# best-practices

Simon Willison's Agentic Engineering Patterns guide now has 12 chapters — but this new one goes at the very beginning. He finally answers 'What is Agentic Engineering?' The answer is surprisingly simple: using coding agents to help build software. The interesting part is why it took 11 chapters of hands-on patterns before he felt ready to define it.

Simon Willison's Agentic Engineering Patterns — 'First Run the Tests': every time you start a new session, your first instruction should be to run the test suite. Four words, three ripple effects — the agent learns how to run tests, gauges the codebase size, and automatically shifts into a 'I should maintain tests' mindset.

Simon Willison's Agentic Engineering Patterns, Chapter 3: AI should help us ship better code, not worse. Technical debt cleanup costs near zero now, architecture decisions can be validated with prototypes instead of guesses, and quality compounds over time.

Simon Willison shared his agentic engineering playbook at the Pragmatic Summit — five tokens to start TDD, Showboat for manual verification, reverse-engineering six frameworks into a standard, and why bad code is a choice you make.

A guide to Codex best practices from prompting and planning to MCP, Skills, and Automations — building a more reliable agent workflow.

Simon Willison added an 'Anti-Patterns' section to his Agentic Engineering Patterns guide — and the first entry hits hard: don't submit AI-generated code you haven't personally verified. You're not saving time, you're stealing it from your reviewer. This post covers his principles, what a good agentic PR looks like, and a real terraform destroy horror story.

Simon Willison introduces Agentic Manual Testing: let AI agents manually operate code and UI like humans do, catching bugs that automated tests miss. With Playwright, Rodney, and Showboat, the 'tests pass but it's broken' nightmare becomes a thing of the past.

Chapter 5 of Simon Willison's Agentic Engineering Patterns: Interactive Explanations. Core thesis: instead of staring at AI-generated code trying to understand it, ask your agent to build an interactive animation that shows you how the algorithm works. Pay down cognitive debt visually.

Chapter 4 of Simon Willison's Agentic Engineering Patterns: Hoard Things You Know How to Do. Core thesis: every problem you've solved should leave behind working code, because coding agents can recombine your old solutions into things you never imagined.

Chapter 3 of Simon Willison's Agentic Engineering Patterns: the Linear Walkthrough pattern. This technique transforms even vibe-coded toy projects into valuable learning resources. Core trick: make the agent use sed/grep/cat to fetch code snippets, preventing hallucination.

Anthropic analyzed 9,830 Claude.ai conversations and defined 11 observable AI fluency behaviors. Key finding: people who iterate show 2x the fluency. But when AI produces beautiful artifacts, users question its reasoning less. The prettier the output, the more dangerous it gets.

Simon Willison launched a new series called Agentic Engineering Patterns — a playbook for working with coding agents like Claude Code and Codex. Lesson one: writing code got cheap, but writing good code is still expensive. Lesson two: 'red/green TDD' is the most powerful six-word spell for agent collaboration.

OpenAI released three primitives for long-running agents: Skills (reusable SKILL.md instruction packs), Shell (hosted container runtime), and Compaction (automatic context compression). Includes 10 battle-tested tips and Glean's production data.

StrongDM's AI team built a 'Software Factory' where AI agents write & review code. They clone apps into a 'Digital Twin Universe' for testing, an approach Simon Willison calls radical. At $10k/engineer/day in token costs, is it worth it?