Neon

Why building eval platforms is hard — Phil Hetzel, Braintrust

Apr 28, 2026 · 25:39

Phil Hetzel of Braintrust argues that building eval platforms for AI agents is a data systems problem, not just a UI one, because LLMs have extreme variability and agent traces are semi-structured, high-volume, and large. He describes four maturity stages: simple spreadsheet with a for loop, a custom vibe-coded UI with a database, an experimentation playground for non-technical users, and finally a flywheel connecting offline evals with production observability. The core challenge is the data layer—traces can be 10-20 MB per span, requiring low-latency ingestion, aggregate analysis, and full-text search, which traditional databases cannot handle. Future platforms must surface unknown unknowns via topic modeling, support agent-to-agent interactions, and integrate automatic tracing through AI proxies. Braintrust addresses these with a custom data platform that separates hot and cold storage and enables SQL queries directly on traces.

Using OSS models to build AI apps with millions of users — Hassan El Mghari

Jul 15, 2025 · 18:47

Hassan El Mghari, a software engineer at Together.ai, explains how he builds open source AI apps that attract millions of users, including roomGPT.io (2.9 million users), restorePhotos.io (1.1 million), Blinkshot.io (1 million visitors), and LlamaCoder.io (1.4 million visitors). He details his simple four-step tech stack: user input, a single API call to an open source model on Together.ai, storing results in a database, and displaying output. His process emphasizes keeping ideas simple enough to describe in five words, spending 80% of time on UI, launching early, and incorporating the latest models like Fluxionel for virality. He advises naming apps with short, memorable names, making them free and open source to encourage sharing, and iterating rapidly—most apps fail, but the key is to keep building. He funds compute through sponsorships from Together.ai and partners like Neon and Clerk, which provide free services for his open source projects.