# Interpolation

> Double-brace placeholders inside catalog values get filled at render time. Missing params resolve to an empty string — never a stray brace in the UI.

Source: https://ngwr.dev/guides/translations/interpolation  
Kind: Service

## Catalog shape

Use double braces around the param name — any string-coercible value (string, number, boolean) is rendered as-is. Objects fall back to `JSON.stringify`.

```typescript
{
  "app": {
    "title": "Welcome",
    "hello": "Hello, {{name}}!",
    "items": "{{count}} item(s) selected"
  }
}
```

## Live

The same key, two locales, one input — type your name to see the placeholder resolve in real time.

```angular-html
<p>{{ 'app.hello' | wrT: { name: user().name } }}</p>
<p>{{ 'app.items' | wrT: { count: selection().length } }}</p>
```

## Reusable formatter

`useI18nFormatter(key)` returns a `(params) => string` helper — handy when the same parametrized label gets reused inside expressions.

```typescript
import { useI18nFormatter } from 'ngwr/i18n';

const formatItems = useI18nFormatter('app.items');
// formatItems({ count: 3 }) → '3 item(s) selected'
```