Stuart Breckenridge
CodeAI

Experiments with the Codex and Claude Agents

Experiments with the Codex and Claude Agents

I’ve been experimenting with agents: Codex on a Python-to-ExpressJS conversion, and Claude in a Swift Package. The results have been impressive.

The remainder of this post was originally for members only.

Codex

Singapore Buses has a back-end server, written in Python with FastAPI, that is used to manage storage of APNS tokens, retrieve bus arrival estimates and push that data out as Live Activity notifications, and storage of aggregated session events for users. I wrote the server application in Python simply to get some experience with the language. I have, however, been wanting to re-write it as an ExpressJS app for quite some time.

Enter Codex.

I downloaded Codex and gave it permission to the project’s directory. I gave it one prompt:

Can you convert this project to ExpressJS?

Codex took less than two minutes to convert public routes, middleware, database, and schedulers, while selecting and replacing third-party Python packages with similar npm packages (e.g., apns2 was replaced with @parse/node-apn).

The results was a working application with one defect—the payload for Live Activities was empty 🫣. Once that was fixed and the rest of the code tested, it was more-or-less a drop in replacement on the server (after changing PM2’s configuration file).

Claude

In Xcode, I enabled Claude’s agent and gave it dominion over my Swift Package LandTransportKit which is what I use in Singapore Buses. The goal of this experiment was to have it write documentation for the package as a Documentation Archive (DocC). This is something I’ve been meaning to do for quite some time, as I wrote when I published the package in July 2025:

I used the ChatGPT integration to write the documentation for most of struct , class, and func definitions. It hasn’t been used for the code itself, the test cases, or DocC.

The prompt:

Write documentation for this package in the documentation archive.

The results speak for themselves. Not only is the package extensively documented, there’s also example usage in UIKit and SwiftUI, along with prebuilt SwiftUI Views.

These experiments have left me impressed with what the Codex and Claude agents are capable of. Both were fast, understood the prompts, and, ultimately, I got the results I wanted.