Finding Validation Rules using Tooling API

gistfile1.txt

Apex Code:

HttpRequest req = new HttpRequest();
req.setHeader('Authorization', 'Bearer ' + UserInfo.getSessionID());
req.setHeader('Content-Type', 'application/json');
String domainUrl=URL.getSalesforceBaseUrl().toExternalForm();
system.debug('********domainUrl:'+domainUrl);
req.setEndpoint(domainUrl+'/services/data/v33.0/tooling/query/?q=Select+id,FullName,TableEnumOrId,ValidationName,Metadata+from+ValidationRule');
req.setMethod('GET');
Http h = new Http();
HttpResponse res = h.send(req);
system.debug(res.getBody()); 
String ss=res.getBody();

Response will be in JSON format:

{
    "size": "22",
    "totalSize": "22",
    "done": "true",
    "entityTypeName": "ValidationFormula",
    "records": {
      "attributes": {
        "type": "ValidationRule",
        "url": "/services/data/v33.0/tooling/sobjects/ValidationRule/03d900000007XP3AAM"
      },
      "Id": "03d900000007XP3AAM",
      "FullName": "SDRelationship__c.SDOC__GD_Link",
      "TableEnumOrId": "01I90000000nEcaEAE",
      "ValidationName": "GD_Link",
      "Metadata": {
        "errorConditionFormula": "
				AND(
				 ISPICKVAL(SDOC__SDoc_Rel_GD_Status__c, 'Linked to Google Doc')
				,
				ISBLANK( SDOC__SDoc_Rel_GD_Link__c )
			)",
        "errorMessage": "Before you are able to manually set the Docs Status to \"Linked to Google Doc\", you must first enter a valid URL to an existing Google Doc in the Google Docs Link field.",
        "active": "true"
      }
    }
  }
  
  Here TableEnumOrId takes 15 or 18 digit id of custom object or API name of standard objects