Welcome to the first lesson of our course, Vibe Coding with Codex - Build a Full-Stack Next.js Task Manager. In this course, you’ll grow a minimal Next.js App Router project into a fully-featured Task Manager API. Before we write any backend logic, the goal of this unit is much simpler: get comfortable with Codex, learn how to talk to it, and explore your project safely. Think of this lesson as a warm-up that teaches you the habits you’ll rely on throughout the course.

Codex is the built-in AI assistant inside the CodeSignal IDE. It can read files in your project, explain code, create new files, update existing ones, and help you plan your work. Unlike a general chat model, Codex is tightly integrated with the filesystem—meaning it can only interact with files when you explicitly allow it.

Codex works best when you treat it as a junior engineer: reliable, fast, and helpful, but dependent on clear instructions. You stay in control; Codex executes your plan.

Although the CodeSignal environment already includes Codex integration, it’s useful to understand how Codex is typically set up outside this course. This gives you context for how the tool works under the hood and helps you build mental models that apply beyond the playground.

To install and run Codex locally, you would normally perform the following steps:

Then you would configure your API key:

After that, you would start interacting with the Codex CLI:

This opens an interactive session similar to the one you’ll experience inside CodeSignal. You can issue read-only commands, request file edits, and generate new scaffolding. While you won’t run these commands directly in this course environment, understanding the setup helps clarify how Codex integrates with real-world development workflows.

Throughout the course, you’ll use Codex to perform several types of actions:

Read-only exploration
You can ask Codex to summarize what your files do, or explain unfamiliar concepts—without changing anything.

Targeted file edits
Codex can update specific files when instructed. Your prompt must say exactly which file(s) it is allowed to change.

File creation
As the project grows, you’ll ask Codex to create new route handlers, service modules, repository interfaces, and more.

Planning tasks
Codex is also useful for non-code conversations: outlining ideas, describing architectural steps, or drafting a roadmap.

Good prompts are precise and bounded. They explain what to do, where to do it, and what the final result should look like. You’ll practice this style throughout the step-by-step exercises.

Getting the most out of Codex depends on how you communicate with it. Clear, structured prompting leads to predictable results; vague prompts lead to unpredictable or even incorrect changes. Think of Codex as a junior developer: talented, fast, but very dependent on the precision of your instructions.

A good prompt is:

• Specific about which file(s) Codex may inspect or modify
• Clear about whether the request is read-only or editing
• Explicit about what the final output should look like
• Limited in scope so Codex doesn’t infer unwanted changes

A bad prompt is:

• Vague (“fix this,” “make this better”)
• Missing file boundaries (“update the project”)
• Asking for multiple unrelated changes in one request
• Allowing Codex to guess what you want

Below are examples tailored for this project.

1. Read-only file inspection

Read-only request. Summarize the src/app/layout.tsx and explain how RootLayout works. Do not modify anything.

2. Inspect the directory structure:

Read-only request. List all files inside src/app and describe their purpose at a high level.

3. Summarize scripts in package.json:

Read-only request. Display the scripts section of package.json and explain what each script does. Do not change the file.

4. Planning assistance:

Planning request only. Based on the current minimal project, describe what kinds of backend features might be added later. Do not propose code changes or modify files.

Too vague:

How does my project work?

Too broad:

Can you fix everything that looks wrong?

Missing file boundaries:

Update the page so it looks better.

Inviting unwanted edits:

Feel free to modify any files you think are necessary.

These poor prompts cause Codex to guess your intentions, often resulting in unnecessary or incorrect changes. The practices in Unit 1 will help you get comfortable with writing tightly scoped, reliable prompts.

This entire learning path uses a backend-first, Codex-assisted workflow. You will:

• Explore the existing project before writing any logic
• Use Codex to gradually build out new backend folders and files
• Validate Codex’s output and only approve changes you fully understand
• Keep each prompt small and intentional

In this first unit, your main job is observation. You will ask Codex to inspect scripts, display files, and help you understand the minimal setup you’re starting with. Later units will guide you into building API routes, domain types, service functions, and full Task Manager behavior, but none of that begins until you’re comfortable driving Codex correctly.

Before diving into the practices, here is an example of one of the minimal files already in your project. You will inspect this and similar files with Codex shortly.

Root Layout (High-Level Preview)

This file defines the HTML wrapper for all pages:

This component establishes the basic document structure used by every route. It does not contain styling, providers, or navigation—just a clean, minimal shell. In the practice sessions, you will use Codex in read-only mode to explore this file and others in detail, focusing on understanding—not modifying—the starting point.

This lesson is your launchpad. Once you learn how to communicate with Codex effectively, the rest of the project will unfold naturally. The next practices will guide you through safely inspecting your environment and getting comfortable with Codex-driven development.