Engineering Craft › Clean Code & Principles

KISS (Keep It Simple)

Prefer the simplest solution that works.

Also known as: Keep It Simple, Keep It Simple Stupid, keep it simple

KISS (“Keep It Simple, Stupid”) means: of the solutions that work, pick the simplest one. Simple code has fewer places for bugs to hide, is quicker to understand and is cheaper to change.

# Clever
def is_even(n):
    return not (n & 1) if isinstance(n, int) else (_ for _ in ()).throw(TypeError)

# Simple
def is_even(n):
    return n % 2 == 0

What simple means

Simple is not the same as easy or short. A one-line regex that nobody can read is easy to write but not simple. A clear ten-line loop may be simpler than a dense chain of tricks.

Simple means:

• few moving parts and little hidden behavior,
• one obvious way to follow what happens,
• no machinery you don’t need.

How it shows up

• Use a plain function before inventing a class hierarchy.
• Use the language’s standard features before adding a library, and a library before building your own.
• Don’t add configuration, plugin systems or layers “in case”. See YAGNI.
• Pick boring, proven technology unless there’s a real reason not to.
• Prefer a small copy-paste now over a premature abstraction (see premature abstraction).

Watch out

Simplicity is a trade-off, not an absolute rule. Some problems really are complex, such as money, time zones or permissions, and a too-simple solution that mishandles them isn’t KISS, it’s wrong. The aim is no unnecessary complexity.

Test: can a teammate who has never seen this code explain what it does after reading it once? If not, simplify. See readability.