How to Build AI Applications with ChatGPT API: Complete Developer Guide 2025

Getting Started with ChatGPT API

OpenAI's ChatGPT API allows developers to integrate powerful AI capabilities into their applications. Let's build something amazing.

Setting Up

First, install the OpenAI SDK:

npm install openai

Basic API Call

import OpenAI from 'openai';

const openai = new OpenAI({
  apiKey: process.env.OPENAI_API_KEY,
});

async function chat(message: string) {
  const response = await openai.chat.completions.create({
    model: 'gpt-4',
    messages: [
      { role: 'system', content: 'You are a helpful assistant.' },
      { role: 'user', content: message }
    ],
  });
  
  return response.choices[0].message.content;
}

Building a Chatbot

Create a conversational AI with message history:

const conversationHistory = [];

async function chatWithHistory(userMessage: string) {
  conversationHistory.push({ role: 'user', content: userMessage });
  
  const response = await openai.chat.completions.create({
    model: 'gpt-4',
    messages: conversationHistory,
  });
  
  const assistantMessage = response.choices[0].message;
  conversationHistory.push(assistantMessage);
  
  return assistantMessage.content;
}

Key Takeaways

1. ChatGPT API is straightforward to integrate
2. Maintain conversation history for context-aware responses
3. Use system prompts to customize AI behavior