Step-by-Step: Building a Virtual ChatGPT Assistant That Talks Like You

Written By Xi Liu

AI avatars and digital assistants are everywhere right now. From talking customer support bots to personalized shopping concierges, having a version of yourself that speaks on your behalf isn’t sci-fi anymore—it’s a real tool that can help creators, consultants, and business owners scale their work.

There are a bunch of platforms out there building AI avatars or video-based concierges. But if you’re looking to create a text-based assistant that sounds and thinks like you, you can actually do it with ChatGPT’s Assistants API in just a few steps.

Here’s how I built mine—and how you can do the same.

First of All: Why Build a Virtual Assistant That Talks Like You?

If you’re running a business or sharing your work online, chances are you’ve considered tools like Freshdesk or hiring a virtual assistant to help with questions. But not every visitor wants technical support. Sometimes, people just want to understand who you are, what you offer, and what you stand for—without needing to book a call or scroll through 10 pages.

A virtual AI concierge can help your page speak for itself. It reflects your tone, your values, and your vibe—so people can get to know you, even when you’re offline.

Now, let’s go step by step to build your AI assistant

Step 1: Set Up Your Assistant on OpenAI

1. Generate your API key

  • Go to platform.openai.com

  • Create an API key and store it somewhere safe (you won’t be able to view it again later)

2. Create your Assistant

  • Go to the Assistants tab

  • Click “Create Assistant”

  • Name it something like: Virtual Me or [Your Name] Assistant

  • Choose GPT-4 Turbo

  • Turn on File Search

3. Organize and Upload Your Sample Files

  • Gather examples of how you write and talk: blog posts, emails, bios, FAQs, messages etc

  • Organize them into clearly named files like:

    • 01_tone_voice.txt

    • 02_bio.txt

4. Write System Instructions

You are a helpful assistant that speaks like [Your Name]—professional but warm, casual yet clear. Use 01_tone_voice.txt to match my writing style, and 02_bio.txt to answer personal background questions. Be friendly, but don’t overshare personal details.

5. Test

Once set, you can go to the Playground to test how your assistant responds.

Step 2: Call the Assistant API with a Simple Backend

If you already have an app or website, you can call the Assistant API directly and skip this step. If not, you can spin up a simple backend using Vercel in under 30 minutes. API reference link: https://platform.openai.com/docs/assistants/overview

Here’s how:

1. Create a Vercel account

Go to vercel.com and sign up. Click “Import Project” and choose “Import manually”.

2. Set up your backend locally

On your local laptop, create a folder for the backend. You can create a folder and navigate to it in the terminal or use the command:

mkdir ai-assistant-backend  #create a folder ‘ai-assistant-backend’

cd ai-assistant-backend  # navigate to a folder ‘ai-assistant-backend’

Then run the following commands:

touch .env  #create a .env file

mkdir api && touch api/chat.js   #create the javascript 

npm init -y  #Initialize a package.json

npm install openai  #Install the OpenAI SDK

Add both your openAI key and assistant id in the .env file:

OPENAI_API_KEY=your_openai_key_here

ASSISTANT_ID=your_assistant_id_here

3. Add the backend code in api/chat.js

Paste the following code to your chat.js:

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

export default async function handler(req, res) {
  if (req.method !== 'POST') {
    return res.status(405).json({ message: 'Only POST requests allowed' });
  }

  const { threadId, userMessage } = req.body;

  try {
    const thread = threadId
      ? { id: threadId }
      : await openai.beta.threads.create();

    await openai.beta.threads.messages.create(thread.id, {
      role: 'user',
      content: userMessage,
    });

    const run = await openai.beta.threads.runs.create(thread.id, {
      assistant_id: process.env.ASSISTANT_ID,
    });

    let runStatus;
    do {
      runStatus = await openai.beta.threads.runs.retrieve(thread.id, run.id);
      await new Promise((r) => setTimeout(r, 1000));
    } while (runStatus.status !== 'completed');

    const messages = await openai.beta.threads.messages.list(thread.id);
    const lastMessage = messages.data.find(msg => msg.role === 'assistant');

    res.status(200).json({
      threadId: thread.id,
      reply: lastMessage?.content?.[0]?.text?.value || 'No reply generated',
    });
  } catch (error) {
    console.error('API error:', error);
    res.status(500).json({ error: error.message });
  }
}

4. Deploy to Vercel

  1. Push your code to GitHub or GitLab

  2. Go back to your Vercel Dashboard

  3. Import your repo and follow the steps

  4. Under Settings → Environment Variables, add both OpenAI API key and Assistant ID

  5. Click ‘Deploy’. You will get a live endpoint link like ‘https://your-project-name.vercel.app/api/chat’

5. Test your assistant

  1. You can test your assistant using:

  • Postman

  • fetch() in your frontend

  • cURL in terminal:

curl -X POST https://your-project.vercel.app/api/chat \
  -H "Content-Type: application/json" \
  -d '{"userMessage": "Hi, what do you do?", "threadId": ""}'

Step 3: Fine-Tune Your Assistant to Actually Sound Like You

Even with great docs, GPT can still hallucinate or give irrelevant responses. In my case, it mistook several writing project proposals as real projects I was working on and hallucinated several misleading pieces of information. So, it’s really important to keep fine-tuning the assistant as more people engage with it.

1. Add structure and guardrails

  • In your system message, set clear boundaries like:

    e.g. “Do not give legal or financial advice. Don’t share personal contact info.”

  • Define tone explicitly

    e.g. “Friendly, but not overly casual. Confident, but not salesy.”

  • Iterate! Test weird edge cases and keep refining the files it pulls from.

2. Files for Uploading:

  • Tone Samples: Emails, posts, newsletters

  • Bio/About Me: Who you are, what you care about

  • Expertise/FAQ Content: Anything people usually ask you

3. Tips of File Organization:

  • Name your files clearly: 01_tone.txt, 02_bio.txt, etc.

  • Merge scattered writing styles into one consistent tone file

  • Remove drafts, sarcasm, or anything off-brand (GPT will use it otherwise!)

How it has been helping?

My assistant is still new, and I’m actively fine-tuning it while exploring how far it can go. But honestly, I’m already amazed by how helpful it is—for both customer support and personal task automation. I’ll keep experimenting with new ways to personalize AI and push its limits—so stay tuned for what’s next.

Xi Liu
Next

Building a Product with AI Only: What I Learned (and Where It Broke)