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Codex CLI
Agentic Engineering from First Principles
This book is 100% completeLast updated on 2026-06-21
The definitive guide to agentic software engineering with Codex CLI, from prompting and AGENTS.md fundamentals to multi-agent orchestration, CI/CD integration, security hardening, and enterprise deployment across 28 hands-on chapters.
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About
About the Book
Codex CLI: Agentic Engineering from First Principles is the most comprehensive guide to agentic software engineering with OpenAI's command-line coding agent. Across 28 chapters in six parts, you'll move from first principles to production workflows and team-scale practice: prompting and AGENTS.md configuration, approval modes and kernel-level sandboxing, model selection, context and cost management, MCP servers, hooks, skills, sub-agents and orchestration, worktrees, CI/CD integration, security hardening, and enterprise deployment. Later chapters cover debugging and testing agentic workflows, AI code review, practical engineering guides (codebase migration, backend, frontend, and infrastructure as code), and the bigger picture: benchmarks, competing tools, harness engineering, and how to structure an agentic engineering team.
Whether you're a solo developer looking to multiply your output or an engineering lead rolling out agentic workflows across a team, this book gives you the mental models and practical techniques to work effectively with AI coding agents.
Written by Daniel Vaughan and drawing on real-world experience and community insights, it equips every chapter with learning objectives, worked examples, and hands-on exercises.
Author
About the Author
Daniel Vaughan
Daniel Vaughan is a technology leader and software architect based in the United Kingdom, specialising in agentic AI. He has spent approaching thirty years across enterprise, startup, and academic settings, with a career-long focus on engineering quality and developer productivity. His work now centres on the shift where AI stops being an experiment and becomes core to how organisations build software.
Daniel is Head of Forward Deployed Engineering at HCLTech AI Labs, where he leads a global practice embedding engineers and coding agents inside complex enterprise environments to take production AI from prototype to live systems. He built the practice from the ground up, running lean regional pods in which a shared architect, a small number of engineers, and a team of agents working through tools such as Codex, Claude Code, Cursor, and GitHub Copilot deliver at the output of a much larger team.
Before HCLTech AI Labs, Daniel was director of software engineering at Mastercard in London, leading cloud strategy and architecture for real-time payment products in a highly regulated financial services environment. Earlier, he spent eight years at the European Bioinformatics Institute in Cambridge, moving from software engineer into engineering leadership, working on the same problems of software quality and developer productivity that he now solves with agentic tooling.
He is the author of Cloud Native Development with Google Cloud (O'Reilly, 2024) and Ext GWT 2.0: Beginner's Guide (Packt, 2010), a Google Developer Expert, and a Green Software Champion. He writes about agentic engineering and AI-assisted development at blog.danielvaughan.com.
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