Debugging: The 9 Indispensable Rules
David Agans' classic book on finding any bug in software or hardware, built around nine rules such as "make it fail", "quit thinking and look" and "if you didn't fix it, it ain't fixed", each illustrated with real war stories. The method it teaches is exactly what keeps AI-assisted debugging honest.
2002
Publisher listing · Sept 2026
Book
Other
David J. Agans
About a week of evening reading
All
Paid
What the book is
Debugging: The 9 Indispensable Rules for Finding Even the Most Elusive Software and Hardware Problems is a short, practical book by David J. Agans, first published in 2002. It does not teach a language or a tool. It teaches a method for finding the cause of any bug, and it has stayed in print because the method has not aged.
The nine rules
- Understand the system.
- Make it fail.
- Quit thinking and look.
- Divide and conquer.
- Change one thing at a time.
- Keep an audit trail.
- Check the plug.
- Get a fresh view.
- If you didn't fix it, it ain't fixed.
Each rule gets a chapter with war stories from real projects, most of them funny and memorable, which is why the rules stick.
Why it matters more with AI tools
AI tools are very good at proposing fixes and very bad at knowing whether a fix addressed the cause. The book's rules are the antidote. "Make it fail" means reproduce before asking for help. "Quit thinking and look" means gather evidence with logs and a debugger instead of accepting a plausible guess. "Change one thing at a time" means reject an AI change that touches ten things at once. And "if you didn't fix it, it ain't fixed" is exactly the problem with symptom patches, the empty catch blocks and retries that make an error disappear without removing the bug.
Is it worth your time?
Yes. It is quick to read, the ideas apply to every stack for your whole career, and it gives you names for habits you can then practise deliberately. Some examples are old hardware and early software, but the reasoning transfers directly. The author's website also offers a poster of the nine rules.
What you can do after it
- Reproduce a bug reliably before trying to fix it.
- Narrow a problem down by splitting the system in halves.
- Reject fixes you cannot explain.
- Keep a record of what you tried, so you and your tools stop repeating guesses.
How it fits the Coding with AI tools roadmap
The Sefism roadmap recommends it as the deeper read in the debugging stage, where you learn to use AI to widen your list of suspects rather than skip the investigation.
Common questions
Is it only for hardware engineers? No. It covers both, and software developers make up much of its readership.
Where can I buy it? The official site links to retailers; prices vary by format and region.
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