You can tailor the JSON Rich Text Editor (RTE) to meet specific content needs by enabling the Custom Editor. This allows selecting formatting options and controlling the toolbar for content managers.
Note: Only the stack Owner, Admins, and users with Developer role can customize the JSON RTE field.
To customize the JSON RTE, log in to your Contentstack account and perform the steps given below:

Content managers will see the configured toolbar options when creating or editing entries of this content type.

Additional Resources:
Use the following API requests to manage JSON RTE via Content Management API.
You can also retrieve JSON RTE fields via GraphQL. Refer to the Get JSON RTE Fields while Retrieving Entries query in the GraphQL API documentation.