The Validation API enables you to provide your own validation of a cart and checkout.

## Extension targets

The Validation API exposes the following [targets](/docs/apps/build/app-extensions/configure-app-extensions#targets):

| Target | Output type | Description |
| ------ | ----------- | ----------- |
| `purchase.validation.fetch` | [FunctionFetchResult](/docs/api/functions/reference/cart-checkout-validation/graphql/functionfetchresult) | See [Network access for Shopify Function](/docs/apps/build/functions/input-output/network-access) |
| `purchase.validation.run` | [FunctionRunResult](#functionrunresult) | Outputs the list of validation errors |

## Input

The `RunInput` object is the complete schema that your function can receive as [input](/docs/apps/build/functions/input-output#input).


For a list of fields that the Validation API's `Input` object accepts, refer to [Input](/docs/api/functions/reference/cart-checkout-validation/graphql/input).

### Example

The following example shows an input query:


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</div>
</div>

<script data-option="filename" data-value="input.graphql"></script>

<script type="text/plain" data-language="graphql">
RAW_MD_CONTENTquery Input {
  cart {
    lines {
      quantity
    }
  }
}
END_RAW_MD_CONTENT</script>

</div>
</p>


The following example shows the resulting input to the query:


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</div>

<script data-option="filename" data-value="input.json"></script>

<script type="text/plain" data-language="json">
RAW_MD_CONTENT{
  "cart": {
    "lines": {
      "quantity": 2
    }
  }
}
END_RAW_MD_CONTENT</script>

</div>
</p>


## FunctionRunResult

The [`FunctionRunResult`](/docs/api/functions/reference/cart-checkout-validation/graphql/functionrunresult) object is the expected [output](/docs/apps/build/functions/input-output#output) for the `purchase.validation.run` target.

### Example

The following function result shows errors that block a customer from proceeding through checkout.

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<script data-option="filename" data-value="output.json"></script>

<script type="text/plain" data-language="json">
RAW_MD_CONTENT
{
  "errors": [
    {
      "localized_message": "Not possible to order more than one of each",
      "target": "$.cart"
    }
  ]
}
END_RAW_MD_CONTENT</script>

</div>
</p>


### Supported checkout field targets

The following checkout UI fields can be targeted with an error message. The `target` property follows the input query's data structure.

<table>
  <caption>List of checkout field targets</caption>
  <tr>
    <th scope="col" style="width:50vw">Field</th>
    <th scope="col" style="width:50vw">Target value</th>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/cart"><code>cart</code></a></td>
    <td><code>$.cart</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/buyeridentity"><code>email</code></a></td>
    <td><code>$.cart.buyerIdentity.email</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/buyeridentity"><code>phone</code></a></td>
    <td><code>$.cart.buyerIdentity.phone</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>address1</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.address1</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>address2</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.address2</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>city</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.city</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>company</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.company</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>countryCode</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.countryCode</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>firstName</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.firstName</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>lastName</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.lastName</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>phone</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.phone</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>provinceCode</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.provinceCode</code><td>
  </tr>
  <tr>
    <td><a href="/docs/api/functions/reference/cart-checkout-validation/graphql/common-objects/mailingaddress"><code>zip</code></a></td>
    <td><code>$.cart.deliveryGroups[0].deliveryAddress.zip</code><td>
  </tr>
</table>