This guide introduces how data is input to and output from Shopify Functions.

<aside class="note">
<h4>Functions availability</h4>
<ul>
    <li>Users that have <a href="/docs/storefronts/themes/architecture/layouts/checkout-liquid"><code>checkout.liquid</code></a> customizations need to <a href="https://help.shopify.com/manual/checkout-settings/checkout-extensibility/checkout-upgrade">upgrade to Checkout Extensibility</a> to use Function APIs.</li>
    <li>Stores on any plan can use public apps that are distributed through the Shopify App Store and contain functions. Only stores on a <a href="https://help.shopify.com/manual/intro-to-shopify/pricing-plans/plans-features/shopify-plus-plan">Shopify Plus plan</a> can use <a href="https://help.shopify.com/manual/apps/app-types/custom-apps">custom apps</a> that contain <a href="/docs/api/functions">Shopify Function APIs</a>.</li>
    <li>Some Shopify Functions capabilities are available only to stores on a <a href="https://help.shopify.com/manual/intro-to-shopify/pricing-plans/plans-features/shopify-plus-plan">Shopify Plus plan</a>. See <a href="/docs/api/functions#availability-of-shopify-functions">Shopify Function APIs</a> for details.</li>
</ul>
</aside>


## How it works

Shopify Functions query [input data](#input) from the schema of a [Function API](/docs/api/functions/). The [output](#output) is also defined by the same Function API schema. Function output is a declarative object which represents operations for Shopify to execute.

Shopify passes input as JSON to your function using `STDIN`, and your function writes output as JSON to Shopify using `STDOUT`. Refer to the [WebAssembly API](/docs/apps/build/functions/programming-languages/webassembly-for-functions) for details.

## Input

You can specify what input your function needs using an input query. For example, the structure of the JSON in the [input example](#input-example) matches the shape of the following query:

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</div>

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

<script type="text/plain" data-language="graphql">
RAW_MD_CONTENT{
  cart {
    buyerIdentity {
      email
    }
  }
}
END_RAW_MD_CONTENT</script>

</div>
</p>


When you create a function, Shopify CLI generates a GraphQL file for your input query. You can edit the query to request the exact data you need. Each [target](/docs/apps/build/app-extensions/configure-app-extensions#targets) implemented in your function extension can have a unique input query.

### Input example

The following example shows an input that retrieves a customer's email:

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</div>
</div>

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

<script type="text/plain" data-language="json">
RAW_MD_CONTENT{
  "cart": {
    "buyerIdentity": {
      "email": "hello@example.com"
    }
  }
}
END_RAW_MD_CONTENT</script>

</div>
</p>


The [Function API references](/docs/api/functions) provide information on the available fields for the input query.

## Output

Each Function API [extension target](/docs/apps/build/app-extensions/configure-app-extensions#targets) specifies the shape of the function's output using a GraphQL type. For example, there's a `FunctionRunResult` definition for the `purchase.order-discount.run` target of the [Order Discount API](/docs/api/functions/reference/order-discounts/graphql/functionrunresult).

> Note:
> Functions created in API version 2023-07 or earlier can use the `FunctionResult` type, which is available for backwards compatibility.

If a function discounts an order by $50.00, then it could return the following output:

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

<script type="text/plain" data-language="json">
RAW_MD_CONTENT{
  "discounts": [{
      "message": "$50.00 off",
      "targets": [{ "orderSubtotal": { "excludedVariantIds": [] } }],
      "value": { "fixedAmount": { "amount": "50.0" } }
  }],
  "discountApplicationStrategy": "FIRST"
}
END_RAW_MD_CONTENT</script>

</div>
</p>


The [Function API references](/docs/api/functions) provide information on available targets, and their associated output GraphQL type.

## GraphQL schema

Each Function API has a GraphQL schema representation, which you can use to improve your development workflow. For example, a GraphQL schema can be used with:

- The [VSCode GraphQL plugin](https://marketplace.visualstudio.com/items?itemName=GraphQL.vscode-graphql)
- Language-specific code generation tools, such as [`graphql_client`](https://github.com/graphql-rust/graphql-client) for Rust

On creation, each function includes a copy of the GraphQL schema in the `schema.graphql` file.

### Generating the latest schema

If you're using an unstable API version, then the GraphQL schema might have changed since you created the function or last generated the schema. If you change your target API version, then the Function API schema might have changed between versions.

To generate the latest GraphQL schema for your function, use the [`function schema` command](/docs/api/shopify-cli/app/app-function-schema). This command outputs the latest schema based on your function's API type and version to the `schema.graphql` file:

```bash
shopify app function schema
```

You can output the generated GraphQL schema to `STDOUT` by passing the `--stdout` flag:

```bash
shopify app function schema --stdout
```

You can also save the output to a different file or pipe it into a code generation tool, if needed:

```bash
 shopify app function schema --stdout > <FILE_PATH>
```

## API versions

Function APIs are [versioned](/docs/api/usage/versioning). Updates are released quarterly and supported API versions are listed in the [release notes](/docs/api/release-notes).
 You can update to a new version of a Function API by completing the following steps:

1. Update the version of the API specified in your [configuration file](/docs/api/functions/configuration):

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    <script data-option="filename" data-value="shopify.extension.toml"></script>

    <script type="text/plain" data-language="toml">
    RAW_MD_CONTENTapi_version = "2023-10"
    END_RAW_MD_CONTENT</script>

    </div>
    </p>


1. [Generate the latest schema](#generating-the-latest-schema).

1. If you're using JavaScript, then run the following command to regenerate types based on your input query:

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    <script type="text/plain" data-language="bash">
    RAW_MD_CONTENTshopify app function typegen
    END_RAW_MD_CONTENT</script>

    </div>
    </p>



## Limitations

The following limitations apply to input queries:

- The maximum size for an input query, excluding comments, is 3000 bytes.
- Metafields with values exceeding 10,000 bytes in size will not be returned.
- Field arguments and input query variables of [list](https://graphql.org/learn/schema/#lists-and-non-null) type can't exceed 100 elements.
- Function input queries can have a maximum calculated query cost of 30. The following table describes the input query field costs for functions:

    | Field | Example | Cost value |
    |---|---|---|
    | `__typename` | | 0 |
    | Any field that returns a `Metafield` object | `metafield` on a `Product` object | 3 |
    | Any field on a `Metafield` object | `value` | 0 |
    | `hasAnyTag` | | 3 |
    | `hasTags` | | 3 |
    | Any field on a  `HasTagResponse` object | `hasTag` | 0 |
    | `inAnyCollection` | | 3 |
    | `inCollections` | | 3 |
    | Any field on a `CollectionMembership` object | `isMember` | 0 |
    | Other leaf nodes | `id` or `sku` on a `ProductVariant` object | 1 |

## Next steps

- Learn how [input queries and metafields](/docs/apps/build/functions/input-output/metafields-for-input-queries) work in Shopify Functions.
- Learn how to [use variables in input queries](/docs/apps/build/functions/input-output/use-variables-input-queries) with Shopify Functions.