Build a Claude AI Agent From Scratch: No LangChain, No Frameworks, Just Python

Build a Claude AI Agent From Scratch: No LangChain, No Frameworks, Just Python LangChain has 87,000 GitHub stars and a reputation for being... a lot. Abstractions on abstractions. Fifteen ways to do the same thing. Documentation that's perpetually out of date. By the time you've debugged why your ConversationalRetrievalChain isn't calling tools correctly, you've forgotten what you were trying to build. Here's the secret: you don't need it. Claude's API natively supports tool use, multi-turn conversation, and structured outputs. The Anthropic SDK is clean. The mental model is simple. You can build a production-grade autonomous agent in ~150 lines of Python — and understand every line of it . This is that tutorial. We'll build it from scratch, including persistent memory that survives restarts. What We're Building A Claude agent that can: Use tools — math, web search, note-taking Reason across multiple turns — calls tools, observes results, continues reasoning Remember things — persisten