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

# Create randomizer

> Create a weighted split test over existing questions or groups

Creates a randomizer from content that already exists in the study. Each arm shows one question or one existing question group; when an arm lists several `question_ids`, they are moved into a new group for that arm automatically. An arm may be left empty as a placeholder, but every arm needs a target before participants can be routed to it.

<ParamField body="study_id" type="string" required>The study ID.</ParamField>
<ParamField body="name" type="string" required>Internal name, e.g. `"Concept test"`.</ParamField>

<ParamField body="arms" type="array" required>
  2 to 12 arms. Each arm: `label` (string), `weight_basis_points` (integer, 1–10000; all arms must total exactly 10000), and one of `question_ids` (array of question IDs), `question_id` (a single question), or `question_group_id` (an existing group), or none of them for an empty arm.
</ParamField>

<ParamField body="display_order" type="integer">Top-level position after the arm content is moved into the arms. Omit to append.</ParamField>

### Response

`201` with the created randomizer, same shape as [List randomizers](/api-reference/randomizers/list-randomizers).

<Warning>
  A question or group can belong to only one arm, and logic rules must never jump between arms — a participant only ever sees one.
</Warning>

<RequestExample>
  ```bash cURL theme={null}
  curl -X POST https://api.getversive.com/api/v1/randomizers \
    -H "Authorization: Bearer $VERSIVE_API_KEY" \
    -H "Content-Type: application/json" \
    -d '{
      "study_id": "9b2f7c1e-4a4b-4f6e-9a1d-1c2d3e4f5a6b",
      "name": "Concept test",
      "arms": [
        { "label": "Concept A", "weight_basis_points": 5000, "question_ids": ["c1d2e3f4-0000-4000-8000-000000000001"] },
        { "label": "Concept B", "weight_basis_points": 5000, "question_group_id": "d4e5f6a7-0000-4000-8000-000000000002" }
      ]
    }'
  ```
</RequestExample>