How to Make a ChatGPT Plugin With Python and FastAPI

ChatGPT plugins provide a new medium for developers to take advantage of OpenAI’s powerful GPT-4 model. plugins give ChatGPT access to tools via a REST API. When a plugin is installed in a user’s ChatGPT session, the model may decide to use the plugin as a part of it’s response.

You can develop plugins that enable ChatGPT to plan travel, go shopping, or do complex mathematics. In this tutorial, you’ll learn the basics of developing a ChatGPT plugin using Python and FastAPI.

This tutorial assumes you have Python and Poetry installed. For information about how to create a plugin in other languages, see:

If you want to follow a video tutorial, you can watch the video version of this tutorial below:

Step 1: Set up the Python project

Create a new Python project with poetry by running:

poetry new python-chatgpt-plugin

This will create a project with the following directory structure:

python-chatgpt-plugin
├── pyproject.toml
├── README.md
├── python_chatgpt_plugin
│   └── __init__.py
└── tests
    └── __init__.py

Next, install FastAPI and uvicorn using Poetry:

poetry add fastapi uvicorn[standard]

Note: If you are on a Mac you’ll need to wrap uvicorn[standard] in quotations: "uvicorn[standard]"

Finally, activate the virtual environment by running:

poetry shell

Step 2: Create the plugin API

ChatGPT interacts with plugins via a defined REST API. You can quickly create a REST API in Python using FastAPI. First, create a new file in the python_chatgpt_plugin folder called main.py. Then, add the following code to the file:

from fastapi import FastAPI

app = FastAPI(
	title="Python ChatGPT plugin",
	description="A Python ChatGPT plugin"
)

@app.get("/hello", description="Says hello from the ChatGPT plugin")
async def hello():
  return {"message": "Hello from the plugin!"}

This code creates a new FastAPI application and adds a single GET route at the path /hello. The /hello route will return a JSON object with the given message from the plugin. Notice the description argument in the route describes the action the given route will take when called. It’s important to make these descriptive, as it provides context to the model to decide what action to take when using your plugin.

Step 3: Set up CORS middleware for development

In order to test your plugin locally before deploying to production, you need to configure your application to allow Cross-Origin Resource Sharing (CORS) from the ChatGPT website. CORS enables ChatGPT to request access to resources from your locally running webserver. To setup CORS with FastAPI, you can use the CORSMiddleware:

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

app = FastAPI(
	title="Python ChatGPT plugin",
	description="A Python ChatGPT plugin"
)

# Enable CORS for https://chat.openai.com/
app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://chat.openai.com"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

@app.get("/hello", description="Says hello from the ChatGPT plugin")
async def hello():
  return {"message": "Hello from the plugin!"}

CORSMiddleware will configure CORS for your application from https://chat.openai.com.

Step 4: Create the plugin manifest

Every ChatGPT plugin must ship with a plugin manifest hosted on the same domain as the API. ChatGPT looks for the plugin specifically at the path /.well-known/ai-plugin.json. You can read more about the specifics of the plugin manifest in our What is the ChatGPT plugin manifest? post.

For your plugin, start by creating a new file in your plugin directory called ai-plugin.json. Next, add the following:

{
  "schema_version": "v1",
  "name_for_human": "My First plugin",
  "name_for_model": "pythonPlugin",
  "description_for_human": "My first ChatGPT plugin",
  "description_for_model": "plugin which says hello.",
  "auth": {
    "type": "none"
  },
  "api": {
    "type": "openapi",
    "url": "http://localhost:8000/openapi.json",
    "is_user_authenticated": false
  },
  "logo_url": "http://localhost:8000/logo.png",
  "contact_email": "support@example.com",
  "legal_info_url": "http://www.example.com/legal"
}

In this example, the “auth” field is set to “none” because this plugin doesn’t require authentication. However, depending on your use case, you might need your plugin to handle authentication. For more information about how to implement authentication in a ChatGPT plugin, you can refer to our ChatGPT Plugin Authentication Guide.

Next, add a route for accessing the plugin manifest from your app:

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
import json

app = FastAPI(
	title="Python ChatGPT plugin",
	description="A Python ChatGPT plugin"
)

# Enable CORS for https://chat.openai.com/
app.add_middleware(
    CORSMiddleware,
    allow_origins=["https://chat.openai.com"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# Load and serve the plugin manifest
with open('ai-plugin.json', 'r') as manifest_file:
    manifest_content = json.load(manifest_file)

@app.get("/.well-known/ai-plugin.json")
async def serve_manifest():
    return manifest_content

@app.get("/hello", description="Says hello from the ChatGPT plugin")
async def hello():
  return {"message": "Hello from the plugin!"}

And that’s all you need!

Step 5: Install and test your plugin

First, start your plugin server locally by running:

uvicorn python_chatgpt_plugin.main:app

You can verify it worked by navigating to http://localhost:8000/docs in your browser:

SwaggerUI documentation for your plugin

Next, navigate to the ChatGPT UI and select the plugin model:

Selecting the plugin model

Then, you’ll want to select the plugins dropdown, navigate to the plugin store, and click “Develop your own plugin” in the bottom right:

Selecting develop your own plugin

Finally, type your localhost URL into the plugin form:

Typing the address of your plugin

After awhile, you’ll see the following:

Successfully adding your plugin

Click “Install localhost plugin” to continue. With your plugin enabled, you can start to interact with it using ChatGPT. For example, try typing in “Say hello from my plugin” into the chat window:

Successfully using the plugin

Congratulations! You’ve successfully made your first ChatGPT plugin with Python and confirmed it works locally. Next, check out our deployment and hosting guide to learn about deploying your plugin to production.