Quick Answer
OpenAI Codex can help beginners build Android apps with Expo and TypeScript using simple prompts. You can generate the app, preview it on your phone with Expo Go, fix errors, build an APK with EAS, and even add optional cloud sync using Supabase.
We recently shared a detailed guide on how to build Android apps using Google Antigravity. That approach is best for someone who wants an affordable way to build AI apps that work.
Current Google models in Antigravity offer way better rate limits than models from ChatGPT or Claude. However, Gemini isn’t the best for building advanced AI apps or if you want to include any other advanced features in your app.
For advanced apps, using Claude or <a href="https://techpp.app/update-tracker/openai-codex-changelog” rel=”nofollow noopener” target=”_blank”>ChatGPT Codex is the most reliable option. In this guide, you will learn how to build Android apps using Codex. OpenAI’s ChatGPT models in Codex are not free; you need a minimum ChatGPT Plus subscription to access top models. Also, the rate limits are very poor, which you can easily exhaust if you play with them for some time.
However, these models are way more powerful and currently among the leading frontier models. Also, thanks to the different connections, plugins, and MCP servers, the process of building Android apps using Codex is more convenient and takes fewer steps compared to Google Antigravity. In this guide, you will learn how to build Android apps using OpenAI Codex.
Prerequisites
To build an Android app in Codex, you need:
- ChatGPT Plus or Pro subscription (which you can get from here)
- An Android app with Expo Go installed – Download the Expo Go app
- An Android phone
- A free account on supabase.com –Sign up here
- A free account on expo.dev
Once done, you can follow the process below to build Android apps using OpenAI Codex.
Set Up Codex
Step 1: First, download and install the ChatGPT app on your Mac or Windows. It is also available for Linux.
Step 2: Once installed, sign up with your ChatGPT Plus or Pro subscription account.
Step 3: Once done, switch to Codex.
Step 4: Now tap on New chat, and from here, tap on Choose Folder.
Step 5: Now, you can create a new folder or use the existing folder, which stores all your app files.
Create Your App
Step 1: Now, enter the following prompt. You can edit the prompt to include your own prompt. For this guide, I am building a simple Pomodoro app.
Build a simple Pomodoro timer app using Expo and TypeScript.
The app should let users start, pause, resume, reset, and skip Pomodoro sessions. Include focus, short break, and long break modes. Show the remaining time clearly, track completed focus sessions, and save the timer settings and session history locally using SQLite.
Create a clean, polished mobile UI that works well on Android. Do not create an Android build yet. First, implement the app, check for errors, and explain how I can preview it using Expo Go.
Step 2: Now, in the model selector, select GPT-5.6 Sol or GPT-6 Astra.
In this guide, we are building a simple Pomodoro timer application that keeps track of your focus and how much time you have been distracted.
The latest Codex GPT-6 Astra model is very good at frontend development. Even if you haven’t included reference images of the app UI, since it is a simple app, it can generate a very reliable UI based on the prompt.
However, if you want something unique that is personalized to yourself, I highly recommend submitting UI references. It will generate exactly what you are looking for, including the font options that you used while designing the app. You can use Google Stitch to generate UI.
Design the UI With Google Stitch (Optional)
You can use Google Stitch for designing the UI. It is very similar to Figma, but more AI-focused: it lets you generate UI through AI prompts and also lets you customize with basic tools.
We created a detailed course on how you can create UI designs using Google Stitch, with 12+ videos guiding you through all the core features of Google Stitch.
If you want to quickly create UI designs using Google Stitch, you can go to stitch.withgoogle.com and follow these steps:
Step 1: Paste your prompt (for whatever your app is) into the prompt area.
Step 2: Wait for Google Stitch to generate your UI designs.
Step 3: Tap on the prototype icon at the top to check the preview.
Step 4: Export and save it as a zip file.
Step 5: To upload the references to the Codex file in the entry box, after entering the prompt, you can click on the plus icon and select Files and folders. From here, you can attach the UI reference images (Remember you need to extract the folder).
You can attach up to 10 images, which is more than enough for a basic or even a medium-level app with all those screens.
Preview the App on Your Phone
Step 1: Wait for Codex to generate the full design in the Expo app, and then you can enter the prompt so that it can show you a preview of the app. You can install the Expo Go app on your Android phone. Open the app and scan the QR code generated by Codex after following these steps.
Step 2: Carefully review everything and ensure that everything works.
Step 3: Once finished, enter this prompt to preview the app on your mobile. If it asks you to run the terminal code, you can ask GPT to run the code for you.
Start the Expo development server for this project and show me the QR code so I can open the app in Expo Go on my Android phone. Check the app for errors first. Do not create an Android build yet. Run every command and give me the final QR code to scan.
GPT models are often known for lying: even though something isn’t finished, it confidently mentions that it has finished or fixed the issue. I highly recommend you verify each and every output.
Build the Android App
Once everything is ready, you can build the Android app. Since we are using Expo, the free version only allows you a limited number of builds, and afterward, you need to wait for a set time to build it into an Android app.
Step 1: Once everything is ready, enter the following prompt:
Prepare this Expo project for an Android build using EAS Build. First, inspect the project and create or update the required eas.json configuration for a preview Android APK.
Step 2: Now, once you have created your Expo account (if you haven’t, you can go to expo.dev and create one), open the terminal in this app folder and run the following command:
Step 3: Now sign in to your account using your username and password. This is a one-time process. Every time you want to build an Android app, you can just ask Codex to use this account to build it.
Step 4: Once that is created, go back to the Codex app and enter the following prompt:
Configure EAS Build for this Expo project and create a preview Android APK. Use the Expo account currently signed in on this computer. Check the configuration and fix any project errors before starting the build. When the build finishes, give me the download link and explain how to install it on my Android phone.
Step 5: Once you have entered the prompt, Expo.dev will begin creating your app. You can see the progress from your account, or you can directly click on the link provided by your Codex platform. Once it’s done, you can see the status.
Remember that the Expo free version only offers limited builds in fast mode. Once your limits are reached, you need to stay in the queue, which can take around 3 to 4 hours, or even 7 hours, depending on the line, to build your Android app.
Step 6: And once it’s done, Expo provides a downloadable link that you can copy and directly share with your Android phone.
Step 7: On your Android phone, you can install the app. Remember that Google Chrome (or whatever browser you are using) won’t allow you to install apps from third-party or unknown sources by default; you will need to grant the browser permission to install them. Once permitted, you can install the app using the package installer on your device.
Add Cloud Sync With Supabase
You can follow a similar process if you want cloud sync. To access your app data on other devices, you need to upload it to the cloud. To do that, you can use a free Supabase database and connect your app to the Supabase backend so it can store your data. Supabase offers three projects for free.
Here is how to connect your app to Supabase. This is completely optional and only recommended if you want your app data to be cloud-synced and need to use the app on other devices. Otherwise, the current app you built uses local SQLite, which stays on your device unless you delete it.
For Supabase, you can directly install the Supabase extension or use an MCP server. To do that:
Step 1: Create a free account on Supabase.
Step 2: Create a new project.
Step 3: Copy the project URL ID and the shareable URL. You can watch the video below.
Step 4: Go back to Codex and enter the following prompt with your details:
Connect the official Supabase MCP server to my existing Supabase project.
Project reference: YOUR_PROJECT_REFERENCE
Scope the connection to only this project and begin in read-only mode. Open the browser authentication flow so I can sign in and approve access myself. Do not access any other project and do not make any database changes yet.
Step 5: Now, to connect your Supabase, go back to Codex and enter the following prompt:
Add optional cloud sync to this Expo Pomodoro app using my connected Supabase project.
Keep the existing local SQLite functionality as an offline fallback. Create a reviewed database migration for user profiles, timer settings, and completed focus sessions. Enable Row Level Security and ensure each user can only access their own data.
Use only the Supabase project URL and publishable key in the Expo app. Never use or expose a service role key in the mobile app. Show me the migration and security policy plan before applying any database changes.
Don’t worry. Even if the MCP isn’t working, Codex has computer use. It can browse the web for you, create an account, create a Supabase project, and do much more.
Step 6: Once the app is generated again, you can ask Codex to start building in expo.dev. Copy the URL on your smartphone and download the app.
Step 7: This time, when you are installing it, you will see an “Update” option instead of “Install” since you have already installed the app. Now you are updating it to the new version.
Final Thoughts
This is how you can easily create Android apps using Expo with Codex. Your app is just one idea away, or perhaps even one Codex subscription away, and you can get any app you want. It could be a video editing app, or the app you have wanted all the time but no developer has built yet.
Remember that everything is in your control, so you don’t need to worry about any feature. You can add as many features as possible. If you have any issues while creating the app, you can comment below. I am ready to help you.
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#AI#android#android app#Codex#Developer#how to guide#openai
