getblocktemplate

It returns data needed to construct a block to work on.

For full specification, see BIPs 22, 23, 9, and 145:

https://github.com/bitcoin/bips/blob/master/bip-0022.mediawiki
https://github.com/bitcoin/bips/blob/master/bip-0023.mediawiki
https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki#getblocktemplate_changes
https://github.com/bitcoin/bips/blob/master/bip-0145.mediawiki

Argument #1-template_request

Type: json object, Required

Description: Format of the template "rules": [ (json array, required) A list of strings "segwit", (string, required) (literal) indicates client side segwit support "str", (string) other client side supported softfork deployment ... ], "longpollid": "str", (string, optional) delay processing request until the result would vary significantly from the "longpollid" of a prior template "data": "hex", (string, optional) proposed block data to check, encoded in hexadecimal; valid only for mode="proposal" }

     {
       "mode": "str",          (string, optional) This must be set to "template", "proposal" (see BIP 23), or omitted
       "capabilities": [       (json array, optional) A list of strings
         "str",                (string) client side supported feature, 'longpoll', 'coinbasevalue', 'proposal', 'serverlist', 'workid'
         ...
       ],

Result---(If the proposal was accepted with mode=='proposal')

  null    (json null)

Result---(If the proposal was not accepted with mode=='proposal')

Type: string (hex)

Description: According to BIP22

Result---(Otherwise)

  {                                          (json object)
    "version" : n,                           (numeric) The preferred block version
    "rules" : [                              (json array) specific block rules that are to be enforced
      "str",                                 (string) name of a rule the client must understand to some extent; see BIP 9 for format
      ...
    ],
    "vbavailable" : {                        (json object) set of pending, supported versionbit (BIP 9) softfork deployments
      "rulename" : n,                        (numeric) identifies the bit number as indicating acceptance and readiness for the named softfork rule
      ...
    },
    "capabilities" : [                       (json array)
      "str",                                 (string) A supported feature, for example 'proposal'
      ...
    ],
    "vbrequired" : n,                        (numeric) bit mask of versionbits the server requires set in submissions
    "previousblockhash" : "str",             (string) The hash of current highest block
    "transactions" : [                       (json array) contents of non-coinbase transactions that should be included in the next block
      {                                      (json object)
        "data" : "hex",                      (string) transaction data encoded in hexadecimal (byte-for-byte)
        "txid" : "hex",                      (string) transaction id encoded in little-endian hexadecimal
        "hash" : "hex",                      (string) hash encoded in little-endian hexadecimal (including witness data)
        "depends" : [                        (json array) array of numbers
          n,                                 (numeric) transactions before this one (by 1-based index in 'transactions' list) that must be present in the final block if this one is
          ...
        ],
        "fee" : n,                           (numeric) difference in value between transaction inputs and outputs (in satoshis); for coinbase transactions, this is a negative Number of the total collected block fees (ie, not including the block subsidy); if key is not present, fee is unknown and clients MUST NOT assume there isn't one
        "sigops" : n,                        (numeric) total SigOps cost, as counted for purposes of block limits; if key is not present, sigop cost is unknown and clients MUST NOT assume it is zero
        "weight" : n                         (numeric) total transaction weight, as counted for purposes of block limits
      },
      ...
    ],
    "coinbaseaux" : {                        (json object) data that should be included in the coinbase's scriptSig content
      "key" : "hex",                         (string) values must be in the coinbase (keys may be ignored)
      ...
    },
    "coinbasevalue" : n,                     (numeric) maximum allowable input to coinbase transaction, including the generation award and transaction fees (in satoshis)
    "longpollid" : "str",                    (string) an id to include with a request to longpoll on an update to this template
    "target" : "str",                        (string) The hash target
    "mintime" : xxx,                         (numeric) The minimum timestamp appropriate for the next block time, expressed in UNIX epoch time
    "mutable" : [                            (json array) list of ways the block template may be changed
      "str",                                 (string) A way the block template may be changed, e.g. 'time', 'transactions', 'prevblock'
      ...
    ],
    "noncerange" : "hex",                    (string) A range of valid nonces
    "sigoplimit" : n,                        (numeric) limit of sigops in blocks
    "sizelimit" : n,                         (numeric) limit of block size
    "weightlimit" : n,                       (numeric, optional) limit of block weight
    "curtime" : xxx,                         (numeric) current timestamp in UNIX epoch time
    "bits" : "str",                          (string) compressed target of next block
    "height" : n,                            (numeric) The height of the next block
    "signet_challenge" : "hex",              (string, optional) Only on signet
    "default_witness_commitment" : "hex"     (string, optional) a valid witness commitment for the unmodified block template
  }