ChatGPT & Claude (MCP)
How to Connect Apps to ChatGPT with MCP or an API
ChatGPT can talk to the software you use, but only some apps are already in its Plugins list. For everything else there are two routes, and which one you take depends on what the app offers. If the app has an MCP server, press Add on the Plugins page and pick Create MCP App, not Create plugin or Upload plugin archive: those two build plugins that only work in the ChatGPT desktop app, not on the web or your phone. Name it, paste the app's MCP URL, and if you don't know which authentication option it uses, try OAuth first and work down the list. MCP stands for model context protocol, the standard way one application talks to an AI assistant, and you can usually find an app's MCP URL on a Developers or For agents page, or by searching the app's name plus "MCP". If there's no MCP, search the app's name plus "API" and check its endpoints do what you need, then get an API key from the app's settings. ChatGPT's Create plugin option can turn that API into a plugin, but it was janky in testing and only works on desktop. To use the app everywhere, save the key in Carly under Connect an API, add the Carly plugin in ChatGPT, and ask Carly to use the key you saved.
Step by step
- 01
Search ChatGPT's Plugins list first
Click Plugins on the left. A lot of apps are already there, so search for yours before doing anything else. If it's listed, add it and log in.
- 02
Press Add and choose Create MCP App
If your app isn't listed, press Add in the top right. Skip Create plugin and Upload plugin archive: plugins made that way only work in the ChatGPT desktop app, not on the website or your phone. Pick the third option, Create MCP App. If it isn't in the menu, turn on Developer mode under Settings, then Security and login.
- 03
Find the app's MCP URL
On the app's website, look for a Developers or For agents page, which is where the MCP URL usually lives. If you can't find one, search Google for the app's name plus "MCP". MCP stands for model context protocol, a standard way for one application to talk to an AI assistant.
- 04
Name it, paste the URL and pick authentication
Give the app a name, paste the MCP URL, and choose an authentication option. You don't need to know which one is right: try OAuth first, and if it doesn't work, try the next one. Agree to the warning and press Create.
- 05
No MCP? Check the app's API
Search the app's name plus "API" and open its API reference. Skim the endpoints, which list what the app lets you do, and make sure the one you care about is there, such as creating an event.
- 06
Get an API key
Log in to the app and look in its settings for an option to create an API key. Every app keeps it somewhere different. If you can't find it, email the app's support and ask where it is.
- 07
Know the catch with Create plugin
Back under Add, Create plugin walks you through turning an API into a plugin. In the video it was a little janky and didn't always work, and the plugin it makes only runs in the ChatGPT desktop app.
- 08
Save the key in Carly to use it on the web and your phone
Create a Carly account, open Integrations and go to Connect an API. Paste the API key there. If the other fields look confusing, store the key only and the agent will work out how to use it.
- 09
Add the Carly plugin and ask for the app
In ChatGPT, open Plugins, search for Carly and add it. Carly is listed in ChatGPT's plugin directory, so there's nothing to build. Then ask Carly to use the API key you saved, for example to create an event at 8 PM. It works in ChatGPT or Claude, on the web and on your phone.
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