KISS Principle

Keep It Simple, Stupid — coined by Kelly Johnson (Lockheed Skunk Works, 1960s). Systems work best when kept simple rather than made complicated. Every line of code is a liability.

Core Rules

1. Start with the naive solution — make it work, then evaluate if complexity is needed
2. One responsibility per component — agent, function, class, or module
3. Avoid premature abstraction — wait for 3+ concrete instances of duplication
4. Minimize dependencies — each is a liability and failure point
5. Explicit over implicit — no magic, no hidden behavior, no clever one-liners
6. Composable > hierarchical — flat function composition beats deep inheritance or state machines

KISS Decision Checklist

• Is this the simplest solution that correctly solves the problem?
• Would a junior developer understand this in under 2 minutes?
• Are we solving a real current problem or a hypothetical future one?
• Can anything be removed and still meet the requirement?
• Does this add a new dependency or moving part?
• Is the complexity proportional to the problem's scale?

Anti-Patterns (Non-KISS)

Related Principles

• YAGNI — You Aren't Gonna Need It (defer hypothetical features)
• DRY — eliminate duplication, but don't over-abstract to achieve it
• Unix Philosophy — do one thing well, compose small tools
• Occam's Razor — simplest explanation is usually correct