This is the sample config file: test1: abc: abc: - sdhfg test1: - def test1: ghi: - sdjfhgsdj - sdgfgsd ghi: - rty - weytr test2: - jkl No i dont have control over the config file. Other users who use my software may have config files with duplicate keys. Such is the case which i want to catch and error out. The structure is very complex to define and there are lot of config files with lots of keys. So will have to form another hash key values and then loop over each task to find its duplicate. This extra processing can be avoided if YAML or any other config file reader gave error for duplicate keys