Documentation showing JSON types vs. Custom Field types?

[Dale Brubaker]

e.g. which become arrays? I know multiuserpicker comes through as an array, and Text doesn't. What about grouppicker? Each one I must learn by waiting for data to come through the REST GET. Is there a better way?

[Nic Brough [Adaptavist]]

Not if you want to interpret it in your program.

If you look at the UI though, you'll be able to work it out, and it's very rare that Atlassian change the "type" of field (I think the last one was the conversion to allow many components to be selected instead of one, and that was in JIRA 2 or 3.0)

Broadly though, you'll find date/time fields come out as date/time, free format text will be a single block of text, data that contains one item will be a single output, and multi-item ones will be arrays of single outputs.  If it's a "select" type field (and that includes radio buttons and single users), it's a single, and if it's multi-select (multi-check box, multi-user picker, multi-group picker, components, versions, etc, there's a bit of a clue in the name of most), you'll get an array