Guillermo Sierra

About

Passionate Senior Mobile & Frontend Engineer with over 9 years of experience in building scalable applications with a strong focus on UX and performance. Experienced in Android (Java & Kotlin) and cross-platform development with React Native & TypeScript. Extensive experience in React, Next.js, GraphQL, Firebase, and backend technologies like Node.js & FastAPI. Thrives in startup environments, having co-founded and led engineering efforts in multiple ventures such as VetEasy, Divenamic, and Oralify, and contributed to high-impact projects at companies like Holded, Doctoralia, Fluz, and BodeBoca. Expertise includes Mobile Development (React Native, iOS, Android), Frontend Development (Next.js, React, TypeScript), State Management (Redux, Zustand, MobX), Backend & Databases (Node.js, FastAPI, Firebase), and crafting seamless user experiences and scalable UI components. Open to exciting opportunities to create, innovate, and push boundaries.

Experience

• Senior Mobile developer · dopelist.2025-05-01 –

  Built a unified React Native Web codebase for iOS, Android, and web, ensuring native-level performance and UX. Designed a robust User Store and route-guard system for guest vs. registered states, eliminating session bugs. Implemented real-time data sync with Firestore (and planned Postgres migration) via batched API writes and listeners. Orchestrated enrichment pipelines using GPT-4, Perplexity, Spotify API, and Google Places to produce “Dope” items with metadata, images, hashtags, and deep-links. Set up CI/CD with GitHub Actions & EAS, enforced ESLint/Prettier, added Jest unit tests, Detox E2E tests, and integrated Sentry. Partnered with Product & Design to iterate rapidly on core features—resulting in a working cross-platform POC in record time.

• Founder · Divenamic2024-06-01 –

  At Divenamic, we are passionate about underwater exploration and the well-being water provides. Our mission is to democratize access to the underwater world, promoting freediving, diving, and sustainable snorkeling as accessible and rewarding activities for everyone. Courses of Freediving and Snorkeling, High-Quality Equipment, Retreats and Experiences, Community and Education.

• Mobile developer · Laurel Gaming2024-11-01 – 2025-03-01
• Founder · Oralify2023-02-01 – 2024-12-01

  Express yourself. People ready to listen. Track your mood and emotions.

• Senior Mobile Developer · BODEBOCA2023-05-01 – 2024-02-01

  Development of the redesigned and updated version of the application and bug fixing.

• Senior mobile engineer · Fluz2023-05-01 – 2023-10-01
• Senior Frontend Developer · eevie2022-09-01 – 2023-05-01
• Senior Mobile Developer · Doctoralia España2021-07-01 – 2022-09-01

  Mobile developer - Doctors App

• Founder · PlanetMoji2020-11-01 – 2021-06-01

  Manager of Marketing & Product departments. eMoji games developed with React-Native-Web Mobile Web Android Tablet. React Native Web & React Native.

• CTO · VetEasy2021-03-01 – 2021-05-01

  Web & Mobile marketplace for Veterinaries with physical and online visit booking and scheduling. React-Native-Web, MobX, Firebase.

Education

• Universitat Politècnica de CatalunyaBachelor’s Degree, Computer Systems Networking and Telecommunications
• EPFLExchange Student, Computer Systems Networking and Telecommunications

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