Codex: The AI That Codes
Codex was released on 16 May 2025 for Chatgpt Pro, Enterprise and Team users.
Codex by OpenAI is redefining how we think about code. It interprets human instructions and turns them into functioning software across many programming languages. This post dives into how Codex works, its real-world applications, and what it means for the future of development.
What is Codex?
Codex is a fine-tuned version of GPT-3 trained on vast repositories of code and natural language. It’s capable of understanding instructions in plain English and generating accurate code in response.
Sample Prompt:
"Create a FastAPI endpoint that receives a list of integers and returns them sorted."
Sample Output:
from fastapi import FastAPI
from pydantic import BaseModel
app = FastAPI()
class NumberList(BaseModel):
values: list[int]
@app.post("/sort")
def sort_numbers(data: NumberList):
return {"sorted": sorted(data.values)}
How Developers Use Codex
- Rapid prototyping: From CLI tools to full-stack apps.
- Porting code between languages.
- Autogenerating docstrings, tests, and README content.
- Explaining legacy code in plain English.
Live Demo (Conceptual)
Ask Codex: “Write a Python script that reads a CSV and prints the average age.”
import csv
with open('data.csv') as f:
reader = csv.DictReader(f)
ages = [int(row['age']) for row in reader]
print("Average age:", sum(ages) / len(ages))Prompt Engineering Tips
- Zero-shot: Direct, plain-English command
- Few-shot: Include examples before your request
- Chain-of-thought: Break down the steps
Behind the Scenes
Codex is now part of GPT-4, especially in the Chat Completions API. It benefits from larger context windows (up to 128k tokens), function calling, and deeper reasoning capabilities. It is what powers GitHub Copilot and several no-code/low-code platforms today.
Ethical and Security Considerations
- Always validate and test AI-generated code.
- Be aware of hallucinated APIs or insecure patterns.
- Maintain human oversight for critical systems.
The Future of Software Development
Codex is a stepping stone toward autonomous agents that can architect, write, and test full applications. In this new age, developers will focus more on defining what should be built rather than how to write it.
Curious to try it? Start with OpenAI’s Playground or explore GitHub Copilot today.