This content originally appeared on DEV Community and was authored by Rajni Devi
From a Solo Dev Who Actually Did It
Hey, I’m Rajni — an AI developer who once spent 72 hours straight trying to get a language model to write a love poem in Hindi. It failed. But that failure taught me more than any tutorial ever could.
Today, I’m walking you through how I built a working ChatGPT-like AI — not with billion-dollar GPUs, but with free tools, open-source models, and a lot of coffee.
This isn’t theory. This is code that runs today.
Step 1: Pick Your Brain (The Model)
You don’t need GPT-4. Start with open-source LLMs that fit on a laptop.
# Best free models (2025)
- microsoft/DialoGPT-medium → Fast, conversational
- google/flan-t5-large → Great for reasoning
- meta-llama/Llama-3-8B-Instruct → Best quality (needs 16GB VRAM)
I chose DialoGPT-medium — it’s lightweight, MIT-licensed, and perfect for chat.
from transformers import AutoTokenizer, AutoModelForCausalLM
model_name = "microsoft/DialoGPT-medium"
tokenizer = AutoTokenizer.from_pretrained(model_name)
model = AutoModelForCausalLM.from_pretrained(model_name)
Step 2: Make It Talk (The Chat Loop)
Here’s the core chat engine — 20 lines that power the whole thing:
def chat_with_bot(user_input, chat_history_ids=None):
# Encode user input
new_input_ids = tokenizer.encode(user_input + tokenizer.eos_token, return_tensors='pt')
# Append to history
bot_input_ids = torch.cat([chat_history_ids, new_input_ids], dim=-1) if chat_history_ids is not None else new_input_ids
# Generate response
chat_history_ids = model.generate(
bot_input_ids,
max_length=1000,
num_beams=5,
early_stopping=True,
pad_token_id=tokenizer.eos_token_id
)
# Decode reply
reply = tokenizer.decode(chat_history_ids[:, bot_input_ids.shape[-1]:][0], skip_special_tokens=True)
return reply, chat_history_ids
Human Touch: I added a
personality_prompt— “You are a sarcastic AI poet from Mumbai.” The bot now replies in shayari when bored.
Step 3: Wrap It in a Web App (FastAPI + Streamlit)
No one wants a terminal bot. I built a beautiful UI in 30 minutes.
# app.py (Streamlit)
import streamlit as st
from chat_engine import chat_with_bot
st.title("RajniGPT — Your Desi AI Friend")
if "history" not in st.session_state:
st.session_state.history = None
user_input = st.text_input("You:")
if user_input:
reply, st.session_state.history = chat_with_bot(user_input, st.session_state.history)
st.write(f"**Bot:** {reply}")
Run:
streamlit run app.py
Step 4: Deploy for Free (Docker + GitHub Pages)
# Dockerfile
FROM python:3.10-slim
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
CMD ["streamlit", "run", "app.py", "--server.port=8501"]
Push to GitHub → GitHub Actions → Deploy to Railway.app (free tier).
Step 5: Make It Smarter (Fine-Tuning)
Want it to sound like you? Fine-tune on your WhatsApp chats.
from transformers import Trainer, TrainingArguments
# Load your chat logs
dataset = load_dataset("text", data_files="my_chats.txt")
training_args = TrainingArguments(
output_dir="./rajni-gpt",
num_train_epochs=3,
per_device_train_batch_size=4,
save_steps=500,
)
trainer = Trainer(model=model, args=training_args, train_dataset=dataset["train"])
trainer.train()
Pro Tip: Use LoRA (Low-Rank Adaptation) — fine-tune in 2 hours on a $10 Colab GPU.
What I Learned (The Human Part)
- Week 1: Model hallucinated. It said “Namaste” to a pizza order.
- Week 3: Added memory. Now it remembers your dog’s name.
- Week 6: Users asked it for life advice. One cried. I cried.
This isn’t just code. It’s connection.
Your Turn
- Fork the repo → github.com/rajni-ai/chatgpt-clone
-
Run
setup.sh→ 2 minutes - Change the personality → Make it a chef, a therapist, a stand-up comic
- Deploy → Share with friends
Want to Build the Next ChatGPT?
Comment below with:
- Your GitHub
- What you want the AI to do (roast code? write songs?)
I’ll personally review your PR and help you ship.
Let’s build AI that feels human.
Rajni
Solo Dev | 2M+ AI Interactions | Building in Public
This content originally appeared on DEV Community and was authored by Rajni Devi
Rajni Devi | Sciencx (2025-11-01T13:51:22+00:00) Build Your Own AI Chatbot Like ChatGPT — A Practical Guide with Code. Retrieved from https://www.scien.cx/2025/11/01/build-your-own-ai-chatbot-like-chatgpt-a-practical-guide-with-code/
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