Can a new SObject type or new SObject field be created via the Tooling API?

Question

The Tooling API is great - very easy to use from Apex code by making HTTP calls containing straightforward JSON.

Two questions:

1. Is it still not possible to create a new SObject type e.g. MyNewCustomType__c?
   • see Possible to create a new sObject with Tooling API REST interface?
   • the CustomObject documentation does not list POST
2. Can a custom field be added to an already existing SObject type?
   • the CustomField documentation lists POST that makes me think the answer is "yes"

Answer 1

1. You still cannot create Custom Object with REST API, only with METADATA API.
2. Yes, you can create a Custom Field on existing sObject, request example:

HttpRequest request = new HttpRequest();
request.setHeader('Authorization', 'Bearer ' + UserInfo.getSessionID());
request.setHeader('Content-Type', 'application/json');
request.setEndpoint(URL.getSalesforceBaseUrl().toExternalForm()+'/services/data/v41.0/tooling/sobjects/CustomField/');
request.setMethod('POST');

String fieldLabel = 'New_Label';
String objectAPIName = 'Account';
String fieldAPIName = fieldLabel + '__c';

request.setBody('{"Metadata" : {"type" : "Text","description" : "", "inlineHelpText" : "","precision" : null,"label":"' + fieldLabel + '","length" : 255,"required" : false}, "FullName" : "'+objectAPIName+'.'+fieldAPIName+'"}');

Http http = new Http();
HTTPResponse res = http.send(request);
system.debug(res.getBody());