Senior Full stack developer Next.JS/Node.JS

Company Description: MestrIA is a service platform providing end-to-end document intelligence solutions tailored for legal and financial teams across Europe---including law firms, banks, real estate servicers, debt recovery specialists, and insurers, insurance companies, transportation industry..
While generic AI tools struggle with complex, jurisdiction-specific documentation, MestrIA delivers complete, end-to-end workflows: automating data extraction from judicial and financial files, accelerating due diligence, and delivering confidence-scored, audit-ready precision.
Backed by EU funding and based in Spain, our platform operates on GDPR-compliant, EU-based infrastructure aligned with the EU AI Act and is actively expanding across Europe with live production deployments.
As an early-stage Senior Full-Stack Product Engineer, you will shape both our core end-to-end service platform and our engineering foundations from day one. Working directly with the founders and cross-functional teams, you'll translate complex legal and financial workflows into secure, scalable, and maintainable software.
Build responsive front-end interfaces, scalable APIs, database workflows, and real-time processing status pipelines that deliver seamless client solutions.
Optimize PostgreSQL models, AWS infrastructure, CI/CD, and monitoring with privacy-by-design principles (GDPR / EU data residency).
Backend: Python (FastAPI) and/or Node.js; Frontend: TypeScript, React, Next.js, HTML, CSS.
Data: PostgreSQL (relational modeling, migrations, performance tuning).
Cloud & DevOps: AWS (ECS/Fargate, App Runner, S3, CDK/IaC), Docker, CI/CD, and production monitoring.
Skilled in integrating 3rd-party APIs, AI services, file upload flows, and background processing.
Awareness of GDPR, EU data-residency requirements, and secure handling of sensitive data.
Professional fluency in English. Spanish or another EU language is a plus.
Background: Bachelor's degree in CS/Engineering (or equivalent hands-on experience / final-year students with strong production work).
Impact: High ownership in an early-stage, fast-growing startup backed by EU funding.
Hybrid working model based in Madrid, A Coruña, or Barcelona with work-from-home flexibility.