Senior Full Stack Developer, AI

Leadtech Group

Full Stack Developer for A.I technology products delivering seamless user experiences. Collaborating with teams to build and scale AI-driven applications.

Posted 6/1/2026full-timeRemote • 🇪🇸 SpainSeniorWebsite

Tech Stack

Tools & technologies

BigQueryCloudGoogle Cloud PlatformJavaScriptNext.jsNode.jsPostgresPythonReactTypeScript

About the role

Key responsibilities & impact

As part of the Development team as a Full-Stack Developer, you will be instrumental in building and scaling our platforms and products.
You will work across our entire A.I technology stack to deliver a seamless and powerful user experience.
You will be joining projects with a shipping fast approach and a modern tech stack.
Design, implement, and maintain RESTful APIs with NextJS/Express to manage user authentication, data processing, and orchestrate analysis workflows.
Model Context Protocol (MCP) Knowledge Agents with Claude SDK: to Build AI agents access to real-time data, APIs, and tools Create AI Agents that can actually take actions, Combine the reasoning power of LLMs with real-world integration.
Build AI Agents with LangGraph + LangFuse that can handle multi-step reasoning, Create workflows where AI agents collaborate or hand off tasks to other agents. Maintain conversation state and context across interactions and Handle complex decision trees and conditional logic.
Develop and maintain features on both our React frontend and Node.js (NextJS) backend.
Build intuitive user interfaces using TypeScript, Vite, React and our UI component library, enabling users to upload media, manage their analyses, and interact with our web delivered product.
Integrate our platform with various external services like Payment Service Providers and APIs, and handle incoming webhooks for processing asynchronous tasks.
Collaborate closely with AI product managers and AI specialists to translate complex requirements into robust, scalable features expressed in AI design prompts.
Contribute to database schema design and write migrations for our PostgreSQL & BigQuery databases.
Knowledge of GCP to Collaborate with the team on application deployment and help maintain our cloud infrastructure on Google Cloud Platform.

Requirements

What you’ll need

Extensive experience with the Python framework
Deep API Integration experience with 3rd Party vendors. Being able to work with multiple types of SDK to integrate into our products quickly.
A serious self-learner and someone that adapts to new tools and platforms very quickly and adapts it into their day to day workflow in days.
TypeScript Proficiency: You are highly proficient in TypeScript and its application in both frontend (React) and backend (Node.js) environments.
Frontend Expertise: Strong experience with React and modern state management, including Hooks and the Context API.
Backend Expertise: Solid experience building and consuming REST APIs with Node.js and NextJS or Express.
Database Skills: Experience with like PostgreSQL, and working with an ORM or query builder.
Knowledge of LangGraph, LangChain, LangFuse,
Problem-Solving Mindset: You are a collaborative problem-solver, eager to take on new challenges and contribute to a fast-paced development cycle.
Passion for AI: A genuine passion and awareness for artificial intelligence and a strong desire to build products that leverage its capabilities to solve real-world problems. and bring those new discoveries to our product Portfolio.
Very High Agency: in consultation with a Product Owner and the Engineering Manager, you must work with autonomy with a large degree of freedom to implement the business vision.
Creativity and Proactivity: You have a passion for building great products, are eager to propose new features, and enjoy finding creative solutions to improve the user experience.
Nice to Have: Previous experience working on projects involving AI, machine learning, or interacting with large language models (LLMs).
Familiarity with UI component libraries.
Knowledge of cloud platforms like Google Cloud Platform (GCP).

Benefits

Comp & perks

High-Impact Role: Be a key player in a small, agile team building a greenfield project 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.

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Hard Skills & Tools

PythonTypeScriptReactNode.jsNextJSExpressPostgreSQLBigQueryRESTful APIsAPI Integration

Soft Skills

problem-solvingcreativityproactivityself-learningadaptabilitycollaborationautonomypassion for AIcommunicationfast-paced development