Build Your First Agent

By the end of this lesson you will be able to move from an idea to a working agent prototype quickly, using the simplest effective patterns. The core ideas are rapid prototyping with SDKs, keeping it simple, and carefully designing your Agent-Computer Interface (ACI). Frameworks like the Claude Agent SDK handle the underlying loop and context management so you focus on the logic. Engineering the ACI means writing clear, well-documented tool descriptions the model can easily understand, just as you would for a human developer. Worked example: a simple weather agent. You write a system prompt telling the agent it is a meteorologist, provide a single HTTP tool that fetches weather data with a clear description of its parameters, choose a capable Claude model (such as Sonnet), and let the SDK handle the autonomous back-and-forth when a user asks about the weather. Practice task: design your first agent by writing its system prompt and drafting clear descriptions for the two tools it will use.