Available parameters and response documentation is available here

GET /lookup/chr19:20082943:1:G
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json ;utf-8
ETag: "fdd3c5fc8f50d075d71f7b010e047b1f40d604bcd94732237a807e5fbe0c0dd6"
Vary: Accept

{
  "chromosome": "chr19",
  "alt": "G",
  "ref": "T",
  "pos": 20082943,
  "variant_id": "10190190200829430003",
  "variant_type": "SNV",
  "cytobands": "19p12",
  "publication_counts": null
}