> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mercurjs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Create a variant axis

> Generate product variants from a multi_select axis attribute.

In this guide, you'll learn how to create a variant-axis attribute and use it to
generate a product's variants from server code.

A variant axis is a `multi_select` attribute with `is_variant_axis` set. Creating
one mirrors a native Medusa `ProductOption`, so the values a product selects along
the axis become the dimensions Medusa uses to generate variants.

## Create the axis attribute

```ts title="src/api/custom/attributes/route.ts" theme={null}
import type { MedusaRequest, MedusaResponse } from "@medusajs/framework/http"
import { createProductAttributesWorkflow } from "@mercurjs/core/workflows"

export async function POST(req: MedusaRequest, res: MedusaResponse) {
  const { result } = await createProductAttributesWorkflow(req.scope).run({
    input: {
      attributes: [
        {
          name: "Size",
          type: "multi_select",
          is_variant_axis: true,
          is_filterable: true,
          values: [{ name: "S" }, { name: "M" }, { name: "L" }],
        },
      ],
    },
  })

  res.status(201).json({ attribute: result[0] })
}
```

The workflow creates the `ProductAttribute`, a mirror `ProductOption`, and a
`ProductAttributeValue` for each option value. It wires `product_option_id` and
`product_option_value_id` behind the scenes.

## Attach it to a product

Attach the axis to a product and pass the subset of values that product offers.
Medusa generates a variant for each selected value.

```ts theme={null}
import { createAndLinkProductAttributesToProductWorkflow } from "@mercurjs/core/workflows"

await createAndLinkProductAttributesToProductWorkflow(req.scope).run({
  input: {
    product_id: "prod_shirt",
    add: [{ id: "pattr_size", value_ids: ["pattrval_s", "pattrval_m"] }],
  },
})
```

<Note>
  Only `multi_select` attributes can be variant axes. The `value_ids` you pass
  are the per-product subset of the axis's values. Only those become variants.
</Note>

## Inline axes

To create a product-scoped axis in the same step it's attached, pass the inline
form instead of an existing id. This creates an exclusive `ProductOption`, a
scoped attribute (`product_id` set), and the value mirror in one call:

```ts theme={null}
await createAndLinkProductAttributesToProductWorkflow(req.scope).run({
  input: {
    product_id: "prod_shirt",
    add: [{ title: "Cut", is_variant_axis: true, values: ["Slim", "Regular"] }],
  },
})
```

<Tip>
  Inline axes are ideal for a one-off dimension a single product needs. Reach for
  a global axis attribute when the same dimension, such as Size or Color, recurs
  across the catalog. See [Global vs inline](/platform/attribute/concepts/global-vs-inline).
</Tip>