The Custom field ID (e.g customfield_13244) is a unique identifier for a field that can be used in automation rules or to update field value via API.

There are a few ways to find the custom field ID:

Jira Settings

To find the ID of the custom field:

  1. Log in as a Jira Administrator.

  2. Go to Jira Settings > Issues > Custom fields.

  3. Search for the indicated custom field.

  4. Click the More menu (…) and select Edit Details.

  5. Copy the URL of the page. The URL will end with the ID number of the custom field.

Typing the following URL in the browser (changing it to your instance URL) will return the list of your custom fields for that instance

https://Your-Jira-URL/rest/api/2/field

REST API

There is also an API endpoint that allows getting the list of the custom fields along with their IDs: 

curl https://Your-Jira-URL/rest/api/2/field