Thank you @CharlieAnderson for raising this to the devs 
A “feature request” and maybe “common use case” could look like:
- In order to filter assets of a specific folder by custom criteria
- the user should know possible custom possibilites
- by requesting
/metadata
- a list of all possible custom (and standard) “keyword”-tags of that folder should be returned as json object (similar to requesting a single /metadata of an asset
- the user should be able to filter/search assets by given criteria (eg:
/children?filter={field_definition_id=[xxx,yyy],status=approved}
etc…
I tried to figure out, how the Web-UI is getting these data shown here:
It seems that this goes to a graphql request, but I can’t do that against the regular API.
It would be nice, to have access to all the custom fields (and metafields) to prefill forms without overheating the API. like so:
{
"data": {
"custom_fields": [
{
"value": [
{
"id": "6404e3d2-7ba7-4d06-8209-5a16ce1eee2a",
"display_name": "TikTok"
},
{
"id": "2559bff7-0011-486d-8108-b3043935a2c5",
"display_name": "Facebook"
},
{
"id": "bf8fbfbd-bb21-41d4-9da9-29f1e8a0747a",
"display_name": "Instagram"
}
],
"field_type": "select_multi",
"field_definition_id": "3ce109fc-40c5-4ef2-895f-44275ec3ee26",
"field_definition_name": "Social Media Target",
"field_options": [
{
"id": "6404e3d2-7ba7-4d06-8209-5a16ce1eee2a",
"display_name": "TikTok"
},
{
"id": "bf8fbfbd-bb21-41d4-9da9-29f1e8a0747a",
"display_name": "Instagram"
},
{
"id": "2559bff7-0011-486d-8108-b3043935a2c5",
"display_name": "Facebook"
},
{
"id": "4b6f18b8-cdde-4834-a761-7ac613b70087",
"display_name": "Twitter"
}
]
}
],
"essentials": [
{
"value": 1,
"field_type": "rating",
"field_definition_id": "4109f4b9-aee7-47f8-8daa-bdc8b2283bc3",
"field_definition_name": "Rating"
},
{
"value": [
{
"id": "0ac56323-1569-496a-93ab-e83e20390106",
"display_name": "supershot"
}
],
"field_type": "select_multi",
"field_definition_id": "6c6cd6a4-ba14-4d06-bdee-4f4ac8bbe524",
"field_definition_name": "Keywords",
"field_options": [
{
"id": "0ac56323-1569-496a-93ab-e83e20390106",
"display_name": "supershot"
},
{
"id": "d40ea7f0-60e5-44ca-a199-8523a5c90457",
"display_name": "demo"
},
{
"id": "4c31f6b0-bf40-44ac-abf8-bc2527dabf3f",
"display_name": "closeup"
}
]
}
],
Thank you for reading.. 
have anice day