Keep Getting Error “Bad Message 431”

This happened to me today (Chrome - Developer Console)

The issue was I had lots of code from previous Execute Anonymous sessions that had been commented out. As I added new lines to the top such as below, I pushed the character limit as sent via Tooling API past the max value

   Lead[] leads = new list { new Lead(Company = 'Foo00', LastName = 'LName00'), new Lead(Company = 'Foo01', LastName = 'LName01') }; insert leads; leads[0].Company = 'Foo00Changed'; leads[1].Company = 'Foo01Changed'; leads[1].Website = 'www.failme.com'; // force partial success by failing this in VR Database.SaveResult[] results = Database.update(leads,false); // allow partial success /* many lines of code previously entered for prior tests. "Many" was in the hundreds */

By deleting some of those lines of commented out code, you can resolve http error 431.