Making Code Changes with Codex

Now that you know what Codex is and how it fits into your workflow, let’s focus on the basics of making code changes using natural language prompts. This lesson will guide you through the process step by step, with clear formatting and practical advice.

Codex is powered by a specialized AI model that reads your instructions in plain English and analyzes your codebase to generate suggestions. When you type a prompt, Codex scans the relevant files, understands the structure and logic of your code, and proposes a change. You always see a preview before anything is applied, so you remain in control.

Codex can work with a wide range of programming languages and file types. It’s designed to help with everyday development tasks, from small edits to more involved refactoring. However, its effectiveness depends on the clarity of your instructions and the complexity of the task.

Codex is a powerful assistant, but it has its strengths and limitations.

What Codex Can Do:

• Make code changes based on your natural language instructions (add, remove, rename, refactor, etc.)
• Update code across multiple files if your prompt is clear
• Help automate repetitive or tedious edits
• Suggest improvements or modernizations to your code
• Show you a preview of every change before you approve it

What Codex Cannot Do:

• Make changes without your explicit approval
• Understand highly ambiguous or incomplete prompts
• Replace deep code reviews or complex architectural decisions
• Run or test your code automatically
• Guarantee perfect results for very complex or project-specific tasks

For best results, use Codex for well-defined, actionable changes and always review its suggestions.

The quality of your prompt directly affects the quality of Codex’s suggestions. Here are some practical examples to help you get started:

Suppose you want to add a print statement to the beginning of a file. You could type:

Add a print statement that says "Hello from Codex" at the start of main.py

This is a very basic example. In real projects, you’ll often want to use Codex for tasks that are more repetitive or tedious to do by hand.

For instance, if you need to rename a function throughout a file, you might write:

Rename the function fetch_data to load_data in data_utils.py

Codex will find the function definition and update all references in the specified file. This is a common task that can be error-prone if done manually, especially in larger files.

Or, if you want to clean up your code before sharing it, you could ask:

Remove all print statements from utils.py

Codex will scan the file and suggest removing every print statement, saving you time and reducing the chance of missing one.

After you enter your prompt, Codex will show you a preview of the proposed changes. You can approve the change if it looks correct, ask for an explanation, edit the suggestion, or decline it. Always review the preview carefully, especially as you start using Codex. This helps you build trust in the tool and ensures your code stays safe.