curl --request GET \
  --url https://toncenter.com/api/v3/masterchainInfo

{
  "first": {
    "after_merge": true,
    "after_split": true,
    "before_split": true,
    "created_by": "<string>",
    "end_lt": "0",
    "file_hash": "<string>",
    "flags": 123,
    "gen_catchain_seqno": 123,
    "gen_utime": "0",
    "global_id": 123,
    "key_block": true,
    "master_ref_seqno": 123,
    "masterchain_block_ref": {
      "seqno": 123,
      "shard": "0",
      "workchain": 123
    },
    "min_ref_mc_seqno": 123,
    "prev_blocks": [
      {
        "seqno": 123,
        "shard": "0",
        "workchain": 123
      }
    ],
    "prev_key_block_seqno": 123,
    "rand_seed": "<string>",
    "root_hash": "<string>",
    "seqno": 123,
    "shard": "0",
    "start_lt": "0",
    "tx_count": 123,
    "validator_list_hash_short": 123,
    "version": 123,
    "vert_seqno": 123,
    "vert_seqno_incr": true,
    "want_merge": true,
    "want_split": true,
    "workchain": 123
  },
  "last": {
    "after_merge": true,
    "after_split": true,
    "before_split": true,
    "created_by": "<string>",
    "end_lt": "0",
    "file_hash": "<string>",
    "flags": 123,
    "gen_catchain_seqno": 123,
    "gen_utime": "0",
    "global_id": 123,
    "key_block": true,
    "master_ref_seqno": 123,
    "masterchain_block_ref": {
      "seqno": 123,
      "shard": "0",
      "workchain": 123
    },
    "min_ref_mc_seqno": 123,
    "prev_blocks": [
      {
        "seqno": 123,
        "shard": "0",
        "workchain": 123
      }
    ],
    "prev_key_block_seqno": 123,
    "rand_seed": "<string>",
    "root_hash": "<string>",
    "seqno": 123,
    "shard": "0",
    "start_lt": "0",
    "tx_count": 123,
    "validator_list_hash_short": 123,
    "version": 123,
    "vert_seqno": 123,
    "vert_seqno_incr": true,
    "want_merge": true,
    "want_split": true,
    "workchain": 123
  }
}

{
  "code": 123,
  "error": "<string>"
}