Available parameters and response documentation is available here

GET /lookup/chr12:25398284:C:T
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json ;utf-8
ETag: "222dd46ad658a35dfa16e88fa0ceb2eada5e29f7f4643fa6c8dfb05c701134e0"
Vary: Accept

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