# Which TDD skill should you actually install?

Canonical URL: https://bestskillsforclaude.com/en/skills/tdd
Language: en
Skill: tdd
Publisher: Matt Pocock (https://github.com/mattpocock)
Source: https://github.com/mattpocock/skills
License as stated by the publisher: MIT
Runtime: Claude Code and agents that support the skills CLI
Category: Engineering discipline
Last reviewed: 2026-08-05

Two good options, and installing both is the one clear mistake.

## Short answer
Matt Pocock's tdd skill drives red, green, refactor one vertical slice at a time, meaning each cycle delivers a thin but complete piece of behaviour. It is lighter than the superpowers version and fits teams that want the discipline without adopting a whole methodology. Choose one of the two, because running both produces contradictory instructions.

Best for: Feature work where you want working behaviour end to end early, and a light process.
Skip it if: You already run superpowers, whose test-driven-development skill covers the same ground.

## What to remember
- Vertical slices keep the system runnable at every step.
- It is lighter than superpowers TDD, which suits teams that do not want a full methodology.
- Two TDD skills at once is a conflict, not a belt and braces setup.
- The refactor step is the one people skip, and the one that pays.

## What it changes in practice
Slicing vertically means each cycle produces something that runs, rather than a layer that only becomes useful once three more layers exist. With an agent that matters more than usual, because a half built layer cake is impossible to verify.
The narrower the slice, the more useful the cycle. A slice that takes six steps to pass has already stopped being a slice.

## Where it disappoints
It assumes a test setup that already works. In a codebase where running one test takes minutes, the loop is too slow to hold anyone's discipline.
It also does not decide what to build. Slicing well is a design skill that the process supports but does not supply.

## Install and first run
1. Install it with the skills CLI from mattpocock/skills, published under MIT.
2. Define the first slice narrowly enough that it can be finished in one cycle.
3. Refactor while the tests are green, never while they are red.

## Questions
### How is it different from the superpowers TDD skill?
It is lighter and slice oriented, while superpowers embeds TDD in a wider methodology with planning and verification skills around it.

### Can I install both?
You can, but you should not. They will give the agent conflicting instructions for the same job.

### What is a vertical slice?
A thin path through the whole system that actually runs, rather than one complete layer that does nothing on its own.

## Sources
- mattpocock/skills on GitHub: https://github.com/mattpocock/skills
- Agent skills directory listing: https://skills.sh

## Other languages
- Spanish: https://bestskillsforclaude.com/es/skills/tdd
- Brazilian Portuguese: https://bestskillsforclaude.com/pt-br/skills/tdd
- Japanese: https://bestskillsforclaude.com/ja/skills/tdd