Build a Full AI-Driven API with FastAPI + OpenAI in 15 Minutes

From Zero to AI-Powered Endpoint — Use FastAPI and OpenAI to Create Smart APIs in Record Time

If you’ve ever wanted to integrate GPT into your Python apps — to generate text, summarize content, or answer questions — but felt overwhelmed by boilerplate code or complex infrastructure, this post is for you. With FastAPI and OpenAI, building AI-driven APIs is no longer a weekend project. It’s a 15-minute task. Let’s build an API that takes user input and returns AI-generated text using OpenAI’s GPT model — all wrapped in a clean, FastAPI-powered interface.

🤖 Why FastAPI + OpenAI?

FastAPI brings:
  • 🚀 Blazing-fast async performance
  • 🧼 Auto-validation with Pydantic
  • 📃 Auto-generated Swagger docs
OpenAI brings:
  • 🧠 State-of-the-art language models
  • 🧩 Easy-to-use Python SDK
Together, they give you intelligent APIs that are both powerful and easy to build.
 

🛠️ What We’ll Build

We’ll create an API that:
  • Accepts a prompt from the user
  • Sends the prompt to OpenAI’s GPT-4 or GPT-3.5
  • Returns the model-generated response
  • All in JSON format via a /generate endpoint

✅ Prerequisites

Make sure you have:

Install dependencies:

bash

pip install fastapi uvicorn openai python-dotenv