Senior Full-Stack Software Engineer

ZEN8 (Stealth Rebrand) / Connected Swim Training
📍 Lisbon | Full-time - Permanent 

Competitive salary based on experience, with stock options for high-impact results.

About ZEN8 Sports

In a world where cycling, running, and rowing have gone virtual, swimmers have been left behind. We’re changing that.

With over 20,000 athletes already training with our first product, we’ve proven the demand. Now we’re building the world’s first Connected Swim Training platform,  merging smart equipment, real-time performance data, and the thrill of gaming to make swim training accessible, engaging, and exciting for everyone.

We’re currently in stealth, finalizing our next-generation product and closing our Seed round to launch in the coming months. What we’re building will change how millions train, compete, and connect.

Role Overview

We’re looking for a Senior Full-Stack Software Engineer who thrives in fast-paced, high-growth environments and loves working across web and mobile platforms. 

You’ll help shape the architecture and user experience of our connected ecosystem, integrating real-time data, gameplay, and community features across web, iOS, and Android.

You’ll work closely with gameplay engineers, designers, and product leads to:

• Build and optimize scalable web and mobile applications using React, React Native, Node.js, and TypeScript.
• Integrate hardware data and real-time performance metrics into mobile and web experiences.
• Contribute to architectural decisions and development standards as we scale our platform.
• Ensure smooth deployment and performance in our AWS environment.
• Collaborate in-person at least 3 days a week, contributing to a creative and fast-moving product culture.

This role suits someone who’s hands-on, collaborative, and comfortable owning features end-to-end, from backend APIs to frontend interfaces and mobile delivery.

Key Responsibilities

• Design, build, and optimize web and mobile applications using React, React Native, Next.js, Tailwind CSS, Node.js, and TypeScript, ensuring responsive performance across devices.
• Develop backend APIs, real-time integrations, and data pipelines that deliver low latency and handle variable concurrent users.
• Architect solutions for scalability, reliability, and high availability, implementing redundancy and failover strategies where needed.
• Design and manage databases (SQL and NoSQL) to maintain data integrity, consistency, and high throughput.
• Implement Cloudflare, CloudFront, and S3 Origin configurations to improve load times, reduce latency, and ensure global content delivery performance.
• Protect user data and ensure compliance with GDPR and CCPA, applying secure-by-design principles across all systems.
• Monitor performance, latency, and resource utilization using observability tools to detect anomalies and optimize cost efficiency.
  Collaborate with designers and gameplay engineers to deliver seamless, intuitive user experiences backed by real-time feedback and stable backend performance.
• Use AI-assisted coding tools (Claude, GitHub Copilot, Cody) and automation platforms (n8n, Zapier, Make) to improve development speed and consistency.
• Work in a collaborative, hybrid setup, contributing in person from our Lisbon office at least 3 days a week.
• Experience working in a startup or small, fast-moving team environment. You thrive with autonomy, adapt quickly, and enjoy building things that don’t exist yet.

Required Skills

• 5+ years of experience in full-stack or backend-heavy roles.
• Strong proficiency in React, React Native, Node.js, and TypeScript.
• Proven experience delivering mobile apps for iOS and Android (including App Store / Play Store releases).
• Solid understanding of RESTful APIs, real-time communication, and websocket-based architectures.
• Solid experience with AWS (Lambda, API Gateway, DynamoDB, S3, CloudFront).
• Comfortable and proficient using AI-assisted coding tools (Claude, GitHub Copilot etc.).
• Experience with automation platforms such as n8n, Zapier, or Make to accelerate development and integrations.
• Strong focus on clean, maintainable, and scalable code.
• Apply Secure Software Development Lifecycle (SSDL) principles across all stages of development, ensuring security, privacy, and compliance are embedded from design to deployment.
• Maintain awareness of secure coding practices, threat modelling, and vulnerability mitigation throughout feature development.
• Proven ability to thrive in fast-paced, high-growth environments.

Additional Skills

• Experience with CI/CD pipelines for mobile and web (GitHub Actions).
• Familiarity with testing frameworks (Jest, Cypress, Playwright).
• Understanding of performance optimization and app analytics.
• Comfortable working with cross-functional teams including product, design, and hardware.

Nice to Have

• Experience with multiplayer, real-time gaming, or Unreal Engine integrations.
• Knowledge of BLE, IoT devices, or connected hardware ecosystems.
• Passion for triathlon, swimming, endurance sports, or human performance, or you deeply understand what drives athletes to train, improve, and stay consistent.
• Knowledge of game telemetry, analytics, or live balancing pipelines to support iterative tuning.

Experience optimizing mobile performance, packaging, and build pipelines for Android and iOS.