# CDT Formation

CDT Formation endpoints return the **schema definitions** for Custom Data Types — the structure, fields, and field types defined in Welkin Designer. Use these to understand the shape of CDT records before reading or writing data via the [Custom Data Types (CDT)](/developer-and-integration-guide/api-reference/custom-data-types.md) endpoints.

**Base path:** `/{tenantName}/{instanceName}/formation/cdts`

***

## Endpoints

### GET Get One CDT

**GET** `/{tenantName}/{instanceName}/formation/cdts/{cdtName}`

Returns the schema definition for a single Custom Data Type by name.

#### Path Parameters

| Parameter | Type   | Required | Description                            |
| --------- | ------ | -------- | -------------------------------------- |
| `cdtName` | string | Yes      | The CDT name as configured in Designer |

#### Example Request

```http
GET /acme-health/live/formation/cdts/vitals
Authorization: Bearer <token>
```

#### Example Response `200 OK`

```json
{
  "name": "vitals",
  "label": "Vitals",
  "fields": [
    { "name": "bloodPressure", "label": "Blood Pressure", "type": "STRING" },
    { "name": "heartRate", "label": "Heart Rate", "type": "NUMBER" },
    { "name": "recordedAt", "label": "Recorded At", "type": "DATETIME" }
  ]
}
```

***

### GET Get All CDTs

**GET** `/{tenantName}/{instanceName}/formation/cdts`

Returns schema definitions for all Custom Data Types configured in your Welkin instance.

#### Query Parameters

| Parameter | Type    | Default | Description      |
| --------- | ------- | ------- | ---------------- |
| `page`    | integer | `0`     | Page number      |
| `size`    | integer | `20`    | Results per page |

#### Example Request

```http
GET /acme-health/live/formation/cdts
Authorization: Bearer <token>
```


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