set_custom_field
Set or clear one of 15 custom field slots on a Kanban Tool task. Pair with list_custom_field_definitions to ensure value matches the field type.
Instructions
Set or clear one of the 15 custom_field_* slots on a task.
slot selects which numbered slot to write (1..15 inclusive — the
Kanban Tool API exposes exactly 15). Pair with
list_custom_field_definitions(board_id) to learn each slot's label
and type on a given board before writing.
value is sent verbatim — strings, numbers, and booleans all work.
Pass value=None to clear the slot: the wire body explicitly sends
null (not omits the key), and a subsequent get_task will see
custom_field_N: null. This differs from update_task semantics
where None means omit; for custom fields None means clear.
Common 422 (KanbanToolValidationError with parsed field_errors):
type mismatch — e.g. writing "hi" into a numeric slot, or a value
not in options for a dropdown-typed slot. Inspect the slot's
type/options via list_custom_field_definitions(board_id)
before writing if the slot purpose is uncertain.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| task_id | Yes | ||
| slot | Yes | ||
| value | Yes |
Output Schema
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | ||
| name | Yes | ||
| description | No | ||
| board_id | No | ||
| workflow_stage_id | No | ||
| swimlane_id | No | ||
| position | No | ||
| priority | No | ||
| color | No | ||
| due_date | No | ||
| start_date | No | ||
| tags | No | ||
| assigned_user_id | No | ||
| archived_at | No | ||
| block_reason | No | ||
| subtasks_count | No | ||
| subtasks | No | ||
| comments_count | No | ||
| timers_total | No | ||
| time_trackers | No | ||
| created_at | No | ||
| updated_at | No | ||
| size_estimate | No | ||
| size_estimate_description | No | ||
| time_estimate | No | ||
| search_tags | No | ||
| card_color | No | ||
| card_color_in_rgb | No | ||
| card_color_invert | No | ||
| card_type_id | No | ||
| recurring_schedule | No | ||
| reminders_schedule | No | ||
| linked_tasks | No | ||
| linked_tasks_status | No | ||
| task_dependencies | No | ||
| collaborators | No | ||
| attachments | No | ||
| attachments_count | No | ||
| created_by_id | No | ||
| moved_at | No | ||
| postponed_until | No | ||
| subtasks_completed_count | No | ||
| external_id | No | ||
| external_link | No | ||
| custom_fields | No | ||
| is_archived | Yes | True iff the task has an archival timestamp. | |
| is_blocked | Yes | True iff the task has a non-empty block reason. |