CodeTrain serves as an educational platform tailored for engineers engaged in shipping AI projects, especially when they find it challenging to articulate every feature they have developed. By transforming a question, repository, or onboarding assignment into concise lessons comprised of two to six actionable steps grounded in actual code, it allows learners to actively engage by typing each line. While the tutor is responsible for designing the steps, executing the code, providing feedback on each attempt, and breaking down the steps further when a learner encounters difficulties rather than simply providing answers, this interactive approach fosters deeper understanding. The free tier facilitates Python execution directly in the browser via Pyodide, ensuring that no data is transferred off the user's machine, making it exceptionally cost-effective to operate. For more complex tasks, server-side sandboxes are utilized to manage shell and toolchain lessons. The infrastructure is supported by FastAPI hosted on Fly.io for the control plane, with a static front-end deployed on Cloudflare Pages, while authentication is managed through Clerk, and billing is processed via Stripe. Tutoring capabilities are primarily powered by Claude models, but the platform also accommodates custom keys for Anthropic, Bedrock, Vertex, OpenAI-compatible endpoints, and Ollama, allowing teams to leverage their existing infrastructure for inference. This flexibility ensures that organizations can optimize their learning tools while maintaining control over their resources.