Senior Frontend Engineer

Thousands 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., * Build 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.

• 5+ years of frontend development experience shipping production web applications
• Right to work in the EU without visa sponsorship; ability to be on-site in Berlin approximately one week per month
• Strong proficiency in JavaScript and TypeScript
• Deep experience with React (or a comparable modern framework) and component-based architecture
• Proven track record optimizing data-intensive UIs - virtualization, memoization, code-splitting, and profiling tools are second nature to you
• Experience 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 reviews
• Fluent English communication skills; able to collaborate effectively across EU timezones

Nice to Have:

• Familiarity with observability or analytics platforms; experience with ClickHouse, time-series data, or large analytical backends
• Open-source experience or contributions to public repositories
• Background at companies working in AI/ML tooling, developer infrastructure, or data engineering

• Salary: $90,000 - $160,000 USD annually
• Equity participation in a well-funded, high-growth AI infrastructure company
• Small team - high autonomy, high ownership, direct impact
• Remote-first with regular in-person collaboration in Berlin (~once per month)