I recently needed to create a rich text field in a SharePoint list programatically. Since I am using REST all over the place, it would be practical to continue that now as well.

I was able to find out how to create a new field. It is done by posting to this url:

For example like this:

$.ajax({

  url: reqUrl,

  type: "POST",

  data: "{ '__metadata': { 'type': 'SP.Field' }, 'Title': 'Comments', 'FieldTypeKind': 3 }",

  headers: { 

    "X-RequestDigest": <form digest value>,

    "accept": "application/json; odata=verbose",

    "content-type": "application/json;odata=verbose",

    "content-length": <length of body data>

  },

  success: successHandler,

  error: errorHandler

});

Note the FieldTypeKind which is set to 3, which refers to the multi line text field. 

The problem is that by default, the field is created as a plain text field. I needed rich text, so I started searching for a solution. I did not get many hits. I found some hints, e.g. there seems to be a "RichText" property that seems promising:

But I was not sure how to use it.

Finally, I found the solution in the Fields REST API reference (see "MERGE request example")

By slightly modifying this example, I was able to make it work. I already tried adding 'RichText': true to my data object, but got an error message. The key point here is that you need to combine RichText=true with the type "SP.FieldMultiLineText" instead of the regular "SP.Field".

The final result of my reqData variable:

This shows not only how to create rich text fields, but how to set other field properties as well (this link, remember?) It seems there are a rich set of properties accessible to those who need to create complex schemas.