Account Custom Button: Validate

// Establish a connection to the API,
// using the current session ID

{!REQUIRESCRIPT("/soap/ajax/29.0/connection.js")}
sforce.connection.sessionId = "{!$Api.Session_ID}";

// This button was created to attempt validation of an Account.
// All we have to do is instantiate the account in JavaScript,
// and set the IsValidating__c field to true, which we assume
// will set off the desired validation rule

var account = new sforce.SObject("Account");
account.Id = "{!Account.Id}";
account.IsValidating__c = true;

// Attempt to update the account record.
// This requires the account to be placed in an array, and
// the update results will similarly be given back in an array

var results = sforce.connection.update([account]);

// Examine the results to see whether our update was successful.
// If it was, then all is well. We will assume there is an associated
// workflow rule that will clear the IsValidating__c checkbox.

if (results[0].getBoolean("success")) {
    alert("Validation succeeded!");
}
else {
    alert("Validation failed...");
}