Run the following query to insert bogus data into your { external_functions } table: INSERT INTO `moodle`.`mdl_external_functions` (`name`, `classname`, `methodname`, `component`, `capabilities`) VALUES ('mod_invalid_get_foo', 'mod_invalid\\external\\get_foo', 'execute', 'mod_invalid', ''); Navigate to Server > Web services > API documentation in site administration Confirm presence of an error, which reads as follows: Coding error detected, it must be fixed by a programmer: Cannot find file /externallib.php with external function implementation for mod_invalid\external\get_foo::execute