Convert CSV to JSON without uploading the file

A conversion like this sits between an export and an import: a product catalogue moving between systems, a member list going into a new platform, a batch of transactions being reconciled. A bad conversion becomes a bad import, and a bad import becomes a support queue full of people whose records are now wrong. Keeping the file off a third party's machine is the easy part; getting the types right is the work.

Types are where data is lost silently. A value like 007312 is an identifier, and the moment it is treated as a number the leading zeros are gone for good. The same applies to postcodes, account numbers and phone numbers with a country prefix. Decide what each column actually is before you convert, and quote anything that is an identifier rather than a quantity.

Dates are worse than numbers, because a CSV date carries no format and no timezone: 03/04 is two different days depending on who wrote it. Fix a single unambiguous format on the way in and check a row you know. Going the other direction, remember that JSON nests and CSV does not, so nested objects and arrays have to be flattened into columns before a spreadsheet can hold them.

Do the conversion with the network disconnected the first time. It works, and once you have seen a large export convert offline you have the answer for the next time somebody asks whether the customer list went anywhere. A hosted converter that is still spinning when you pull the network has already told you where the file went.