Salesforce Validation Rule while inserting a text value error

You may use something like this:  IF(RIGHT(Text_Field_API__c , 4) == 'Text', true, false)

Hi HARSHITA,

Try this triggers code
trigger TextError on Account (before insert) {
public String res;
for(Account a:trigger.new)
{
res=a.name.right(4);
if(res!='text') {
a.addError('last 4 digits must text');
}
}
}