Freelance Full-Stack Web App Developer at Mindrift · Barcelona

Mindrift is looking for skilled Full-Stack Web App Developers (JavaScript/TypeScript + Python or Node) to join the Tendem project (https://tendem.ai/) and build interactive browser-based applications for real-world use cases.

In this role, you'll apply your full-stack engineering expertise to design, build, and maintain functional, robust, and user-friendly web applications. This part-time remote opportunity is ideal for professionals with hands-on experience in modern frontend frameworks, backend APIs, databases, and shipping interactive web products end-to-end.

What We Do

The Mindrift platform connects specialists with innovative technology projects. Our mission is to help develop high-quality AI technologies by combining real-world expertise from professionals across the globe with advanced AI development efforts.

About the Role

This is a freelance role for a Tendem project. As a Full-Stack Web App Developer, you'll design, build, and refine browser-based applications with real logic, state, persistence, and user input — from habit trackers and budgeting tools to internal dashboards, mini-SaaS tools, and AI-powered apps. You may also work on standalone Python applications and data-processing scripts that sit alongside or behind these products.

Key Responsibilities

• Build interactive web applications with frontend (React, Next.js, Vue, or similar) and a backend API (Python/FastAPI/Flask or Node/Express).
• Design and implement data models, schemas, and persistence layers using SQL (PostgreSQL, SQLite) or NoSQL stores.
• Implement authentication, sessions, and basic role-based access where needed.
• Integrate third-party APIs and AI/LLM services (OpenAI, Anthropic, or similar) into product features.
• Handle state management, user input validation, error states, and loading states cleanly.
• Build standalone Python tools and scripts where required by the task (data processing, API clients, lightweight backend utilities).
• Review, debug, optimize, and refactor full-stack applications to improve correctness, security, performance, and maintainability.
• Write clear, testable code and debug end-to-end issues across frontend, backend, and database.

Educational qualifications

• At least 3 years of relevant experience in full-stack web development or shipping interactive web applications (required).
• Bachelor's or Master's Degree in Computer Science, Engineering, Information Technology, or related technical fields is a plus.

Academic and/or Professional Experience

Candidates should have a strong foundation in full-stack web development, modern frontend frameworks, backend architecture, and building interactive browser-based applications end-to-end. We are looking for specialists who can confidently work across frontend, backend, databases, and APIs, design robust application logic, and build production-ready web applications. Strong problem-solving skills, attention to detail, and the ability to independently architect and ship complete features are essential.

Technical Skills (Essential)

• Strong command of JavaScript/TypeScript and at least one modern frontend framework (React, Next.js, Vue, Svelte, or similar).
• Solid backend experience in Python (FastAPI, Flask, Django) and/or Node.js (Express, NestJS).
• Hands-on experience with relational databases (PostgreSQL, MySQL, SQLite) and basic schema design.
• Experience implementing REST APIs, request validation, error handling, and authentication flows.
• Familiarity with deployment platforms (Vercel, Netlify, Render, Fly.io, Railway, or similar).
• Experience integrating LLM APIs or other AI services into product features is a strong plus.
• Comfortable with version control (Git) and basic testing practices.

Additional requirements

• Strong attention to detail and commitment to building working, robust products — not demos.
• Self-directed work ethic with the ability to architect, build, and ship features independently.
• Portfolio of shipped web applications (required).
• English proficiency: Upper-intermediate (B2) or above (required).

Project time expectations

For this project, tasks are estimated to require around 10–20 hours per week during active phases, based on project requirements. This is an estimate, not a guaranteed workload, and applies only while the project is active.

Compensation

On this project, contributors can earn up to $50 per hour equivalent, depending on their level and pace of contribution.

Compensation varies across projects depending on scope, complexity, and required expertise. Please note that other projects on the platform may offer different earning levels based on their requirements.

Why this freelance opportunity might be a great fit for you?

• Work fully remote on your own schedule with just a laptop and stable internet connection.
• Apply your expertise to real-world technology projects while gaining experience building high-quality solutions for a global platform.
• Participate in performance-based bonus programs that reward high-quality work and consistent delivery.