# $parameter

## Import

```typescript
import { $parameter } from "alepha/api/parameters";
```

## Overview

Declares a named, schema-validated runtime parameter - configuration that
lives in the database, is editable from the admin UI, and is versioned with
`rollback()`. Read it with `get()`; every change records who made it.

## Options

| Option        | Type             | Required | Description                                              |
| ------------- | ---------------- | -------- | -------------------------------------------------------- |
| `name`        | `string`         | No       | Parameter name using dot notation for tree hierarchy     |
| `description` | `string`         | No       | Human-readable description of the parameter.             |
| `schema`      | `T`              | Yes      | Zod schema defining the parameter structure.             |
| `default`     | `Infer<T>` | Yes      | Default value used when no parameter exists in database. |
| `migrate`     | `Object`         | No       | Optional migration function for schema changes           |

## Examples

```typescript
class FeatureFlags {
  checkout = $parameter({
    name: "checkout.flags",
    schema: z.object({ oneClick: z.boolean() }),
    default: { oneClick: false },
  });

  async isOneClickEnabled() {
    return (await this.checkout.get()).oneClick;
  }
}
```