> Markdown version of [/jobs/ext/3024404-principal-fullstack-engineer](https://www.wearedevelopers.com/jobs/ext/3024404-principal-fullstack-engineer). Every page supports `.md` or `Accept: text/markdown`. Links point to the HTML versions so they work for humans too. Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md). --- # Principal FullStack Engineer - **Company:** Experis - **Location:** Spain (Remote available) - **Contract:** Permanent contract - **Skills:** Query Performance, PostgreSQL, Node.Js, Query Optimization, Redis, Digitalocean, Next.js, Systems Integration, TypeScript, ReactJS, Database Optimization, Backend, Data Layers, Material UI, Graphql, Front End Software Development - **Published:** September 22, 2026 - **Apply:** https://www.experis.es/es/oferta-de-empleo/740583/principal-fullstack-engineer/madrid ## About the Role Must have * Ability to own a product end to end. We care about demonstrated depth and ownership, not the number. * Strong TypeScript on both sides: React/Next.js on the frontend and Node.js on the backend. * Solid PostgreSQL: schema design, query optimisation, and migrations, with the instinct to reason about performance under high write volume. * Experience maintaining a component library or design system, not just consuming one. * A genuine end-to-end ownership mentality, from technical design through implementation to deployment, and the pragmatism to ship a good solution rather than chase a perfect one. * Comfortable making product-facing decisions with limited spec, and translating a rough founder request into something shippable. * Strong written communication. We are async-first and clarity matters. * Comfortable using AI tools such as Claude as part of your daily workflow to increase speed and quality. * Experience in a small team where you wear multiple hats. Nice to have * Ad tech or e-commerce background. * GraphQL. * Fastify or similar Node.js frameworks. * Redis. * DigitalOcean App Platform or Vercel. ## Description A small, experienced group of engineers, a designer and a founding team that stays close to the product. Engineers own features end to end, work closely with design, and have a direct line to the decisions that matter. We use Claude Team Enterprise as a core part of how we work and expect everyone on the team to do the same We are a lean team of senior full-stack engineers, and this role sits at the top of that group as the person we rely on when something is hard, ambiguous, or nobody else has the context. This is a hands-on role, roughly 90% coding. We are not looking for a pure architect or someone who wants to direct from a distance. We are looking for someone who is deep in the codebase every day, ships features themselves, and makes pragmatic calls that move the product forward. You will also help shape technical direction, work directly with our founders to turn product ideas into scoped, shippable work, and raise the bar for the whole team. What you will own * End-to-end feature delivery across the whole stack: Next.js frontend, Node.js backend, PostgreSQL, and deployment. * Our real-time analytics dashboard, which gives merchants a single view of ad performance across every channel and platform. * Our UI component library: long-term ownership of how we build and maintain frontend consistency across the product. * Infrastructure and reliability: database optimisation, Redis stability, observability, and integrations with ad platforms including Meta, Google, Bing, and Taboola. * Keeping the product's data layer fast and reliable as we grow: schema and query performance, sensible aggregation, and reporting that holds up under load. 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