Backend Engineer - Platform Core

Backend Engineer (Golang) – Platform Core Location: Remote, European time zones, Full-time, Permanent About FullEnrich: Every go-to-market motion runs on data, but no single provider has ever had complete coverage. We solve that problem with waterfall enrichment: instead of relying on a single data source, we orchestrate 20+ premium providers around the world, automatically querying them until we find the best available contact information. The result is industry-leading coverage and data quality, helping sales and GTM teams connect with the right people faster. What started as a better way to find emails and phone numbers has grown into a broader vision: becoming the trusted B2B data layer powering modern revenue teams and AI-driven workflows alike. Today, more than 5,000 customers, including companies like AWS, Deel, HubSpot, Clay, and Artisan, trust us to power their prospecting and enrichment. Founded in Paris and now headquartered in San Francisco, we're a team of 50+ people across the US, Europe, LATAM, and Israel, growing quickly and building with speed, ownership, and ambition. That's where you come in. About the Role: At the heart of FullEnrich is our waterfall engine. It's the system responsible for deciding which data providers to call, in what order, under which conditions, and what happens when something fails. It works well today, but what we're building next is significantly more ambitious. We're evolving the engine to become far more flexible and configurable, supporting account-specific requirements, dynamic routing based on different optimization goals, and seamless integration of new providers and behaviors without introducing unnecessary complexity. This is a foundational part of our product, and getting the architecture right is critical to how we scale. We're looking for an experienced Backend Engineer who enjoys solving complex infrastructure challenges and taking ownership of the systems behind them. If you've built high-throughput routing systems, designed multi-provider orchestration layers, or worked on infrastructure that needs to adapt to different customers and use cases, this is exactly the kind of challenge you'll be taking on. What You'll Do: Own and evolve our core routing engine: Take ownership of provider selection, fallback logic, load balancing, and queue management. Our waterfall currently operates as a modular Go monolith, and you'll help evolve it to support account-level customization at scale without introducing unnecessary complexity. Build and improve provider integrations: Design how we connect to and manage third-party data providers, focusing on rate limiting, reliability, and observability. This includes supporting external provider credentials, configurable provider ordering, and well-defined fallback behavior when providers are unavailable. Develop intelligent routing capabilities: Build the logic that dynamically selects providers based on different optimization objectives, including speed, coverage, compliance, and intelligent load balancing, while managing rate limits effectively. Design scalable multi-tenant architecture: Develop the foundations for sub-accounts, customer-specific credit pools, and endpoint-level configuration, ensuring the engine remains flexible, scalable, and maintainable. Build composable verification workflows: Integrate validity and compliance checks into the enrichment pipeline as configurable steps, allowing results to be independently verified regardless of their original data source. Strengthen our core architecture: Improve and refactor existing systems as we scale, applying strong engineering practices to keep our codebase clean, understandable, reliable, and easy to maintain. Shape technical decisions: Work closely with our engineering leadership to translate product requirements into thoughtful architectural solutions, balancing immediate needs with long-term scalability. What Success Looks Like In you