Senior Fullstack Developer (Blockchain)

We are Merlin Digital Partner , a leading IT & Digital talent acquisition consultancy with over 10 years of experience. We have scaled industry giants such as Wallapop, Glovo, Banc Sabadell, and Sulzer, among others. Focused on humanizing and streamlining recruitment, our mission is to transform companies by connecting them with top-tier talent. We pride ourselves on diving deep into our partners' realities, understanding not just their technical needs, but their core essence.

One of our rapidly growing partners is looking for a Senior Full Stack Developer . They are a deep-tech company specializing in the certification and verification of digital data using Blockchain technology . Their platform ensures information authenticity, integrity, and traceability, with key applications in digital identity, regulatory compliance, and sensitive data management.

The Mission

You will design and build end-to-end digital applications based on an API-first architecture , ensuring seamless data management, system integration, and a robust user experience. This role combines advanced backend capabilities with frontend development and a strong focus on data architecture.

Key Responsibilities

Architecture & Backend

• Design and implement scalable APIs (REST / GraphQL) using Node.js.
• Define and evolve data models in Supabase (PostgreSQL).
• Model relational databases (normalization, integrity, optimization).
• Build modular, maintainable backend services.
• Manage authentication and access control (JWT, RBAC).

Frontend & Experience

• Develop high-performance interfaces using React / Next.js or similar stacks.
• Integrate APIs ensuring consistency and efficiency in data consumption.
• Define frontend patterns (state management, caching, SSR).
• Collaborate on product-oriented UX/UI decisions.

Integration & Data

• Integrate external systems (APIs, OAuth, IoT, third-party services).
• Design data flows (ETL, webhooks, synchronization).
• Guarantee data consistency and quality across systems.

Quality & Deployment

• Apply development best practices (Testing, CI/CD).
• Containerization and deployment (Docker, Cloud environments).
• Document APIs and architectural decisions.

Tech Stack

• Node.js
• Supabase
• PostgreSQL
• React / Next.js
• Docker
• REST / GraphQL
• CI/CD

What we are looking for

• +3-5 years of experience as a Full Stack Developer.
• Expertise in Node.js (Express / NestJS).
• Proficiency in React / Next.js or similar frameworks.
• Hands-on experience with PostgreSQL / Supabase .
• Solid knowledge of relational data modeling.
• Proven experience in API design.
• Familiarity with Git, cloud environments, and CI/CD workflows.

Nice to have

• Blockchain Experience: Familiarity with Ethereum, smart contracts, and digital identity (SSI).
• Architectural Knowledge: Experience with distributed architectures or microservices.
• Sensitive Data Management: Background in handling highly secure data (Healthtech, Fintech, or Identity Management).
• Headless CMS/Platforms: Experience integrating with headless solutions like Directus or similar tools.
• AI & Analytics: Previous experience in projects involving AI components or data analytics.

Benefits

• Location: Barcelona
• Salary Range: €50,000 – €55,000
  • We are open to considering candidates outside this range (both Junior and Senior profiles) depending on technical expertise and the value brought to the role, as the team is actively expanding.
• Remote-Friendly: You will be able to work remotely, with occasional in-person meetings in Barcelona.
• Core Team Impact & Career Plan: You will join the core of an innovative project in its high-growth phase. This offers the opportunity to build your own career