Thin, all the way through

Think of it when a feature touches several layers, or a plan says “first all the database work, then all the screens”.

In everyday life

Like cooking one full plate of a new dish before you cook for 200 guests. Each part tasted fine alone; the plate shows that the sauce and the rice do not go together.

One case

A team adds gift cards to a shop. They build the database for 3 weeks, the server for 2 weeks, then the checkout screen for 2 weeks. In week 7 they connect the layers for the first time, and the server rejects every card code the screen sends. One thin slice in week 1, a single $10 card bought and spent, would have shown the mismatch.

Thin, all the way through
The ideaKeep it small
Thin, all the way through

Build one thin piece of a feature through every layer, from the screen to the database, and prove it works. Then build the next piece.

Keep it small, Habits

Every case

Each layer can look finished on its own and still fail where it meets the next one. Those meeting points hold most of the surprises: formats, names, missing fields. Work done one layer at a time finds all of them at the end, when every layer is already built on the wrong guess. A thin slice through every layer finds the first surprise in days, while a change of course is still cheap.

The word

Engineers call this

vertical sliceBuild one thin piece of a feature through every layerOne level of a program, such as the screen, the server or the database. Each layer passes work to the next., from the screen to the database, and prove it works. Then build the next piece.

Make the first piece thin and complete: one path, every layer, proven to work. Widen it only after that.

Where this idea leads

Skills that encode it

  • to-tickets Matt PocockEach ticket is a tracer bullet: a narrow but complete path through every layer, demoable or verifiable on its own.
  • tdd Matt PocockWork in vertical slices: one test, one implementation, repeat. Writing all the tests first is an anti-pattern.