, and a component-driven design system, with full internationalization (i18n) support. Design, implement, and maintain RESTful APIs with NestJS (TypeScript) to manage authentication, data processing, billing, usage tracking, and orchestration of AI workflows. Own backend services end-to-end: from schema design and migrations to deployment and observability, and contribute to new services as the product surface grows. Integrate and maintain third-party SDKs and APIs that power critical product flows, including payment processing, authentication, analytics, and messaging. Build AI agents and tools using the Claude SDK and Model Context Protocol (MCP) : giving LLMs real-time access to data, APIs, and tools so they can take meaningful actions on behalf of users. Contribute to schema design with Prisma and PostgreSQL , write and review migrations, and reason carefully about data models that evolve safely over time. Implement and maintain feature flags , A/B experiments, and analytics events so product decisions are driven by data. Handle incoming webhooks and asynchronous task processing with the rigor required for payment-critical and PII-handling code paths (idempotency, retries, fault tolerance). Collaborate with AI product managers and AI specialists to translate complex requirements into robust, scalable features — and push back on complexity when a simpler path exists. Collaborate on application deployment and help maintain our cloud infrastructure. Requirements We are seeking a proactive and skilled developer who is passionate about building modern, AI-driven applications and who treats production code with the care it deserves. TypeScript Proficiency: Highly proficient in TypeScript across both frontend (React/Next.js) and backend (Node.js/NestJS) environments. Frontend Expertise: Strong experience with React and Next.js (App Router) : Server Components, route handlers, streaming, metadata, i18n, and modern data-fetching patterns (SWR or equivalent). Backend Expertise: Solid experience building production REST APIs with NestJS (or comparable Node frameworks like Express/Fastify): modules, DI, guards, interceptors, DTO validation. Database Skills: Experience with PostgreSQL and an ORM such as Prisma . Comfortable writing and reviewing migrations, reasoning about transactions, and designing schemas that evolve safely. API Integration Depth: Real experience integrating third-party SDKs: handling webhooks, idempotency, retries, and asynchronous fulfillment. Problem-Solving Mindset: Collaborative, pragmatic, willing to challenge assumptions and surface tradeoffs before writing code. Passion for AI and High Agency: Genuine enthusiasm for AI products, and a desire to bring new techniques and tools into the team proactively. Creativity and Proactivity: You enjoy proposing features, finding creative solutions, and improving the user experience without being told to. A serious self-learner who adapts to new tools and platforms in days, not weeks. Nice to Have: Prior experience working on payment / subscription systems . Familiarity with monorepo tooling (pnpm workspaces, Turborepo, Nx). Experience with BigQuery and event-pipeline analytics. Familiarity with Tailwind and component-driven design systems. Knowledge of cloud platforms such as Google Cloud Platform (GCP) . Experience with feature-flag systems. Previous work on AI products or LLM-powered applications. Benefits High-Impact Role: Be a key player in a small, agile team building a greenfield projects with the potential to transform an industry. Modern Technology: Work with a cutting-edge, carefully selected tech stack with a focus on best practices. Growth & Learning: Gain deep experience in AI-driven applications, cloud-native architecture, and real-time systems. Stability & Vision: Enjoy the energy of a startup environment backed by the resources and stability of a large, successful company. Collaborative Culture: We value open communication, teamwork, and a shared passion for building exceptional products. Growth and career development At Leadtech, we prioritize your growth. Enjoy a flexible career path with personalized internal training and an annual budget for external learning opportunities. Work-Life balance Benefit from a flexible schedule with flextime and the option of working full remote or from our Barcelona office. Enjoy free Friday afternoons with a 7-hour workday, plus a 35-hour workweek in July and August so you can savor summer! Comprehensive benefits Competitive salary, full-time permanent contract, and top-tier private health insurance (including dental and psychological services). 25 days of vacation plus your birthday off, with flexible vacation options—no blackout days! Unique Perks If you wish to come, in our office in Barcelona you’ll find it complete with free coffee, fresh fruit, snacks, a game room, and a rooftop terrace with stunning Mediterranean views. Additional benefits include ticket restaurant and nursery vouchers, paid directly from your gross salary. Join us in an environment where you’re free to innovate, learn, and grow alongside passionate professionals. At Leadtech, you’ll tackle exciting challenges and be part of a vibrant team dedicated to delivering exceptional user experiences Sounds good? Apply now! We’re looking forward to getting to know you. Equal Employment Opportunity Employer: Leadtech is an Equal Employment Opportunity (EEO) Employer, which means we encourage applications from people with different backgrounds, interests, and personal circu