Supermarket websites and Google for me, but after a while for things I generally eat I know what and approximately how much I'm able to eat, so rarely need to check any more.
Some of the possible issues with the carbs, etc management databases are that different countries use different methods of calculating carbs - e.g. in the UK we count starch and sugar as total carbs content and count fibre separately, but USA includes fiber in their total, and calls sugar/starch content net carbs. So you need to know which system applies, and where people input their own info which version they've used can make a difference. Sometimes too data can be omitted if people don't know or don't consider them relevant, which may result also in misleading information.
