When you [create a post-purchase extension](/docs/apps/build/checkout/product-offers/build-a-post-purchase-offer), the `shopify.extension.toml` file is automatically generated in your extension directory. This guide describes the properties that you can configure in `shopify.extension.toml`.

## How it works

You define properties for your extension in the extension configuration file. The `shopify.extension.toml` file contains the extension's settings, which include the extension name and metafields.

When an extension is published to Shopify, the contents of the configuration file are pushed alongside the extension.

## Anatomy of a configuration file

The following example shows the properties in the `shopify.extension.toml` file:


```toml
type = "post_purchase"
name = "checkout_post_purchase"

# [[metafields]]
# namespace: my-namespace
# key: my-key

# [[metafields]]
# namespace: my-namespace
# key: my-key-2
```



| Property  | Required? | Description  |
|---|---|---|
| `type` | Yes | The type of extension. For checkout post-purchase extensions, this value is always `checkout_post_purchase`. |
| `name`  | Yes | The name of the checkout post-purchase extension. |
| `metafields`  | Yes | The [metafields](/docs/api/admin-graphql/latest/objects/metafield) that your extension needs to read. <br></br>You can specify up to five `key` and `namespace` pairs in the configuration file. When the extension is executed, Shopify looks for the metafields in each resource and returns their contents. |