OpenAI Codex

What is OpenAI Codex?

OpenAI Codex is OpenAI's dedicated AI coding agent. Two million developers use it every week. It writes code, edits existing code, and runs it autonomously, working through problems rather than just suggesting snippets. If you already use ChatGPT and you want to use AI for development work, Codex is the natural next step.

The model is available inside ChatGPT and via the API. It is one of the most capable coding tools available and it is backed by the most widely deployed AI organisation in the world.

The Astral acquisition

In early 2025, OpenAI acquired Astral, the team behind two of the most widely used Python development tools: uv and Ruff. These are not niche products. uv is a Python package manager and environment tool. Ruff is a Python linter. Together they are used by 179 million developers every month.

The acquisition signals something important about where OpenAI is heading. They are building toward a developer platform, not just a chat interface. Codex is the centre of that strategy, and the Astral team brings deep infrastructure expertise to support it.

If you do Python development, this is significant. OpenAI now owns the toolchain that a large proportion of Python developers rely on daily. Expect tighter integration between Codex and these tools over the coming year.

What it's actually good for

Writing code from a description. Describe what you want to build in plain English. Codex writes the implementation. This works well for scripts, functions, API integrations, and small applications.

Debugging. Share an error message and the relevant code. Codex traces the problem and proposes a fix. It can run the code, check the output, and iterate, which is more useful than a static suggestion.

Automation scripts. If you want to automate a repetitive task, manipulate files, call an API, or scrape data, Codex is well suited to writing the script to do it. You describe the task; it handles the code.

Python development specifically. Given the Astral acquisition, Codex is particularly strong for Python work. Expect this advantage to compound as the tools become more integrated.

Working within the OpenAI ecosystem. If you use the OpenAI API for your products, Codex has a natural advantage: it understands the API well, knows the libraries, and can write integrations quickly.

Who should use it

Codex is primarily a tool for developers. It assumes you can read and review the code it produces, catch mistakes, and know when something has gone wrong. It is not a no-code product.

That said, the direction of travel is clear. As these tools mature, the gap between "developer" and "technically curious non-developer" is narrowing. Codex is more accessible than working with raw model APIs, and OpenAI is actively working to make it useful to a wider audience. If you are comfortable with the idea of running a script or editing a configuration file, it is worth exploring.

For business owners who want to build something without writing code, Bolt, Lovable, or Google AI Studio are better starting points.

How to get set up

1. Subscribe to ChatGPT Plus at chatgpt.com (£20/month) or access Codex via the API if you have an OpenAI account.
2. Open ChatGPT and switch to the Codex model from the model selector.
3. Describe what you want to build or fix in plain English. Include any relevant context, error messages, or code snippets.
4. Review what it produces, test it, and iterate.

Time to get started: Under 5 minutes if you have ChatGPT Plus Do you need a credit card? Yes, ChatGPT Plus is £20/month. API access is usage-based.