Frontend Engineer

Withflex

United States Remote permanent

Posted: May 1, 2026

Job Description

About Flex

Flex was founded to solve a simple but costly problem: making it easy for health and wellness brands to accept HSA and FSA payments online. We're backed by First Round, Core VC, Rethink Capital power checkout for Equinox, Dermstore, Therabody, and Ultrahuman to name a few. For years, only giants like Amazon and Walmart could process these payments at checkout, leaving smaller merchants - and their customers - to deal with frustrating reimbursement paperwork.

Our technology verifies product eligibility in real time, handles split payments for eligible and non-eligible items, and can even issue Letters of Medical Necessity during checkout. With $150 billion in annual HSA/FSA spending potential, we’re giving brands the tools to unlock new revenue and making it easier for consumers to use the benefits they’ve earned.

About the Role

We’re looking for a Frontend Engineer to own developing our applications that merchants and consumers rely on everyday. You’ll work closely with backend engineers, design, and business stakeholders to ship seamless experiences that make HSA/FSA simple, accessible, and easy to use.

This is a role for someone who thrives in ambiguity, takes initiative, and is excited about building at an early-stage company.

Responsibilities (What You’ll Do)

• Lead frontend development using React across our multiple applications

• Ship high-quality experiences with a bias towards execution

• Partner with business stakeholders to ensure we’re addressing the needs of our merchants and consumers

• Own and improve our frontend architecture while identifying and closing experience gaps across our applications

• Collaborate on cross-functional projects that connect the full Flex experience, from consumer checkout to merchant analytics

• Contribute to a culture of learning, problem-solving, and operational excellence

Qualifications (Who You Are)

• You have 5+ years of experience in software development, with an emphasis on modern frontend technologies and building delightful user interfaces

• You have a strong understanding of modern web development best practices

• You’re resourceful, curious, and comfortable learning new tools quickly

• You thrive in fast-paced, dynamic environments and enjoy wearing multiple hats

• You’re collaborative and enjoy working across teams to solve problems

• You have an execution mindset and always keep the end user in mind

• You're proficient at leveraging AI tools to ship faster

Nice to Have

• Experience with building frontend applications with React

• Background in creating financial systems or tools leveraged by either merchants or consumers

Why Join Flex

• A mission-driven team making healthcare spending effortless

• Early-stage impact - your work will directly shape our growth and success

• Collaborative, high-trust, and transparent culture

• Competitive compensation and equity package

• Flexible, remote-friendly work environment

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