You're probably here because you use Cursor, Claude Code, or similar coding agents. They're impressive, but have you ever wondered how they actually work? Not the surface-level "they use LLMs" explanation, but the real mechanics: how do they manage context, execute tools, and maintain state across conversations?
That's what this series is about. We'll build a coding agent from scratch so you can see how these pieces fit together.
Why Build One Yourself?
When you understand how these agents work internally, everything changes:
You'll write better prompts because you know what the agent can and can't see. You'll debug issues faster because you understand the constraints. And honestly, it's just fascinating to see how something that feels like magic is actually a clever orchestration of tools, context management, and well-crafted prompts.
Plus, you might want to build something custom for your own workflow. Maybe an agent that understands your specific codebase patterns, or one that integrates with your team's tools. You can't do that if it's a black box.
What We'll Build
Our agent will have the key capabilities you've seen in tools like Cursor:
- Read and understand codebases
- Generate and modify code
- Use tools (file operations, grep, code execution)
- Stream progress updates to a frontend
- Manage conversations and context
- Route between different AI models based on the task
We'll cover the architecture, tool creation, prompt engineering, and state management. We'll use the @openai/agents SDK, Zod for validation, and support multiple model providers (Anthropic, OpenAI, Google, AWS Bedrock).
The goal isn't to replicate Cursor feature-for-feature. It's to understand the patterns that make these agents work, so you can build your own or just understand the tools you use every day.
What You Need to Know
You should be comfortable with:
- TypeScript and async programming
- Basic LLM API usage (you've called OpenAI or Anthropic's API before)
- Command line tools and file operations
If you've used coding agents and built basic web apps, you're ready. We'll fill in the rest as we go.
Let's Start
In the next article, we'll look at the agent class structure - how to organize your code so it can handle conversations, maintain state, and execute tools. Then we'll build our first tool and wire everything together.
Ready? Let's go.