What JSON Lines is
JSON Lines is one complete JSON object per line, with no enclosing array and no commas between records. The file is not valid JSON as a whole, and that is the point.
Log pipelines, machine learning datasets and anything that appends records or reads them in a stream.
What Jira is
Jira wiki markup uses double pipes for header cells and single pipes for data cells.
Jira issues, comments and descriptions.
What changes when you convert JSON Lines to Jira
Each line is parsed on its own, so a corrupt record does not take the file with it. Keys are unioned across lines in first-seen order, so a record missing a field leaves that cell empty rather than shifting the columns.
Empty cells are filled with a single space, because a Jira row with two adjacent pipes collapses the column and shifts everything after it.
What carries over from JSON Lines to Jira
JSON Lines records 3 things about a table that Jira has no way to hold.
JSON Lines distinguishes a number from the text of a number; Jira does not, so every value arrives as text and has to be re-parsed by whatever reads it next.
An empty cell and a missing one are the same thing in Jira, so a null and an empty string in the JSON Lines both come out blank and can no longer be told apart.
JSON Lines can hold a value that is itself a list or an object. Jira has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
Jira marks header cells differently from data cells, so the keys are lifted out and written once as a marked header row rather than repeated on every row.
The identifier 007 comes out of the Jira as 007. Reading it as a number would have made it 7, and an id that changes value is worse than one that stays text.
The role "Analyst, data" survives with its comma, in one cell rather than split across two. That is the first thing to check in any converted table, and the usual place a Jira file goes wrong.
The quotes around Jonah "Jo" Pryce are left as a plain quote character in the Jira.