Senior Frontend Engineer

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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-s.