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Codex

Made Crystal Clear

By Christophe Paka · Updated October 23, 2026

A Visual Beginner's Guide to OpenAI's Coding Agent in the CLI, IDE, and Cloud

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Who this book is for

In plain words: Codex is OpenAI's coding agent: you describe a task, it writes the code, runs the tests, and hands you a change to review.

  • Developers who want to hand off real coding tasks
  • Tech leads and engineering managers deciding how to use AI on code
  • Not for: Not for you if you don't work with code. Try AI Made Crystal Clear.

An agent that edits your code is only useful if you stay in control of what ships. This visual beginner's guide to Codex, OpenAI's coding agent, shows you how. Inside, you will learn to run a first supervised session in the app, the CLI or your editor, with an undo you control; set approvals and the sandbox so Codex asks when it should; write an AGENTS.md briefing that every session reads; delegate tasks to Codex Cloud and put code review on every pull request; pick the model and reasoning effort that fit your plan's five hour and weekly limits; and compare Codex with other coding agents on your own repository, with a test you can rerun. Fourteen chapters, 38 diagrams and 22 step by step recipes. Every idea has a diagram, every recipe is numbered with the result you should see, and every chapter ends with a Try it to check yourself. The words stay plain, and the real terms stay in. Whether you are a developer, a non coder building an app, a tech lead or an engineering manager, one habit runs through the book: judge the diff, never the summary.

Pages
206
Level
Beginner to advanced
Updated
October 23, 2026

12 real pages. Click a page to enlarge it.

Page 8: three ways to work with an AI
Page 19: one agent, many surfaces
Page 22: the surface decision map
Page 42: five rings around the agent
Page 60: anatomy of a working AGENTS.md
Page 80: start at the closest orbit that fits the task
Page 85: two meters, not one
Page 102: the internet access setting
Page 113: p0 and P1 findings reach the thread
Page 134: four layers, one session
Page 137: a permission profile holds three drawers of rules
Page 161: the plan ladder

Inside the book

  1. 01From Autocomplete to Delegation
  2. 02One Agent, Many Surfaces
  3. 03Your First Session, and the Undo Button
  4. 04Approvals and the Sandbox: What Codex May Do
  5. 05AGENTS.md, the Standing Briefing
  6. 06Pairing: The Interactive Loop
  7. 07Models, Effort, and Your Usage Budget
  8. 08Delegating to Codex Cloud
  9. 09Code Review on Every Pull Request
  10. 10Running an Agent Team
  11. 11Power Configuration and the Team Baseline
  12. 12Codex, Claude Code, or Cursor?
  13. 13The Business Case: Plans, Credits, Data and ROI
  14. 14Your 90 Days, Cheat Sheet and Resources

You'll leave with

  • See how one agent spans the CLI, the IDE, the app, the cloud, and code review
  • Commit before every task so the undo stays in your hands
  • Set approvals and the sandbox so a fooled agent stays harmless
Christophe Paka, author of Codex Made Crystal Clear

About the author

Christophe Paka writes every book on the shelf. He spent years in technical support at Salesforce and Microsoft, where the job was to make complex systems clear to customers who needed them working the same day. He has since built and run software as a founder and lead developer, worked as a Salesforce consultant, and grown a YouTube channel on tech careers past one million views.

This book was last updated on October 23, 2026.

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For teams

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Sources

Every source cited in Codex Made Crystal Clear. Each number matches the [n] marker next to that link in the book's "Go deeper" lists, so you can trace any claim back to its origin.

  1. [1]Codex documentation hub
  2. [2]openai/codex on GitHub
  3. [3]Codex quickstart
  4. [4]Codex pricing and plans
  5. [5]Wikipedia: Codex (AI agent)
  6. [6]Simon Willison on GPT-5-Codex
  7. [7]Builder.io: Codex vs Claude Code
  8. [8]Codex CLI guide
Show all 75 sources
  1. [9]IDE extension guide
  2. [10]Codex cloud guide
  3. [11]GitHub code review docs
  4. [12]Authentication docs
  5. [13]Sandboxing and approvals
  6. [14]Codex changelog
  7. [15]Installing Codex CLI on Windows, 2026 guide
  8. [16]developers.openai.com/codex/agent-configuration/agents-md
  9. [17]developers.openai.com/codex/config-file/config-reference
  10. [18]developers.openai.com/codex/prompting
  11. [19]agents.md
  12. [20]builder.io/blog/agents-md
  13. [21]addyosmani.com/blog/code-agent-orchestra
  14. [22]Developer commands reference
  15. [23]VS Code Marketplace listing (openai.chatgpt)
  16. [24]developers.openai.com/codex/models
  17. [25]openai.com/index/gpt-6-astra
  18. [26]help.openai.com article 11369540
  19. [27]simonwillison.net/2025/Dec/19/introducing-gpt-52-codex
  20. [28]developers.openai.com/codex/environments/cloud-environment
  21. [29]developers.openai.com/codex/cloud/internet-access
  22. [30]chatgpt.com/codex/settings/environments
  23. [31]github.com/openai/codex-universal
  24. [32]zackproser.com/blog/openai-codex-review-2026
  25. [33]chatgpt.com/codex/settings/code-review
  26. [34]openai.com/index/codex-security-now-in-research-preview/
  27. [35]Codex SDK
  28. [36]Enterprise admin setup
  29. [37]Gartner 2026: Leader in enterprise coding agents
  30. [38]OpenAI trust portal
  31. [39]Codex CLI on Windows: native sandbox vs WSL
  32. [40]Codex docs: Cloud environments (new experience)
  33. [41]Codex docs: Code review
  34. [42]Codex docs: Speed (Fast and Ultrafast)
  35. [43]Codex docs: Sandboxing
  36. [44]Codex docs: Permission modes
  37. [45]Codex docs: Developer commands (CLI)
  38. [46]Codex docs: What's new
  39. [47]Codex docs: Windows sandbox
  40. [48]Codex docs: Managed configuration
  41. [49]Codex docs: Codex Security overview
  42. [50]Codex docs: Models and Trusted Access (cyber safety)
  43. [51]Codex docs: dots, getting started
  44. [52]openai/codex releases
  45. [53]Codex CLI 0.161.0 release notes
  46. [54]Codex CLI 0.163.0 release notes
  47. [55]Unite.AI: OpenAI unveils GPT-6.1 Sol at DevDay with new Codex and ChatGPT tools
  48. [56]Constellation Research: OpenAI touts 5 million weekly Codex users
  49. [57]SentinelOne: CVE-2026-14898, Codex macOS app information disclosure
  50. [58]ThaiCERT: Critical Codex vulnerability, GitHub token theft via Unicode injection
  51. [59]GitLab Advisory Database: CVE-2025-61260, @openai/codex
  52. [60]git restore (git-scm.com)
  53. [61]git init (git-scm.com)
  54. [62]First time Git setup, Pro Git (git-scm.com)
  55. [63]git reflog (git-scm.com)
  56. [64]git add (git-scm.com)
  57. [65]Spend limits (OpenAI API docs)
  58. [66]Slash commands in Codex CLI
  59. [67]Codex docs: Subagents
  60. [68]Codex docs: Git worktrees
  61. [69]git-scm.com: git-worktree
  62. [70]Codex docs: Import from other agents
  63. [71]OpenAI Status
  64. [72]r/codex on Reddit
  65. [73]OpenAI Developer Community forum
  66. [74]Codex docs: dots
  67. [75]Codex docs: Auto-review

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