Senior Full Stack AI Native Developer

About the role

Leadtech Group builds and scales digital products used by millions of people worldwide; within the group, MAU by Leadtech focuses on subscription-based apps and digital products. As a Senior Full Stack AI Native Developer in the Development team, you will build and scale platforms and products across the entire AI technology stack, joining projects with a fast-shipping approach and a modern tech stack. The role is offered with the option to work fully remote or from the Barcelona office.

Key responsibilities

• Design, implement and maintain RESTful APIs with NextJS/Express for authentication, data processing and analysis workflows.
• Build AI agents with MCP, Claude SDK, LangGraph and LangFuse that access real-time data, APIs and tools, and handle multi-step reasoning and complex decision trees.
• Develop features on the React frontend and Node.js (NextJS) backend, including media uploads and analysis management.
• Integrate the platform with payment providers and APIs, and handle incoming webhooks for asynchronous tasks.
• Work with AI product managers and AI specialists to turn requirements into scalable features expressed in AI design prompts.
• Contribute to database schema design and migrations for PostgreSQL and BigQuery.
• Help deploy applications and maintain cloud infrastructure on Google Cloud Platform.

Required profile

• Extensive experience with the Python framework and deep API integration with third-party vendors via multiple SDKs.
• Highly proficient in TypeScript, with strong React and modern state management (Hooks, Context API).
• Solid experience building and consuming REST APIs with Node.js, NextJS or Express.
• Experience with PostgreSQL and an ORM or query builder.
• Knowledge of LangGraph, LangChain and LangFuse; familiarity with UI component libraries is a plus.
• Previous AI, machine learning or LLM project experience is a plus.
• Autonomy in implementing the business vision with a Product Owner and Engineering Manager.

Required skills

• TypeScript, React, Node.js, NextJS, Express
• PostgreSQL, BigQuery, GCP
• LangGraph, LangChain, LangFuse, MCP, Claude SDK

What we offer

• Flexible schedule with flextime, full remote or office work, and free Friday afternoons; 35-hour week in July and August.
• Full-time permanent contract, competitive salary and private health insurance (dental and psychological).
• 25 days of vacation plus a day off on your birthday, with flexible vacation options.
• Internal training and an annual budget for external learning.
• In the Barcelona office: free coffee, fruit and snacks, game room, rooftop terrace, ticket restaurant and nursery vouchers.