# Create Custom Field Definition Custom Fields allow you to add extra information about your contacts to your contact database. With custom fields, you can create custom segments from your individual contacts or from your contact database that will dynamically update your content with the values for the individual contact receiving the email. Your custom fields are completely customizable to the use cases and user information that you need. You can also manage your Custom Fields using the [Custom Fields UI in the Marketing Campaigns App](https://mc.sendgrid.com/custom-fields). For more about creating Custom Fields, including a list of Reserved Fields, see our [Custom Fields documentation](/docs/sendgrid/ui/managing-contacts/custom-fields/). ## Operation overview ```json {"path":"https://api.sendgrid.com/v3/marketing/field_definitions","method":"post","servers":[{"url":"https://api.sendgrid.com","description":"The Twilio SendGrid v3 API"}]} ``` **This endpoint creates a new custom field definition.** Custom field definitions are created with the given `name` and `field_type`. Although field names are stored in a case-sensitive manner, all field names must be case-insensitively unique. This means you may create a field named `CamelCase` or `camelcase`, but not both. Additionally, a Custom Field name cannot collide with any Reserved Field names. You should save the returned `id` value in order to update or delete the field at a later date. You can have up to 500 custom fields. The custom field name should be created using only alphanumeric characters (A-Z and 0-9) and underscores (\_). Custom fields can only begin with letters A-Z or underscores (\_). The field type can be date, text, or number fields. The field type is important for creating segments from your contact database. **Note: Creating a custom field that begins with a number will cause issues with sending in Marketing Campaigns.** ## Operation details ### Authentication API Key ### Headers ```json [{"in":"header","name":"Authorization","required":true,"default":"Bearer <>","schema":{"type":"string"}}] ``` ### Request body ```json {"schema":{"type":"object","required":["name","field_type"],"example":{"name":"custom_field_name","field_type":"Text"},"properties":{"name":{"type":"string","minLength":1,"maxLength":100},"field_type":{"type":"string","enum":["Text","Number","Date"],"refName":"FieldType","modelName":"FieldType"}}},"encodingType":"application/json"} ``` ### Responses ```json [{"responseCode":"200","schema":{"description":"","content":{"application/json":{"schema":{"type":"object","required":["field_type","id","name"],"properties":{"id":{"type":"string"},"name":{"type":"string","minLength":1,"maxLength":100},"field_type":{"type":"string","enum":["Text","Number","Date"],"refName":"FieldType2","modelName":"FieldType2"},"_metadata":{"title":"_metadata","type":"object","refName":"Metadata","modelName":"Metadata","properties":{"prev":{"type":"string","format":"uri"},"self":{"type":"string","format":"uri"},"next":{"type":"string","format":"uri"},"count":{"type":"integer","minimum":0}}}}},"examples":{"response":{"value":{"id":"a1_T","name":"custom_field_name","field_type":"Text","_metadata":{"self":"https://api.sendgrid.com/v3/marketing/field_definitions/a1_B"}}}}}}}},{"responseCode":"400","schema":{"description":"","content":{"application/json":{"schema":{"type":"object","required":["errors"],"properties":{"errors":{"type":"array","uniqueItems":true,"items":{"title":"error","type":"object","required":["message"],"refName":"CustomFieldsError","modelName":"CustomFieldsError","properties":{"message":{"type":"string"},"field":{"type":"string"},"error_id":{"type":"string"},"parameter":{"type":"string"}}}}}}}}}}] ``` Create Custom Field Definition ```js const client = require("@sendgrid/client"); client.setApiKey(process.env.SENDGRID_API_KEY); const data = { name: "My_Custom_Field", field_type: "Text", }; const request = { url: `/v3/marketing/field_definitions`, method: "POST", body: data, }; client .request(request) .then(([response, body]) => { console.log(response.statusCode); console.log(response.body); }) .catch((error) => { console.error(error); }); ``` ```python import os from sendgrid import SendGridAPIClient sg = SendGridAPIClient(os.environ.get("SENDGRID_API_KEY")) data = {"name": "My_Custom_Field", "field_type": "Text"} response = sg.client.marketing.field_definitions.post(request_body=data) print(response.status_code) print(response.body) print(response.headers) ``` ```csharp using System; using System.Collections.Generic; using System.Threading.Tasks; using SendGrid; public class Program { public static async Task Main() { string apiKey = Environment.GetEnvironmentVariable("SENDGRID_API_KEY"); var client = new SendGridClient(apiKey); var data = @"{ ""name"": ""My_Custom_Field"", ""field_type"": ""Text"" }"; var response = await client.RequestAsync( method: SendGridClient.Method.POST, urlPath: "marketing/field_definitions", requestBody: data); Console.WriteLine(response.StatusCode); Console.WriteLine(response.Body.ReadAsStringAsync().Result); Console.WriteLine(response.Headers.ToString()); } } ``` ```java import com.sendgrid.*; import java.io.IOException; import org.json.JSONObject; import java.util.HashMap; import java.util.Arrays; public class Example { public static void main(String[] args) throws IOException { try { SendGrid sg = new SendGrid(System.getenv("SENDGRID_API_KEY")); Request request = new Request(); request.setMethod(Method.POST); request.setEndpoint("/marketing/field_definitions"); request.setBody(new JSONObject(new HashMap() { { put("name", "My_Custom_Field"); put("field_type", "Text"); } }).toString()); Response response = sg.api(request); System.out.println(response.getStatusCode()); System.out.println(response.getBody()); System.out.println(response.getHeaders()); } catch (IOException ex) { throw ex; } } } ``` ```go package main import ( "fmt" "github.com/sendgrid/sendgrid-go" "os" ) func main() { apiKey := os.Getenv("SENDGRID_API_KEY") host := "https://api.sendgrid.com" request := sendgrid.GetRequest(apiKey, "/v3/marketing/field_definitions", host) request.Method = "POST" request.Body = []byte(`{ "name": "My_Custom_Field", "field_type": "Text" }`) response, err := sendgrid.API(request) if err != nil { fmt.Println(err.Error()) os.Exit(1) } else { fmt.Println(response.StatusCode) fmt.Println(response.Body) fmt.Println(response.Headers) } } ``` ```php /sendgrid-php.php'; $apiKey = getenv("SENDGRID_API_KEY"); $sg = new \SendGrid($apiKey); $request_body = json_decode('{ "name": "My_Custom_Field", "field_type": "Text" }'); try { $response = $sg->client ->marketing() ->field_definitions() ->post($request_body); print $response->statusCode() . "\n"; print_r($response->headers()); print $response->body() . "\n"; } catch (Exception $ex) { echo "Caught exception: " . $ex->getMessage(); } ``` ```ruby require 'sendgrid-ruby' include SendGrid sg = SendGrid::API.new(api_key: ENV['SENDGRID_API_KEY']) data = JSON.parse('{ "name": "My_Custom_Field", "field_type": "Text" }') response = sg.client.marketing.field_definitions.post(request_body: data) puts response.status_code puts response.headers puts response.body ``` ```bash curl -X POST "https://api.sendgrid.com/v3/marketing/field_definitions" \ --header "Authorization: Bearer $SENDGRID_API_KEY" \ --header "Content-Type: application/json" \ --data '{"name": "My_Custom_Field", "field_type": "Text"}' ```