Getting Started with Agentic Coding with OpenAI's Codex

The Fastest Way to Get Started With Agentic Coding

If you have wanted to start agentic coding and don’t know where to start, this is the place for you. There are so many coding agents now that it’s confusing where to start and what offers you the best capabilities. As we speak now, there are agentic interfaces that have already shuttered in this competitive market, but there are many standouts that are at their peak. We are going to use OpenAI’s Codex, learn how to use the tool, and then take a coding project from idea to a design, and then have Codex implement it.

Your agentic coding buddy

Learning these tools will transform your productivity as a solo creator into a one man army when it comes to building out projects rapidly. Let’s get started.

Open AI Codex

I’ve recently checked out OpenAI Codex since I really enjoy using ChatGPT as my main source of technical answers, troubleshooting, high level planning, and detailed implementation designs. I’ve found for a few years now that OpenAI makes their tools fairly consistent and high quality when it comes to programming implementation, and the release of their CLI interface for Codex inspired me to finally dive into CLI based agentic coding, where before I was using integrated extensions in my visual studio code like Roo Code and Github Copilot. This was a more recent development, and after trying it to port a few projects between languages, I was really shocked how incredible the tool was. I had a NodeJs project that was a proof of concept and experimental, and I ported it to C# and refactored the database layer with it. With all this, I have a new project running on a much cleaner design and I did it all with Codex doing 95% of the work.

As far as the benefits from CLI based agentic coding vs some sort of GUI, I can’t fully explain if there is a major benefit from a technical perspective. However I do find that most 1st party apps the experience is generally better than a 3rd party approach, especially as we are still in the storming phase of agentic coding. OpenAI has integrated Codex tightly with their AI models and I’d imagine there is an efficiency in there from a model and model use perspective. While I do love Roo Code and it’s incredible feature set, it does also seem to chew through tokens a bit inefficiently it seems, and since I use OpenRouter as the provider which means I cost myself a lot of money in token usage. To me, something with tool usage and file system browsing seems to be better in Codex and is also more efficient on token usage, which matters if you start scaling your Codex use since every token is a direct cost to your wallet.

As far as CLI vs Non CLI, the CLI experience is really sublime and saying CLI is a bit disingenuous to what the full experience is. Codex is essentially a full on application just presented in the terminal for you. I find it beautiful and simple in its display and feedback of what it is working on. It’s a real pleasure to use and since it’s terminal based, you don’t have a lock in with VS Code or another IDE’s custom GUI interface, and it’s highly portable and universal, being just a nodejs application. I’ve never felt limited in it being a terminal application ever since using it, since all it really is is a glorified chat session.There’s also some sort of brain switch that happens when coding when you’re going through the command line versus your Visual Studio Code that maybe makes you think better or differently. Hard to explain but it’s the same reason some people work better at a designated work desk versus a random table somewhere. I’ve mentioned in previous articles I feel it’s important to cultivate a location as a productive zone with the corresponding aesthetic, and this is just an extension of that, just in a virtual world rather than physical.

Before we get started, even if you don’t use Codex, there are some general software engineering patterns below that will help any agentic coder (ex: Claude Code), even if you use a different agent to perform the work. A lot of what we discuss is further on is really just the engineering design mindset applied, and that is universal regardless of who or what codes the software.