Available parameters and response documentation is available here

GET /lookup/chr12:25398284:C:T?format=api
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json ;utf-8
ETag: "d1f261d225448e39caa7e294640432baf2a5f8afecc53192d6ac0da43cf68161"
Vary: Accept

{
  "chromosome": "chr12",
  "alt": "T",
  "ref": "C",
  "pos": 25398284,
  "variant_id": "10190120253982840004",
  "variant_type": "SNV",
  "cytobands": "12p12.1",
  "publication_counts": null
}