Senior Frontend Engineer

About the RoleThousands of engineers sign in daily to inspect traces, update prompts, and run experiments on an open-source LLM engineering platform — think Datadog, but for AI observability. Full LLM inputs and outputs can span tens of thousands of tokens. Your job: make that experience fast and intuitive.You love profiling React renders. You know when to virtualize, memoize, or restructure state. The data is massive — the interface should never feel like it is. This is a high-ownership, senior-level role on a small, remote-first European engineering team with meaningful cross-functional collaboration.What You'll DoBuild performant trace views — Own rendering of large LLM data: identify bottlenecks, optimize data loading, reduce re-renders so even the largest agent traces feel snappy.Own the React architecture — Shape how components are built, code is structured, and tests are written. Keep the codebase current with React Compiler and emerging patterns.Drive data visualization — Design and implement virtualized lists, grids, incremental loading, and data-heavy dashboards (cost, latency, evaluation results).Raise the quality bar — Champion automated testing across unit, integration, and end-to-end layers; conduct thorough code reviews and mentor peers.Collaborate cross-functionally — Work closely with product and backend engineers to ship features end-to-end across the full LLM development lifecycle.What We're Looking ForRequired:5+ years of frontend development experience shipping production web applicationsRight to work in the EU without visa sponsorship; ability to be on-site in Berlin approximately one week per monthStrong proficiency in JavaScript and TypeScriptDeep experience with React (or a comparable modern framework) and component-based architectureProven track record optimizing data-intensive UIs — virtualization, memoization, code-splitting, and profiling tools are second nature to youExperience building data visualizations and handling large client-side datasets (virtualized lists/grids, pagination, incremental loading)Solid automated testing background: unit, integration, and end-to-end (e.g., Jest, React Testing Library, Playwright, or Cypress)Comfortable working in small, remote, cross-functional engineering teams; confident mentoring peers and leading code reviewsFluent English communication skills; able to collaborate effectively across EU timezonesNice to Have:Familiarity with observability or analytics platforms; experience with ClickHouse, time-series data, or large analytical backendsOpen-source experience or contributions to public repositoriesBackground at companies working in AI/ML tooling, developer infrastructure, or data engineeringCompensation & BenefitsSalary: $90,000 – $160,000 USD annuallyEquity participation in a well-funded, high-growth AI infrastructure companySmall team — high autonomy, high ownership, direct impactRemote-first with regular in-person collaboration in Berlin (~once per month)LocationRemote (EU-based). The team is distributed across Germany, Austria, Switzerland, the UK, the Netherlands, France, Spain, Sweden, and Poland. You must be based in the EU with the right to work without sponsorship. Expect approximately one week per month on-site in Berlin, Germany.Visa sponsorship: Not available.Find more English Speaking Jobs in Germany on Arbeitnow