Quick start

This guide will teach you how to add Inngest to a FastAPI app and run an Inngest function.

💡 Inngest currently supports FastAPI, Flask, and Tornado. If you'd like support for your favorite framework please open an issue on GitHub!

Create an app

Use Python 3.10 or higher.

Create and source virtual environment:

python -m venv .venv && source .venv/bin/activate

Install dependencies:

pip install fastapi inngest uvicorn

Create a FastAPI app file:


from fastapi import FastAPI

app = FastAPI()

Add Inngest

Let's add Inngest to the app! We'll do a few things

  1. Create an Inngest client, which is used to send events to an Inngest server.
  2. Create an Inngest function, which receives events.
  3. Serve the Inngest endpoint on the FastAPI app.


from fastapi import FastAPI
import inngest
import inngest.fast_api

# Create an Inngest client
inngest_client = inngest.Inngest(

# Create an Inngest function
    # Event that triggers this function
async def my_function(ctx: inngest.Context, step: inngest.Step) -> str:
    return "done"

app = FastAPI()

# Serve the Inngest endpoint
inngest.fast_api.serve(app, inngest_client, [my_function])

Start your app:

uvicorn main:app --reload

Run Inngest Dev Server

Inngest functions are run using an Inngest server. The Inngest Dev Server is the standard way to locally run an Inngest server:

npx inngest-cli@latest dev

After a few seconds, your app and function should now appear in the Dev Server UI:

💡 You can register multiple apps and multiple functions within each app.

Run your function

Click the function's "Trigger" button and a run should appear in the Dev Server stream tab: