Building with the Claude API

Building with the Claude API is the base layer for almost everything else you build on Claude. It covers the Messages API end to end — system prompts, multi-turn conversations, streaming responses, controlling output with stop sequences and structured/JSON output, and the token, temperature, and cost levers that shape every call. It also covers the building blocks the higher tracks assume you already know: tool use at the API level, prompt evaluation, and the basics of retrieval and agent loops. Get this right and the agent, RAG, and eval tracks become a matter of composition rather than guesswork.