JQL
Get field reference data (GET)
Returns reference data for JQL searches. This is a downloadable version of the documentation provided in Advanced searching - fields reference and Advanced searching - functions reference, along with a list of JQL-reserved words. Use this information to assist with the programmatic creation of JQL queries or the validation of queries built in a custom query builder.
To filter visible field details by project or collapse non-unique fields by field type then Get field reference data (POST) can be used.
This operation can be accessed anonymously.
Permissions required: None.
get/rest/api/3/jql/autocompletedata
Response
Returned if the request is successful.