Senior Software Engineer, Frontend

LMArena is the open platform for evaluating how AI models perform in the real world. Created by researchers from UC Berkeley’s SkyLab, our mission is to measure and advance the frontier of AI for real-world use.

Millions of people use LMArena each month to explore how frontier systems perform — and we use our community’s feedback to build transparent, rigorous, and human-centered model evaluations. Leading enterprises and AI labs rely on our evaluations to understand real-world reliability, alignment, and impact. Our leaderboards are the gold standard for AI performance — trusted by leaders across the AI community and shaping the global conversation on model reliability and progress.

We’re a team of researchers, engineers, academics, and builders from places like UC Berkeley, Google, Stanford, DeepMind, and Discord. We seek truth, move fast, and value craftsmanship, curiosity, and impact over hierarchy. We’re building a company where thoughtful, curious people from all backgrounds can do their best work. Everyone on our team is a deep expert in their field — our office radiates excellence, energy, and focus.

LMArena is seeking an experienced Senior Frontend Product Engineer to lead the design and development of intuitive, AI-focused user experiences across our platform. You’ll be responsible for owning features from proposing technical approaches and implementing core UI/UX flows, to deploying new functionality and tracking its impact through analytics. This role is ideal for someone who combines strong frontend craft with backend thinking, thrives on building polished user interfaces, and is excited to shape how people interact with cutting-edge AI models.

• Lead development of UI and application logic for our chat interface using React and Next.js

• Craft intuitive, accessible, and responsive user experiences that feel delightful across devices

• Collaborate closely with design to maintain and extend a cohesive visual language and component system

• Implement A11y accessibility standards and internationalization (i18n) support for a global audience

• Expand backend data structures and business logic to support new frontend features

• Plan and integrate analytics to measure user engagement, adoption, and product performance

• Visualize feature performance and usage metrics through dashboards and internal tooling

• Own the full feature lifecycle—from technical scoping to deployment and iteration based on insights

• 5+ years of experience in software engineering, with a focus on full-stack or frontend product development

• Deep experience building accessible, responsive React/Next.js interfaces in production

• Strong CSS fundamentals and familiarity with utility-first frameworks like Tailwind

• Experience working with modern component systems such as ShadCN or similar design systems

• Comfortable building and integrating backend APIs (bonus if you've worked with HonoJS or lightweight frameworks)

• Proficient with relational databases such as Postgres, and how to extend schemas to support new features

• Familiarity with testing practices and tools like Vitest (or similar testing frameworks)

• Experience integrating analytics tools and using product metrics to guide iteration

• Clear communicator and strong collaborator across design, product, and engineering teams

• Bonus: Experience building real-time or AI-driven UIs, or shipping features for technical audiences

• NextJS

• Tailwind

• ShadCN

• HonoJS

• Postgres

• Vitest

• We offer competitive compensation and equity aligned to the markets where our team members are based. The base salary range will depend on the candidate’s permanent work location.

• Comprehensive health and wellness benefits, including medical, dental, vision, and additional support programs.

• The opportunity to work on cutting-edge AI with a small, mission-driven team

• A culture that values transparency, trust, and community impact

Come help build the space where anyone can explore and help shape the future of AI.

LMArena provides equal employment opportunities (EEO) to all employees and applicants for employment without regard to race, color, religion, sex, national origin, age, disability, genetics, sexual orientation, gender identity, or gender expression. We are committed to a diverse and inclusive workforce and welcome people from all backgrounds, experiences, perspectives, and abilities.