15.4 The claude-code-from-scratch Project
The claude-code-from-scratch project provides a runnable minimal implementation (~1,300 lines of core code) to help you:
- Understand core mechanisms: Without being overwhelmed by 512K lines of code, focus on the 7 essential components
- Hands-on experimentation: Modify loop logic, add new tools, adjust system prompts
- Learn design decisions: Understand why each component exists and why it's implemented this way
- Progressive building: Gradually add features from the minimal version, experiencing the value of each layer of complexity
The project also provides dual backend support (Anthropic native + OpenAI-compatible API), meaning you can use it to connect to virtually any LLM backend. Switch to any OpenAI-compatible endpoint via the --api-base parameter.
Customization Advice: If you want to build your own agent based on this minimal implementation, the system prompt template (src/system-prompt.md) is the highest-leverage customization point. Modifying behavioral instructions, adding domain-specific knowledge, adjusting tool usage preferences -- these zero-cost text modifications can significantly change the agent's behavior.
For detailed step-by-step tutorials, please refer to the claude-code-from-scratch documentation.