Mobile App Developer (React Native / Swift / Kotlin) — Founding Team at Happai

We’re looking for a high-quality mobile app developer to join the founding team at Happai — an early-stage tech startup on a mission to help people understand and improve their happiness through data.

Please note that we require you to submit your portfolio of previous mobile apps that you built and we will require a final in-person interview. Applicant must be U.S. based.

Please note: Applicants must be U.S.-based and able to complete a final in-person interview. A portfolio of previous mobile apps is required.

About Happai

Happai is building a beautifully designed, AI-powered app that helps people track their daily emotional states, uncover meaningful patterns, and gain personalized insights to improve emotional well-being and self-awareness.

Our team brings deep experience in entrepreneurship, product design, behavioral science, and marketing — including a founder who previously built a $1 billion company. We’re now channeling that expertise into creating a first-of-its-kind product that helps people understand what truly drives happiness, using a proprietary framework to analyze daily life patterns.

Our early MVP has already sparked strong “wow” reactions — and we’re ready to take it to the next level.

What You’ll Do

You’ll have end-to-end ownership of building Happai’s first full version and defining the product’s technical foundation. You’ll collaborate closely with the founder and designer to bring the already completed wireframes, screens, and algorithms to life.

Your responsibilities will include:

• Build and launch the first version of the Happai app (iOS + Android)
• Develop and integrate APIs (OpenAI, analytics, authentication, data storage)
• Architect the backend or collaborate with a backend engineer (FastAPI, Firebase, or similar)
• Deliver a delightful, smooth, and performant user experience
• Refine UI/UX details, animations, and onboarding flows with design
• Contribute to product direction, stack decisions, and company culture

Ideal Candidate

We’re looking for someone who’s already built and shipped high-quality consumer apps. You’re U.S.-based, hands-on, and passionate about creating apps that emotionally resonate with users.

You might be a great fit if you:

• Have shipped 2+ consumer apps end-to-end
• Bring 3–7 years of experience in mobile app development (React Native, Flutter, SwiftUI, or Kotlin)
• Have experience with AI/ML APIs (OpenAI, LangChain, etc.) — or are eager to learn fast
• Care deeply about clean architecture, scalability, and beautiful UX
• Have a strong understanding of data architecture, security, and privacy
• Possess an entrepreneurial mindset: take ownership, set standards, and build from zero
• Thrive in a fast-moving, zero-bureaucracy startup environment

Nice to Have:

• Are fluent in backend integration (Python FastAPI, Node.js, Firebase, Supabase)
• Have experience in mental health, well-being, or regulated data environments

Why Join Happai

• Be an early founding engineer with ownership and creative freedom from day one
• Work directly with the founder and shape the product’s direction
• Build something that genuinely helps people live happier, more self-aware lives
• Help define the culture of a startup built around deep work, learning, and joy

How to Apply

Send a quick note (plus links to your GitHub, portfolio, or apps you’ve built) to [email protected] or apply directly on LinkedIn.

Please include your portfolio — applicants without prior work samples will not be considered.