Mobile Frontend Engineer

Mobile Frontend Engineer Calibrex · New York, NY · In-person · 3 blocks from Grand Central. Compensation: $100k - $155k + bonus + meaningful equity At Calibrex, we build an AI voice coach for strength training powered by a magnetic wearable—like GPS for working out that tells you exactly what to do. We’ve shipped thousands of units worldwide, a sold-out pilot, backorders, and real power users. Now we’re building the mobile product that makes the coach feel essential every time someone trains. Important: How to get an interview Email subject: Your name | Desired RoleYour resume/LinkedIn with a brief note on a mobile product or technical problem you’ve owned.Include a 3-4 minute video recording (Loom or gdrive) introducing yourself and answering: "You’ve joined Calibrex with the goal of preparing our mobile experience for one million users. What are the first three things you would examine - in the codebase, product, or user journey - to assess our readiness, and why did you prioritize those three?" Submitting a video recording will significantly increase your likelihood of receiving an interview. We prioritize candidates who take this step because it gives us a much better understanding of how they frame problems, establish priorities, and communicate technical decisions. Don’t worry about production quality or delivering a perfectly polished answer. Thinking out loud is welcome - we want to understand how you think, not how well you present. What you’ll own The mobile experience that makes Calibrex feel indispensable in the gym: Expo/React Native screens, core workout flows, onboarding, interaction patterns, the design system, and the user-facing details that make coaching feel fast, clear, and trustworthy. You will own the experience of starting, executing, and reviewing a workout, not just implementing screens handed to you. You’ll work closely with the founder, who owns the overall architecture and system boundaries, and with our Product Systems & Integrations Engineer, who owns the underlying data, services, and integrations. Your job is to turn product feedback into fast, polished iterations and to use Codex as a serious force multiplier, not a substitute for engineering judgment. This is a high-agency role. One week you may be making the training flow feel effortless under load; the next you may be tightening onboarding, designing a better device-connection state, improving progress/history, or making an error state understandable in half a second. You should have - Strong production experience with React Native and Expo - Shipped consumer-facing mobile features end to end, from product detail to App Store / Play Store release - Excellent TypeScript and React fundamentals - Exceptional product and UI/UX instincts: you care about information hierarchy, responsive interaction, clear states, and the details that make an app feel trustworthy - Experience building or contributing to a coherent mobile design system and translating product intent into durable, reusable UI - Comfort integrating Firebase-backed features and collaborating across data, API, and native boundaries - A practical, disciplined workflow with Codex or comparable AI-assisted development tools; you can move quickly while reviewing, testing, and owning what ships Nice to have - Experience designing or implementing real-time, audio, BLE, wearable, sensor, or background-runtime experiences - Expo dev-client or native iOS/Android debugging experience - Experience with subscriptions, payments, HealthKit, or mobile analytics and experimentation - Startup experience on a small team - Experience with agentic loops, subagents, and second-brain systems Who you are Fitness-first and accountable. You lift weights regularly and take training seriously—this is not a perk box to check. You need to understand the product on your body, recognize when a cue or workout flow feels wrong, and care about the athletes we build for. You move fast, communicate clearly, and prefer owning outcomes over waiting for a perfectly scoped ticket. You have strong taste without being precious, seek direct feedback, and are comfortable getting your hands into unfamiliar parts of a system when a better user experience requires it.