Your plain-English guide to OpenAI Codex. No coding background needed. Learn what it is, how to download and set it up, how to use projects, and how to build real things from scratch.
It reads, writes, and runs code on your behalf. Think of it as a brilliant assistant who can build apps, fix bugs, automate tasks, and manage your files — all from plain-English instructions.
You do not need to know how to code. You describe what you want, and Codex figures out the how. It runs on OpenAI's GPT 5.4 model and connects to your computer, your GitHub account, and external tools like Slack and Figma.
Official: openai.com/codex · developers.openai.com/codex
Both are AI coding agents but they take different approaches. Here is the honest comparison:
| Feature | OpenAI Codex | Claude Code |
|---|---|---|
| Made by | OpenAI | Anthropic |
| Best for | Background tasks, visual work, git-heavy workflows, parallel coding | Complex reasoning, large codebases, architecture planning |
| Interface | Visual IDE app with sidebar, diff panel, image previews | Terminal-first. Desktop app also available. |
| Models | GPT 5.4, Mini, Spark (Max plan only) | Haiku, Sonnet, Opus |
| Git built-in | Yes. Commit, PR, diff all inside the app | Requires separate tools or VS Code |
| Parallel work | Yes. Native worktrees and cloud tasks | Yes. Multiple terminal instances |
| Config file | AGENTS.md | CLAUDE.md |
| Non-tech friendly | Yes. Buttons, previews, visual UI | More technical. Better for experienced users. |
The most effective approach is not to pick one tool. They are genuinely complementary, and knowing when to hand off between them is what separates a good AI workflow from a great one.
How a complete build goes from first idea to deployed product using both tools.
| Codex | Stage | Claude Code |
|---|---|---|
| Write prompt in plain English. Describe what you want to build. | IDEA | Start a new Claude Code session. Describe architecture goals. |
| Hit Shift+Tab for Plan Mode. Codex maps files and approach. | PLAN | Ask Claude to reason through architecture and edge cases. |
| Approve the plan. Codex writes files and runs tests. | BUILD | Claude executes multi-file changes with full context. |
| Open Code Review panel. Click lines, request changes. | REVIEW | Review output in terminal. Ask Claude to adjust inline. |
| Codex runs tests automatically. Use gh-fix-ci skill for CI. | TEST | Claude reasons through failures. Better on complex logic bugs. |
| Use Vercel plugin or Codex Cloud to deploy from app. | SHIP | Claude handles deployment scripts and config files. |
An Electron app that looks like a coding environment. Best starting point for non-technical users. Visual UI, image previews, built-in git, and inline code review.
openai.com/codexInstall Codex as a VS Code extension if you already use VS Code. It runs directly inside your existing setup.
Install via terminal: npm i -g @openai/codex. For users comfortable with the command line.
Run tasks on OpenAI's servers. Start a job, close your laptop, come back to a finished result. Requires GitHub connected.
Find the download button. Choose Mac or Windows. The file is around 150MB. The install takes about one minute with no setup decisions to make.
Codex runs on your existing ChatGPT subscription: Plus ($20/mo), Pro ($100/mo), Business, or Enterprise. Free accounts have a limited trial window. Use the same email as ChatGPT.
Codex asks for read and write access. You can allow once or always. Codex only works inside the project folder you choose — it does not read other files on your computer.
In ChatGPT, go to Settings > Data Controls > Export Data. OpenAI emails you a zip with every past conversation. Paste a short summary of the most relevant ones into your first Codex thread as context. Three sentences about your business and goals is enough.
This is the most important concept to understand before you start building. Get this right and everything else clicks.
| One project per client | Keep each client's work isolated so the agent only has relevant context |
| One project per product | Your website is one project. Your app is another. |
| One project per automation | A recurring email workflow lives in its own project |
| One project per tool | A proposal generator, a content calendar — each gets its own folder |
Inside each project you create threads. A thread is one conversation about one specific task. Hit Ctrl+N to create a new thread.
/compact to summarise it and keep the context clean./fork to explore a different direction without touching the original thread.On your desktop or Documents, create a new folder. Name it clearly: 'my-website', 'client-smith', or 'content-tools'. In Codex hit Cmd+O and select that folder. It appears in your sidebar.
With your project selected, hit Ctrl+N. A blank thread opens. This is your workspace for one task.
Hit Shift+Tab. You will see Plan Mode activate at the top. Always do this before asking Codex to build anything. It makes Codex outline the approach before touching any files. Skipping this is the number one beginner mistake.
Goal, context, constraints, done when. Example: "Goal: build a single-page website for my photography business. Context: brand colour is dark green, logo is in this folder. Constraints: plain HTML only. Done when the page loads with a working contact form."
Codex produces a written plan. Read it. If anything looks wrong, say so before approving. Once you approve, it starts building.
When finished, hit Cmd+Option+B to open the code review panel. You see exactly what changed. Click any line and ask for adjustments in plain English.
| Pillar | What to include | Example |
|---|---|---|
| Goal | What are you trying to achieve? | Build a landing page for my photography business with a contact form |
| Context | What files, folders, or background info? | Brand colours are red and black. Logo is in the /assets folder |
| Constraints | What rules or limits should Codex follow? | Use plain HTML and CSS only. No frameworks |
| Done when | How will Codex know it succeeded? | Done when the page loads without errors and the form submits |
Codex is included with your existing ChatGPT subscription. There is no separate purchase.
| Plan | Monthly Cost | What You Get | Best For |
|---|---|---|---|
| Free | $0 | Limited trial access | Testing it out |
| Plus | $20/mo | Standard usage window, all core features | Individuals and freelancers |
| Pro | $100/mo | Higher usage limits, priority access | Power users and small teams |
| Business / Enterprise | Custom | Team management, SSO, data privacy controls | Companies and organisations |
/status inside Codex.| Codex CAN do this well | Codex CANNOT do this |
|---|---|
| Build websites, apps, tools, and dashboards from a description | Read your mind. Be specific about what you want. |
| Read, summarise, rewrite, and analyse documents and data files | Access the internet in real time unless you connect a web search MCP |
| Write, run, and fix code across many programming languages | Guarantee bug-free code. Always review what it builds. |
| Connect to external services like Gmail, Slack, and Google Calendar via MCP | Work on files outside your project folder unless you add them |
| Schedule and automate recurring tasks and workflows | Deploy to a live server without a plugin like Vercel (you need to set that up first) |
| Draft emails, proposals, content, and reports from templates | Remember things between sessions unless you use AGENTS.md or provide context |
| Manage your GitHub: commit, push, create pull requests, fix CI | Replace your own judgment. Review every significant piece of output before publishing. |
MCP stands for Model Context Protocol. In plain English: it is how you give Codex the ability to talk to other apps and services.
Without MCP, Codex only knows about the files in your project folder. With MCP, Codex can read your emails, check your calendar, post to Slack, search the web, talk to your database, and much more. Think of MCP connectors like apps on a phone — install the ones you need and Codex gains those powers.
| Connector | What Codex can do with it |
|---|---|
| Gmail | Read emails, draft replies, categorise inbox, send messages |
| Google Calendar | Read today's events, create new events, reschedule meetings |
| Slack | Send messages, read channel history, post summaries |
| GitHub | Commit code, open pull requests, read issues, fix CI failures |
| Figma | Read design files and translate them into working code |
| Notion / Google Drive | Read documents, create pages, update databases |
| Web Search | Search the internet for real-time information during a task |
To install: open Codex, click the puzzle icon in the sidebar to open the MCP marketplace. Find the connector you want and click Install.
AGENTS.md is a simple text file that lives in your project folder. Every time Codex starts a new thread in that project, it reads this file first. It is how you give Codex standing instructions that never need repeating.
| Category | Example |
|---|---|
| Project overview | This is a website for a photography business in Auckland. The audience is brides and event planners. |
| Tech stack | We use plain HTML, CSS, and vanilla JavaScript only. No frameworks. |
| Brand rules | Primary colour is #2D4A3E. Font is Inter. Logo is always in the top left. |
| Tone of voice | Write copy in a warm, professional tone. No jargon. Short sentences. |
| Do not touch | Never modify the /legacy folder. Never change the homepage hero image. |
| Build command | Run 'npm run build' to test. Run 'npm run deploy' to publish. |
| What happened | What to do |
|---|---|
| Codex went in the wrong direction | Stop it immediately. Type 'stop' or close the thread. Open the Code Review panel (Cmd+Option+B), revert the changes, then start a new thread with a clearer prompt. Next time, use Plan Mode first. |
| The output looks wrong or broken | Do not accept it. Tell Codex specifically what is wrong: "The button is overlapping the text on mobile. Fix only that." Be specific. Vague feedback produces vague fixes. |
| Codex seems stuck or keeps looping | Type /compact to summarise the thread and free up context. If still stuck, fork the thread with /fork and try a different approach. |
| You hit your usage limit | Check your window at chatgpt.com/codex/settings/usage. Switch to the Mini model to stretch your remaining budget. Your limit resets on a rolling 5-hour and weekly basis. |
| A file got changed that you did not want changed | Open the Code Review panel (Cmd+Option+B). Find the file. Click Revert on that specific file. |
| Codex cannot find a file you mentioned | The file must be inside the project folder. If it is elsewhere on your computer, move it or copy it into the folder first, then ask again. |
Five things a non-technical person could build with Codex from scratch.
Skills are reusable instruction files stored at ~/.agents/skills/ that Codex loads automatically. Install via the Skills Marketplace (puzzle icon) or type $skill-installer [name].
| Skill | What it does | Why it matters |
|---|---|---|
create-plan | Forces Codex to produce a written implementation plan before it opens a single file. | Prevents the wrong-direction session that wastes time and tokens. Start here. |
WarpGrep | A search subagent that runs 8 parallel code searches at once. | Finds things in your codebase in ~5 seconds instead of 75 seconds. |
gh-fix-ci | Reads failing GitHub Actions logs and automatically writes the fix. | Turns a 45-minute debugging loop into a background task. |
gh-address-comments | Reads every PR review comment and addresses them all in one session. | The review-response cycle is where development velocity goes to die. |
frontend-skill | Overrides generic AI design decisions. Forces a real colour palette and typography choice. | Without it, Codex builds UIs that work. With it, they look like someone made a decision. |
stop-slop | Strips AI writing patterns from READMEs, docs, and commit messages. | The code can be excellent and still feel hollow because the docs were generated. |
/modelsSwitch AI model or reasoning level/compactSummarise a long thread/forkBranch a conversation without touching the original$skill-nameRun or install a skill