---
name: rule-of-three
description: Structure complexity into about three memorable chunks with a rhythm - the phone-number principle - for systems, workflows, names, and output.
---

# Rule of Three

## Use This Skill When

Designing or naming a system, workflow, API, or process; deciding how many sections, steps, phases,
or options to present; or organizing output that is getting hard to hold.

## The phone number

A US phone number is ten digits, but nobody remembers ten digits — they remember three chunks: area
code, prefix, line number. `(931) 381-XXXX`. Two things make it stick:

1. **Chunking.** Ten digits broken into three sections is far easier to memorize than ten in a row.
   Grouping reduces cognitive load — the same reason card numbers and IDs are spaced, not run together.
2. **Rhythm.** Three chunks give it a cadence you can say aloud — one-two-three. That beat is why
   three-part phrases land and repeat: _Veni, vidi, vici_; _stop, drop, and roll_; _Post. Build. Ship._

Structure things the same way: take complexity, chunk it into about three sections, and make the
three say with a rhythm.

## Why it works

Three is the sweet spot — enough to be complete (beginning / middle / end; propose / act / verify),
few enough to stay memorable, hold a beat, and let you do each part well.

## Apply

- Group a flat list of many items into ~three sections — ten digits into three chunks.
- Give a system three top-level parts and name them as verbs or roles you can say in one breath.
- When something feels sprawling, ask "what are the three?" before adding more structure.

## Resist the fourth

A fourth top-level chunk usually means the model is wrong — fold it into one of the three, or rethink
the decomposition. It also breaks the rhythm. Equally, do not force three where it is artificial;
three is a strong default, not a law.

## Evidence in this codebase

Post.Bid.Ship. Post.Build.Ship. architect / developer / gatekeeper. frontier / workhorse / light.
workflow / guidance / reference. Threes — because they are easy to hold, easy to say, and easy to do
well.