List custom fields for segment criteria

GET

/api/v3/contacts/custom-fields/segment-criteria

const url = 'https://api.tryletterhead.com/api/v3/contacts/custom-fields/segment-criteria?api=true';
const options = {method: 'GET', headers: {Authorization: 'Bearer <token>'}};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}

curl --request GET \
  --url 'https://api.tryletterhead.com/api/v3/contacts/custom-fields/segment-criteria?api=true' \
  --header 'Authorization: Bearer <token>'

Lists the custom fields available to build segment criteria with — your company’s own custom fields, merged with Letterhead’s system-managed fields (mailbox provider, last-open date, and similar). Each entry carries a source of user or system so you can tell them apart. This is the catalog Create a segment and List segments’ criteria.conditions[].customFieldKey values are drawn from.

This is a company-level (v3) read. Authenticate with a company API key as a Bearer token.

Authorizations

bearerAuth

Parameters

Query Parameters

api

required

boolean

Required. Set to true.

Responses

200

200 OK

application/json

object

items

Array<object>

object

integer

name

string

label

string

type

string

required

boolean

sortOrder

integer

createdAt

string

updatedAt

string

source

user or system.

string

message

string

total

integer

Example

{
  "items": [
    {
      "id": 4,
      "name": "favoriteColor",
      "label": "Favorite color",
      "type": "text",
      "required": false,
      "sortOrder": 0,
      "createdAt": "2026-05-01T10:00:00+00:00",
      "updatedAt": "2026-05-01T10:00:00+00:00",
      "source": "user"
    },
    {
      "id": -3,
      "name": "__lh.mailboxProvider",
      "label": "Mailbox provider",
      "type": "text",
      "required": false,
      "sortOrder": 0,
      "createdAt": "",
      "updatedAt": "",
      "source": "system"
    }
  ],
  "message": "Segment criteria fields retrieved.",
  "total": 2
}

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