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Sebastian Crossa

Sebastian Crossa

Full-stack web engineer building AI agents and functional products

sebcrossa
New York City, New York
Joined June 2025

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Summary

Sebastian Crossa is a driven full-stack web engineer and entrepreneur specializing in AI. He is the Co-Founder and CTO of ZeroEval, a Y Combinator-backed startup focused on developing tools for optimizing and evaluating AI agents. His work at ZeroEval centers on creating 'calibrated LLM judges' that improve over time and an 'Autotune' system for automatic evaluation and prompt optimization based on human feedback. sebastiancrossa+2
With a strong background in early-stage startups, Sebastian has served as Founding Engineer at Micro (backed by a16z), where he built the core technology for an email-powered all-in-one tool, and as a Software Engineer at Launch House. He was also an early engineer at Atrato (YC W21). His experience spans developing core products, optimizing processes, and scaling user engagement. sebastiancrossa+3
Sebastian demonstrates a commitment to open-source contributions and community involvement. As an Open Source Fellow at Major League Hacking, he contributed to the AWS Amplify CLI, working on bug fixes and developing new features like resource tagging. This experience also honed his skills in working effectively within distributed teams. amazon+1
He possesses a diverse technical skill set including User Experience Design (UED), CLI development, Amazon Web Services (AWS), Front-End Development, and Full-Stack Development. He is passionate about building functional products and contributing to high-impact projects, as evidenced by his personal website statement and work on projects like LLM Stats, which garnered significant user adoption. sebastiancrossa+2

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