Systematic Debugging

Iron Law

No fixes without root cause investigation first.

Never fix the symptom. Never add a workaround. Find where the invalid data originated and fix it there.

Four Phases

1. Reproduce — Make it fail consistently

• Read the error message carefully (the FULL message)
• Write a failing test that demonstrates the bug
• Check git log for recent changes near the failure
• If intermittent: gather diagnostic evidence, check timing assumptions

2. Analyze — Find working examples