Senior Frontend Engineer

About the Role

Thousands of engineers rely on this platform daily to inspect traces, iterate on prompts, and run experiments across their LLM applications. Full LLM inputs and outputs can span tens of thousands of tokens — your job is to make that experience fast, intuitive, and effortless.

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. As a Senior Frontend Engineer, you'll own the performance and architecture of a complex, data-intensive web application used at scale by AI engineers worldwide.

What You'll Do

• Build performant trace views — Own the rendering of large LLM data: identify bottlenecks, optimize data loading, and 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.
• Design and implement data visualizations — Build rich, interactive charts and tables that surface cost, latency, and quality signals from high-volume analytical data.
• Drive frontend quality — Write and advocate for unit, integration, and end-to-end tests. Establish standards for code reviews and mentor peers across a small, cross-functional team.
• Collaborate cross-functionally — Work closely with product, design, and backend engineers to ship features end-to-end across the LLM development lifecycle — tracing, evaluation, prompt management, experiments, and more.
• Contribute to open source — A significant portion of the codebase is public; your work will be seen and used by a large developer community.

What We're Looking For

Required:

• 5+ years of frontend development experience building production web applications
• Strong proficiency in JavaScript and TypeScript
• Deep experience with React (or a comparable modern framework) and component-based architecture
• Proven track record optimizing web performance for large, data-intensive UIs — virtualization, memoization, code-splitting, and profiling tools
• Experience building data visualizations and handling large client-side datasets (virtualized lists/grids, incremental loading, pagination)
• Solid testing practices: unit, integration, and end-to-end (e.g. Jest, React Testing Library, Playwright, or Cypress)
• Experience in small, remote, cross-functional engineering teams; comfortable mentoring peers and conducting code reviews
• Fluent English communication skills; able to collaborate effectively across EU time zones
• Right to work in the EU without visa sponsorship and ability to be on-site in Berlin approximately one week per month

Nice to Have:

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

Location

This is a hybrid remote role based in the EU. The team is distributed across Germany, Austria, Switzerland, the UK, the Netherlands, France, Spain, Sweden, and Poland. You'll be expected to visit the Berlin office approximately one week per month. Visa sponsorship is not available — you must have the right to work in the EU.

Compensation & Benefits

• Salary: €90,000 – €160,000 per year, depending on experience and location
• Equity participation
• Flexible remote-first work environment with regular in-person team gatherings
• Work on a widely adopted open-source product with a large, engaged developer community
• High ownership and direct impact in a small, senior team at an early stage backed by top-tier investors