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How-To SessionComplexity: HighAdvancedCodexVS CodeChatGPT Plus

How to Use Codex with ChatGPT Plus (VS Code or Codex App)

A technical workflow for connecting your ChatGPT account to Codex, operating in VS Code or the macOS Codex app, delegating cloud work, and shipping changes safely.

Stop: High-Complexity Technical Guide

This assumes you are comfortable with Git branches, repository-level permissions, command execution approvals, and code review discipline.

Quick Path

  • Confirm your ChatGPT Plus account is active and Codex is enabled.
  • Choose your surface: Codex app (macOS), VS Code extension, or both.
  • Select model class by task type: high-reasoning for architecture/debugging, balanced/default for most work, fast model for small edits.
  • Open a clean Git branch and define command/network guardrails before agent runs.
  • Use structured prompts with constraints, acceptance criteria, and test commands.
  • Delegate long-running tasks in Codex web when local focus matters.
  • Review all diffs, run tests, then merge via normal PR workflow.
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Step 1 — Confirm access model and choose your Codex surface

➡ What this step does

Codex access is tied to your ChatGPT plan. You need to verify plan eligibility first so sign-in works consistently across clients.

Then choose execution surface: VS Code extension for editor-first workflows, Codex app for multi-agent orchestration on macOS, and Codex web for delegated cloud tasks.

📋 What to do
  1. Verify your ChatGPT Plus subscription is active.
  2. Decide where you want to work first: VS Code or Codex app.
  3. Use the same ChatGPT account identity in every Codex surface to avoid split histories.
  4. Important: Codex threads/history are separate from regular ChatGPT app chats, so copy required context into Codex prompts.
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Expand to copy: Local branch + status precheck
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git status
git branch --show-current
✅ What should happen

You know exactly which account and client surface you are using.

Note: Codex conversation history is separate from standard ChatGPT chat history.

You can proceed to setup without plan/login confusion.

2

Step 2 — Prepare your local repository and safety guardrails

➡ What this step does

Agent output quality depends heavily on repository state and constraints. Start from a clean branch with clear acceptance criteria.

This prevents accidental edits on main and keeps every Codex run auditable in Git history.

📋 What to do
  1. Clone your repository and open a dedicated feature branch.
  2. Confirm current branch before allowing edits.
  3. Write explicit acceptance criteria in your issue/notes (scope, tests, non-goals).
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Expand to copy: Branch safety baseline
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git status
git checkout -b feat/codex-task
git branch --show-current
Expand to copy: Pre-task quality baseline
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npm install
npm run
npm run build
Expand to copy: If a test script exists
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npm test
✅ What should happen

You are on a non-main branch with a reproducible baseline.

Your repository is ready for controlled agent edits.

3

Step 3 — Set up the Codex macOS app

➡ What this step does

The Codex app is useful for running multiple agents and managing work in parallel with project-level controls.

Use this when you want strong separation between tasks and deeper agent orchestration than a single editor window.

📋 What to do
  1. Download and install the Codex app for macOS.
  2. Sign in with your ChatGPT account.
  3. Open your project folder/repository inside the app.
  4. Review sandbox and permission defaults before running first task.
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Expand to copy: Recommended first task prompt
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Read AGENTS.md and repository conventions first. Then summarize: 1) build/test commands, 2) branch strategy, 3) risky folders. Do not edit files yet.
✅ What should happen

The app opens your repository and can start tasks with your ChatGPT identity.

You understand when commands require explicit approval.

4

Step 4 — Set up Codex in VS Code

➡ What this step does

The VS Code route is optimal when you want Codex embedded in your daily editor loop for immediate file-level iteration.

Keep your integrated terminal visible so you can verify commands and test output as changes are made.

📋 What to do
  1. Open VS Code and install the Codex IDE extension.
  2. Authenticate using Sign in with ChatGPT.
  3. Open the same repository branch created in Step 2.
  4. Start with a small scoped task to validate end-to-end behavior.
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Expand to copy: Recommended first validation task
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Inspect this repo and identify the exact commands to run lint, typecheck, tests, and build. Do not edit code yet.
✅ What should happen

Codex can read and edit files in your open workspace.

You can run local tests in VS Code terminal against Codex-generated changes.

5

Step 5 — Select the right model for the task, then run high-signal prompts

➡ What this step does

Model choice affects speed, cost envelope, and reasoning depth. Pick model capability first, then send the task prompt.

Use high-reasoning models for deep analysis and risky edits, balanced/default models for most day-to-day implementation, and fast models for low-risk edits and quick iteration.

Treat prompts like engineering specs: objective, boundaries, required commands, and expected outputs.

📋 What to do
  1. For architecture/debugging/refactors across multiple files, select the highest reasoning model available in the Codex model picker.
  2. For normal feature work with tests and moderate scope, select the default/balanced model.
  3. For quick copy edits, small docs changes, and straightforward single-file updates, select the fastest model.
  4. Give Codex a precise task statement, not just a topic.
  5. Include constraints (no schema changes, no dependency upgrades, preserve API contracts, etc.).
  6. Require explicit validation commands and expected pass criteria.
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Expand to copy: Model selection cheat sheet
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Use high-reasoning model when: root-cause analysis, architecture tradeoffs, or high-risk refactors.
Use default/balanced model when: most implementation tasks with normal complexity.
Use fast model when: low-risk edits, formatting/docs cleanup, simple repetitive changes.
Expand to copy: Technical prompt template
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Task: <clear engineering objective>
Codebase context: <files/modules to inspect first>
Constraints: <what must not change>
Implementation requirements: <patterns/conventions>
Validation commands: <exact repo commands>
Acceptance criteria: <verifiable outcomes>
Output format: summarize edited files + risks + follow-up checks
✅ What should happen

Codex returns focused changes aligned with repo conventions.

You receive a concise summary of edits and validation status.

6

Step 6 — Delegate background tasks in Codex web when needed

➡ What this step does

Cloud delegation is useful for longer work items while you continue local development.

Use it for larger refactors, deep codebase audits, and draft PR proposals that you can pull down and review locally.

📋 What to do
  1. Open Codex web and connect GitHub if prompted.
  2. Delegate a specific task with scope boundaries and expected output.
  3. Review generated branch/PR artifacts before merging or pulling locally.
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Expand to copy: Cloud delegation task template
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Repository: <repo>
Branch target: <feature branch>
Task: <specific implementation>
Do not: modify CI config, dependencies, or unrelated files
Required output: changed files list, test/build results, and PR-ready summary
✅ What should happen

Task execution runs asynchronously in cloud sandbox context.

You can review resulting code and decide merge readiness with normal controls.

7

Step 7 — Review, test, and ship with normal engineering gates

➡ What this step does

Codex speeds implementation, but merge standards do not change. Every change still needs human review and test verification.

Use your existing pull-request workflow, required checks, and code-owner approvals.

📋 What to do
  1. Review full diff and ensure no out-of-scope files changed.
  2. Run build/tests/lint locally.
  3. Commit and push on feature branch.
  4. Open PR and request review as usual.
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Expand to copy: Final verification sequence
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git status
git diff
npm run build
npm test || echo "No test script or tests failed; investigate before merge"
git add .
git commit -m "feat: implement codex task"
git push -u origin $(git branch --show-current)
✅ What should happen

Your branch is fully reviewed and validated before merge.

Codex remains an accelerator, while human governance remains final gatekeeper.

Official References

Use these OpenAI primary sources for plan access, setup behavior, and client availability.

If UI steps differ over time, follow these references first.

OpenAI Help: Using Codex with your ChatGPT plan OpenAI Help: Codex CLI and Sign in with ChatGPT OpenAI: Codex product page OpenAI: Introducing the Codex app (macOS) OpenAI Codex CLI GitHub repository VS Code: extension management basics

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