# Formatter and Checks

This note covers `16-formatter-and-checks/`, which exposes `formatter.<system>` and a small `checks.<system>.*` derivation that uses the same
formatter.

---

## 1. Why These Outputs Matter

Two flake outputs are especially practical in day-to-day use:

- `formatter.<system>`, which powers `nix fmt`, and
- `checks.<system>.*`, which powers `nix flake check`.

This example keeps both outputs small so the wiring is obvious.

---

## 2. The Important Connection

The flake points `formatter.<system>` at `pkgs.nixfmt`, then reuses that same formatter in a check:

```nix
formatter.${system} = pkgs.nixfmt;
```

That shows the main idea: a formatter output is just another derivation, so checks can use it too.

---

## 3. Commands to Try

```bash
cd 16-formatter-and-checks

nix fmt sample.nix
nix flake show
nix flake check
```