How to assign a Clio task template to a matter via API: key facts explained

Applying a Clio task template list to a matter via API is done through the matter endpoints — either POST /matters.json or PATCH /matters/{id}.json — using a nested task_template_list_instances array, not through any task template resource endpoint. The /task_template_list path offers no method to assign a list to a matter, and the copy endpoint only duplicates lists without linking them to matters. Because task_template_list_instances are write-only and absent from matter response schemas, there is no direct API way to check whether a list has already been applied, requiring developers to reconcile by querying filtered tasks. This write-only limitation makes idempotency a developer responsibility, as the API will not prevent a checklist from being assigned twice if a PATCH request fires more than once. Developers should account for the trigger logic, guard checks, and reconciliation work, as what appears to be a simple integration typically takes two to four days to build correctly.