With the recent release of ChatGPT apps, especially the ChatGPT Apps SDK, developers can now build apps that run directly inside ChatGPT. 🤯
Currently, by default, OpenAI supports just the following apps: Booking.com, Canva, Coursera, Expedia, Figma, Spotify, and Zillow.
In the coming days, they plan to support developer-submitted apps by opening submissions later this year. This is a big moment for everyone who uses ChatGPT, especially developers who can build their own apps, and for the over 800 million ChatGPT users who get to try them.
So, you must know how to build your own apps with the ChatGPT Apps SDK. How cool would it be to create an app that supports over 500 apps and isn't limited to the default OpenAI-supported apps?
That's precisely what we'll cover, from understanding the SDK and running the project locally to temporarily hosting it on Ngrok to access it in ChatGPT.
So, without further ado, let's dive right in.
TL;DR
To quickly summarize what we'll cover in this blog post, here's what we'll go through:
What are ChatGPT apps and the Apps SDK?
Installing Ngrok to host your localhost project on the internet with one command.
How to use Rube to access OpenAI ChatGPT Apps.
How to implement widgets in Next.js with ChatGPT Apps SDK + Rube MCP.
If you work with Next.js and want to learn how to build custom widgets for your ChatGPT Apps, this is the right place to start.
What is ChatGPT Apps and the Apps SDK
ChatGPT Apps are third-party tools that you can run directly in your ChatGPT conversations. The best way to understand this is to think of it as a way to use these apps like Figma, Canva, Zillow, Spotify, and more, and do all sorts of work directly in them without ever leaving ChatGPT.
To give you a better overview, these are some things you can do with ChatGPT Apps:
Say "Spotify, create me a playlist for my study session," and it'll build you a nice playlist in Spotify and play it directly in your chat.
Say "Canva, create me a thumbnail for my blog post with this text," and it'll build you a nice thumbnail for your blog post.
You're seeing where this is headed. This is OpenAI's third attempt to make ChatGPT not just a chatbot, but an all-in-one platform with all apps directly available in it, so you never have to leave ChatGPT.
The first two were custom GPTs, but they didn't work well with the users. However, this is a powerful, more flexible approach that, if adopted, could mean ChatGPT becomes your all-in-one platform.
Well, then what's ChatGPT Apps SDK?
As the name suggests, it's pretty obvious; it's used to build apps that run inside ChatGPT. 🫠
To add more context, it's an open-source toolkit from OpenAI built on top of MCP that lets developers create apps that run directly in ChatGPT.
At a high level, this is how it works:
Your app (e.g., Canva, Figma, etc.) runs as an MCP server that exposes its tools and input/output schemas directly to ChatGPT.
Now, ChatGPT can invoke those tools and, optionally, render the UI components you provide in a sandbox.
Building a ChatGPT App in Next.js with Widgets
The source code mainly consists of basic React code, so I won't explain it from scratch here. It's a GPT app designed to display Google Calendar meeting details with widget support.
This should be a good starting point for you. Feel free to build something similar for your use case with any apps you prefer.
Begin by cloning the project repository using the command below:
Once your environment variables are configured, install the project dependencies:
pnpm install
After installation is complete, start the project with:
pnpm run dev
By default, the app runs on port 3000. Double-check that it’s running on that port, as you’ll need this information later when setting up Ngrok.
Step-2: Expose Your App with Ngrok
Since ChatGPT isn't running locally on your machine, you can't use localhost:3000 when connecting to the app in ChatGPT.
You can host it on platforms like Vercel, but Ngrok is often faster and more convenient for development.
Ngrok lets you share your local project via a temporary public URL, which is perfect for quick testing without redeploying.
Even if you need to make changes, you won't have to push the changes to your repo to trigger the Vercel deployment. Ngrok can work directly from your local filesystem.
Install Ngrok
Make sure that you have Ngrok installed on your machine.
Head over to ChatGPT settings, then under Additional Settings>Apps and Connectors, make sure Developer mode is turned on. This gives you access to add your own application.
Click Create, and fill in the following details:
MCP Server URL: The public URL you just got from Ngrok. Add /mcp at the end, because that's the endpoint in our code that handles the requests from ChatGPT.
For Name and Description, you can put anything you want (show your creativity!)
Authentication: Select No Authentication, as we'll handle authentication with Composio itself. Our app does not support OAuth by default.
See It in Action
Let's see how all of this adds up. Here's a quick demo to give you an idea of our application.
Creating a Google Calendar meeting and viewing the details directly from GPT with widgets? That's really cool.
Advanced: How to use Rube MCP with the ChatGPT Apps SDK?
You know what? You don’t need to worry about any of that if you don’t care about visual feedback or fancy widgets in ChatGPT. This is the right place to start.
💡 We only had to code all of that because I wanted to show you how to use Widgets with ChatGPT Apps + Rube MCP inside Next.js.
None of the coding is necessary. The whole point of ChatGPT apps is to give you direct access to your applications right inside ChatGPT, so if you want all your apps ready to go without extra setup, this is perfect.
Honestly, this is precisely what I’d recommend for your daily workflow. It’s simple, smooth, and gives you access to over 500 apps available on Rube. Pretty cool, right?
Here’s all you need to do:
Make sure that you are in Developer Mode as we discussed earlier.
In the same tab, click Create, and fill in the following details:
For Name and Description, you can put anything you want (show your creativity!)
Make sure you set up OAuth authentication, as we'll be using it to access the tools in ChatGPT.
Now, click on Create.
It will now ask for some access; hit Allow.
If everything goes well, your app should be available on ChatGPT. Make sure that you see all six actions appropriately listed, as these are the core actions Rube uses to manage authentication, prepare tool calls, and stuff.
Here's all 6 Rube actions listed:
RUBE_CREATE_PLAN: Creates a complete step-by-step plan for LLMs.
RUBE_MULTI_EXECUTE_TOOL: Fast and parallel tool executor for tools discovered through RUBE_SEARCH_TOOLS.
RUBE_REMOTE_BASH_TOOL: Execute bash commands in a REMOTE sandbox for file operations, data processing, and system tasks.
RUBE_REMOTE_WORKBENCH: Process remote files or script bulk tool executions using Python code in a remote sandbox.
RUBE_SEARCH_TOOLS: Search for tools to execute the user task.
RUBE_MANAGE_CONNECTIONS: Manage connection with Rube.
This is to give you an idea of all the actions Rube will use to perform your tasks.
And... that's it.
Now, simply head over to your chat, use @<APP_NAME>, in my case @Rube MCP Server, and start talking.
As an example, try saying this:
"@<APP_NAME> send an email to my ex at XYZ. Subject: Guess who. Body: Don’t worry, it’s just AI with Rube… or is it?"
(C’mon, try it, you’ll test two connections at once. 😉 Just kidding…)
Wrapping Up
Alright, now you’ve got a clear idea of how the ChatGPT Apps SDK works, how to set up a custom server powered by Rube, host it with Ngrok, and use it right inside ChatGPT or plug in Rube and get going without any coding at all if you don't care about widgets.
In this post, we walked through everything from building your own custom server with Rube and widget support in Next.js to skipping the code entirely if you want to move fast.
Well, that's all for this! I will see you in the next one.
