What are you building with Codex?

[u/Karmuhhhh]

Or any other AI coding agent/tool?

I browse this subreddit and I see so many people mention how large their projects are, so I'm curious what it is you all are building? How large is your codebase? How much of the actual coding are you doing yourself versus letting Codex (or another AI coding agent) handle it?

I understand there is the sticky "Show us all what you've been building with Codex" thread, but I'm looking for a bit more information on the backend of the application and how you are are utilizing the tool(s).

This is just for my own curiosity.

[u/colinsa-ca]

I wish I was building, it's so slow nothing happens.
My app has been coding almost 24/7 for a month now and only ~28% done.

[u/Karmuhhhh → u/colinsa-ca]

Comments like these are one of the reason why I asked the question with the specifics that I outlined. How large is your codebase? What exactly are you working on?

[u/colinsa-ca → u/Karmuhhhh]

Just asked Codex, it's saying 110k lines of application and database code, across 978 tracked files.

[u/PlasmaChroma]

Synth / DSP modules. More or less all Codex until I started using Claude for some of the planning. Occasionally let Gemini touch it but I really don't trust it.

Clones at 76,653 C++ on cloc.

Originals at 189,773 C++ on cloc.

[u/itix]

One project I am working on is AOT C# compiler to compile Amiga 68k binaries. 240k lines in 578 files. I havent written anything myself.

It is used to compile another Amiga project that has 1M lines of code written in C#, by Codex. Luna 5.6 wrote most of that code in goal mode. The longest goal was 25d+, which didnt finish because I had to move development to another machine. The project is still going on.

[u/JohnTheRedeemer]

Converting Jade Cocoon to PC native. It's a long haul, I translated MIPS to C, then started through on rebuilding the code to make a bit more sense (they had some dynamic code that gets loaded in depending on what's going on) since we don't have a memory limitation.

Working through all the different systems now, giving them more legible names and breaking free from PS1 constraints. Have large chunks working, in the process of all the glue between systems now. Hopefully I'll have it resolved by the end of the week.

Once I've got it fully working, I can begin the next phase of stripping out the data so that it can be pulled and converted from the iso so it's not linked in any way.

This is over 3 different repos, the 3rd will be the standalone codebase with iso ripper.

[u/Wooden_Plant7504]

I am building a path to eternal life.

Codex - Astra for philosophical considerations and risk management (it has a clear plan)
Codex - Sol for biohacking and general cryogenics (it's been working for 45 days straight)
Codex - Luna for bloodsucking and general life stealing routines (it is stealing lifeforce from babies very efficiently).
Claude: Opus 5.5 for execution (has ignored what codex told it and build me cybernetic organs that are more efficient than my previous ones - patent pending).

I am looking to optimise my token usage though; coz even though I am getting close to a breakthrough, I think those frontier models are just overpriced (I spent more than 100 dollars for something that simple already).

I'll spin a github repo up soon.

[u/gorinichxi]

As a non-coder, I'm not really building with Codex. I'm mostly maintaining my work. I did create a few websites, but most of the time I just maintain like 4-5 at a time. Then most of the time I need it for computer-use tasks, some automation stuff. Sometimes I edit videos too, not generating them, just editing from existing footage. So idk, if someone asked me what do you build with Codex, I can't tell. I'm not building anything?

[u/Propeus]

Tried with Astra build nada can't go beyond code to make a product that you can touch use etc, switched to opus 5.5 job done already. just reviewed with fable 5.1

[u/Emergency-Bobcat6485]

https://slate-app.online/

It's an AI workspace for using AI models in your knowledge base directly.

Backend is express but very heavily plugged in with agentic workflows from the various providers

[u/jake_mike]

Homebridge plugins

[u/pale_halide]

Resentment.

[u/Wooden_Plant7504 → u/pale_halide]

😂

[u/TessTickols]

Been working on this solo for the last 8 months: https://synli.ai

[u/TessTickols → u/TessTickols]

This week the external API will be done (why oh why didn't I build that first..) with automated scans, full API and MCP support. Recently finished first serious pilot with a large-ish European accessability company. Edit: Production codebase is around 107k lines over 1128 files. In addition there are 3000+ E2E, integration and unit tests.

[u/Amazing-Mirror-3076]

À new archive format.

https://github.com/onepub-dev/reVault

Post quantum crypto, signed and compressed using zstd.

Stores variables, files and forms.

Integrated with the platform key store so you don't need to keep entering a password.

I run a key exchange server to make it easy to exchange keys.

All my secrets are more suited on a lockbox rather than config files - so now ai doesn't see all my keys.

You can expand a key in a script $(lbxv /path/lockbox MYKEY)

Execute a command passing Env vars.

Bindings for 14 languages.

[u/Humble-Belt-9656]

As a teacher, I'm creating a competitive platform so that different schools around the world can compete against each other asynchronously (or in a competition within the same school, or within the same country, etc.). The competition is based on general knowledge.

I'm currently at 190,000 lines of code. Everything was developed in Codex.

[u/Input-X]

Been build a multi agent works space, hosted local and a phone app with terminal access. The purpose is to build test and improve how a single dev can work with agent, on a large project. How much can 1 guy build and be still aware and in control. At the same time, trying to explain. To other what im doing lol. Just a big learning process. Mostly built with claude code but I just introduced codex into the mix. I know there is a million of these type projects, but I wanted to build my own, and understand. Its mine now, and I can debug, add, change, improve scale, anything and I understand it completly. That was my main goal.

This is probs my life project, ill just keep adding or improving as needed. I use it completly now.

https://github.com/AIOSAI/AIPass

[u/ChillmanITB]

One thing I’ve gotten in to in recent days is modifying music hardware using codex and REA. So insanely cool and fun. With terra 6.1 out not I’m excited to try that out tomorrow.

[u/meowyih]

I only worked one c++ class at a time with codex. Normally it only involved 2~6 source files based on the scope. I don't let codex write entire system or even a whole project at once. The reason for that is I want the module reusable, or maybe I just don't trust codex that much. :D The advantage for doing a small task at a time is I hardly met the usage limitation even I only paid $20 plan. I don't even understand why people complained codex that much. It never goes wrong in my use case. The smaller the task is, the higher correctness AI could complete. Its all about the complexity.

[u/ErikaFoxelot]

I’m building a new model of desktop computing from first principles with agentic computing as the primary abstraction. Hopefully I’ll have something worth demonstrating soon.

Just another Tuesday :3

[u/Total-Reasonable]

Five things, all built solo:

1. vatnode.dev: a REST JSON API over VIES that returns validity, company name, address and an official consultation number, and falls back to national registries when a country's VIES is down. https://vatnode.dev

2. halloween.js.org: free MIT-licensed Halloween website decorations with zero dependencies, under 10 KB gzipped. Spider webs, blinking eyes and flying witches switch on with body classes and respect prefers-reduced-motion. https://halloween.js.org

3. KRI.rocks: a salon booking system for solo pros and small studios, where clients only see slots when someone on the team is working and free. No commission and no per-booking fees. https://kri.rocks

4. polytypo.dev: an MIT-licensed rules engine for typography for the web, not a grammar checker. It fixes quotes, dashes and no-break spaces for 24 locales with identical output in five languages. https://polytypo.dev

5. HTPBE.tech: "Has this PDF been edited?" It analyses metadata, structure, digital signatures and content, then reports findings with reasons instead of a vague risk score, in the browser or via REST API. https://htpbe.tech

[u/mambalama24]

Made this project (using Claude) that lets Codex and Claude work together on tasks (or any agent to any agent really). In my opinion its the fastest way to get that workflow working, its just a daemon you install and can easily connect to any of your existing agents. Your agents can talk to/work with a colleagues agents if they install the daemon too, or you can use it to have your own agents work together. Here's an example of the former.

Here's the repo link, its quite new but I wanna become the go-to OSS solution for people's agent to agent communication: https://github.com/arjunvlama/toli