# !labels.keys

The `!labels.keys` YAML function returns the keys of the current component's own `metadata.labels`
as a sorted `[]string` — useful when a module or script wants a flat list of label names instead
of the full map (for example, an allow-list of label keys).

## Usage

The `!labels.keys` function takes no parameters:

```yaml
components:
  terraform:
    vpc:
      metadata:
        labels:
          Namespace: eg
          Environment: prod
          cost-center: platform
      vars:
        label_keys: !labels.keys
```

## Arguments

This function takes no arguments. It reads `metadata.labels` from the component it's used on.

## How It Works

`!labels.keys` reads the component's `metadata.labels` map and returns its keys as a `[]string`,
sorted alphabetically for deterministic output (Go map iteration order is randomized, so sorting
matters for reproducible plans). If `metadata.labels` is unset, `!labels.keys` returns an empty
list rather than an error.

## Examples

**File:** `stack.yaml`

```yaml
components:
  terraform:
    vpc:
      metadata:
        labels:
          Namespace: eg
          Environment: prod
          cost-center: platform
      vars:
        # label_keys will be ["Environment", "Namespace", "cost-center"] (sorted)
        label_keys: !labels.keys
```

## Related Functions

- [!labels](/functions/yaml/labels) - Get the current component's own `metadata.labels` as a map
- [!labels.values](/functions/yaml/labels.values) - Get the current component's `metadata.labels` values
- [!tags](/functions/yaml/tags) - Get the current component's own `metadata.tags` as a list