POST /rpc

POST

https://casper.nownodes.io/rpc

Authorizations

ApiKeyAuthApiKeyAuth

api-key string

NOWNodes API key passed in the api-key header.

Executes a Version1 transaction locally without committing it to the blockchain. Returns the execution result.

Body

application/json

JSON-RPC request

jsonrpcstringrequired

JSON-RPC protocol version

methodstringrequired

RPC method

paramsobjectrequired

Transaction object to execute speculatively

Show child attributes

transactionobject

Show child attributes

Version1object

Version1 transaction

Show child attributes

headerobject

Metadata for the transaction

Show child attributes

chain_namestring

timestampstring<date-time>

ttlstring

body_hashstring

pricing_modeobject

Show child attributes

Fixedobject

Show child attributes

gas_price_toleranceinteger

payloadobject

Transaction fields and arguments

Show child attributes

fieldsobject

Show child attributes

initiator_addrobject

Show child attributes

PublicKeystring

argsArray<Array<object>>

Arguments for the transaction

targetstring

entry_pointstring

transaction_categoryinteger

schedulingstring

approvalsArray<object>

List of approvals (can be empty for speculative execution)

Show child attributes

signerstring

signaturestring

Response

200OK

Speculative execution result

POST /rpc

curl -X POST 'https://casper.nownodes.io/rpc' \
  -H 'Content-Type: application/json' \
  -d '{
    "jsonrpc": "2.0",
    "method": "speculative_exec_txn",
    "params": {
      "transaction": {
        "Version1": {
          "header": {
            "chain_name": "casper",
            "timestamp": "2025-12-10T12:00:00.000Z",
            "ttl": "1h",
            "body_hash": "PLACEHOLDER_BODY_HASH",
            "pricing_mode": {
              "Fixed": {
                "gas_price_tolerance": 1
              }
            }
          },
          "payload": {
            "fields": {
              "initiator_addr": {
                "PublicKey": "01abcdef...123456"
              },
              "args": [
                [
                  {}
                ]
              ],
              "target": "Native",
              "entry_point": "Transfer",
              "transaction_category": 0,
              "scheduling": "Standard"
            }
          },
          "approvals": [
            {
              "signer": "string",
              "signature": "string"
            }
          ]
        }
      }
    }
  }'

import { JsonRpcProvider } from "ethers";

const provider = new JsonRpcProvider("https://casper.nownodes.io/rpc");
const result = await provider.send("speculative_exec_txn", {
  "transaction": {
    "Version1": {
      "header": {
        "chain_name": "casper",
        "timestamp": "2025-12-10T12:00:00.000Z",
        "ttl": "1h",
        "body_hash": "PLACEHOLDER_BODY_HASH",
        "pricing_mode": {
          "Fixed": {
            "gas_price_tolerance": 1
          }
        }
      },
      "payload": {
        "fields": {
          "initiator_addr": {
            "PublicKey": "01abcdef...123456"
          },
          "args": [
            [
              {}
            ]
          ],
          "target": "Native",
          "entry_point": "Transfer",
          "transaction_category": 0,
          "scheduling": "Standard"
        }
      },
      "approvals": [
        {
          "signer": "string",
          "signature": "string"
        }
      ]
    }
  }
});
console.log(result);

require 'eth'
require 'json'
require 'net/http'

uri = URI('https://casper.nownodes.io/rpc')
request = Net::HTTP::Post.new(uri)
request['Content-Type'] = 'application/json'
request.body = '{
  "jsonrpc": "2.0",
  "method": "speculative_exec_txn",
  "params": {
    "transaction": {
      "Version1": {
        "header": {
          "chain_name": "casper",
          "timestamp": "2025-12-10T12:00:00.000Z",
          "ttl": "1h",
          "body_hash": "PLACEHOLDER_BODY_HASH",
          "pricing_mode": {
            "Fixed": {
              "gas_price_tolerance": 1
            }
          }
        },
        "payload": {
          "fields": {
            "initiator_addr": {
              "PublicKey": "01abcdef...123456"
            },
            "args": [
              [
                {}
              ]
            ],
            "target": "Native",
            "entry_point": "Transfer",
            "transaction_category": 0,
            "scheduling": "Standard"
          }
        },
        "approvals": [
          {
            "signer": "string",
            "signature": "string"
          }
        ]
      }
    }
  },
  "id": 1
}'

response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
  http.request(request)
end

puts JSON.parse(response.body)

from web3 import Web3

w3 = Web3(Web3.HTTPProvider("https://casper.nownodes.io/rpc"))
response = w3.provider.make_request("speculative_exec_txn", {
  "transaction": {
    "Version1": {
      "header": {
        "chain_name": "casper",
        "timestamp": "2025-12-10T12:00:00.000Z",
        "ttl": "1h",
        "body_hash": "PLACEHOLDER_BODY_HASH",
        "pricing_mode": {
          "Fixed": {
            "gas_price_tolerance": 1
          }
        }
      },
      "payload": {
        "fields": {
          "initiator_addr": {
            "PublicKey": "01abcdef...123456"
          },
          "args": [
            [
              {}
            ]
          ],
          "target": "Native",
          "entry_point": "Transfer",
          "transaction_category": 0,
          "scheduling": "Standard"
        }
      },
      "approvals": [
        {
          "signer": "string",
          "signature": "string"
        }
      ]
    }
  }
})
print(response)

import { createPublicClient, http } from "viem";

const client = createPublicClient({
  transport: http("https://casper.nownodes.io/rpc"),
});

const result = await client.request({
  method: "speculative_exec_txn",
  params: {
  "transaction": {
    "Version1": {
      "header": {
        "chain_name": "casper",
        "timestamp": "2025-12-10T12:00:00.000Z",
        "ttl": "1h",
        "body_hash": "PLACEHOLDER_BODY_HASH",
        "pricing_mode": {
          "Fixed": {
            "gas_price_tolerance": 1
          }
        }
      },
      "payload": {
        "fields": {
          "initiator_addr": {
            "PublicKey": "01abcdef...123456"
          },
          "args": [
            [
              {}
            ]
          ],
          "target": "Native",
          "entry_point": "Transfer",
          "transaction_category": 0,
          "scheduling": "Standard"
        }
      },
      "approvals": [
        {
          "signer": "string",
          "signature": "string"
        }
      ]
    }
  }
},
});

console.log(result);

const endpoint = "https://casper.nownodes.io/rpc";
const apiKey = "YOUR_API_KEY";

async function nownodesRequest(payload) {
  const response = await fetch(endpoint, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "api-key": apiKey,
    },
    body: JSON.stringify(payload),
  });

  return response.json();
}

const result = await nownodesRequest({ jsonrpc: "2.0", method: "speculative_exec_txn", params: {
  "transaction": {
    "Version1": {
      "header": {
        "chain_name": "casper",
        "timestamp": "2025-12-10T12:00:00.000Z",
        "ttl": "1h",
        "body_hash": "PLACEHOLDER_BODY_HASH",
        "pricing_mode": {
          "Fixed": {
            "gas_price_tolerance": 1
          }
        }
      },
      "payload": {
        "fields": {
          "initiator_addr": {
            "PublicKey": "01abcdef...123456"
          },
          "args": [
            [
              {}
            ]
          ],
          "target": "Native",
          "entry_point": "Transfer",
          "transaction_category": 0,
          "scheduling": "Standard"
        }
      },
      "approvals": [
        {
          "signer": "string",
          "signature": "string"
        }
      ]
    }
  }
}, id: 1 });
console.log(result);

const response = await fetch('https://casper.nownodes.io/rpc', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
      "jsonrpc": "2.0",
      "method": "speculative_exec_txn",
      "params": {
        "transaction": {
          "Version1": {
            "header": {
              "chain_name": "casper",
              "timestamp": "2025-12-10T12:00:00.000Z",
              "ttl": "1h",
              "body_hash": "PLACEHOLDER_BODY_HASH",
              "pricing_mode": {
                "Fixed": {
                  "gas_price_tolerance": 1
                }
              }
            },
            "payload": {
              "fields": {
                "initiator_addr": {
                  "PublicKey": "01abcdef...123456"
                },
                "args": [
                  [
                    {}
                  ]
                ],
                "target": "Native",
                "entry_point": "Transfer",
                "transaction_category": 0,
                "scheduling": "Standard"
              }
            },
            "approvals": [
              {
                "signer": "string",
                "signature": "string"
              }
            ]
          }
        }
      }
    }),
});

const data = await response.json();

import requests

payload = {
  "jsonrpc": "2.0",
  "method": "speculative_exec_txn",
  "params": {
    "transaction": {
      "Version1": {
        "header": {
          "chain_name": "casper",
          "timestamp": "2025-12-10T12:00:00.000Z",
          "ttl": "1h",
          "body_hash": "PLACEHOLDER_BODY_HASH",
          "pricing_mode": {
            "Fixed": {
              "gas_price_tolerance": 1
            }
          }
        },
        "payload": {
          "fields": {
            "initiator_addr": {
              "PublicKey": "01abcdef...123456"
            },
            "args": [
              [
                {}
              ]
            ],
            "target": "Native",
            "entry_point": "Transfer",
            "transaction_category": 0,
            "scheduling": "Standard"
          }
        },
        "approvals": [
          {
            "signer": "string",
            "signature": "string"
          }
        ]
      }
    }
  }
}

response = requests.post('https://casper.nownodes.io/rpc', json=payload)
data = response.json()

require 'net/http'
require 'json'

uri = URI('https://casper.nownodes.io/rpc')
request = Net::HTTP::Post.new(uri)
request['Content-Type'] = 'application/json'
request.body = '{
    "jsonrpc": "2.0",
    "method": "speculative_exec_txn",
    "params": {
      "transaction": {
        "Version1": {
          "header": {
            "chain_name": "casper",
            "timestamp": "2025-12-10T12:00:00.000Z",
            "ttl": "1h",
            "body_hash": "PLACEHOLDER_BODY_HASH",
            "pricing_mode": {
              "Fixed": {
                "gas_price_tolerance": 1
              }
            }
          },
          "payload": {
            "fields": {
              "initiator_addr": {
                "PublicKey": "01abcdef...123456"
              },
              "args": [
                [
                  {}
                ]
              ],
              "target": "Native",
              "entry_point": "Transfer",
              "transaction_category": 0,
              "scheduling": "Standard"
            }
          },
          "approvals": [
            {
              "signer": "string",
              "signature": "string"
            }
          ]
        }
      }
    }
  }'

response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |http| http.request(request) }
data = JSON.parse(response.body)

Request Body

{
  "jsonrpc": "2.0",
  "method": "speculative_exec_txn",
  "params": {
    "transaction": {
      "Version1": {
        "header": {
          "chain_name": "casper",
          "timestamp": "2025-12-10T12:00:00.000Z",
          "ttl": "1h",
          "body_hash": "PLACEHOLDER_BODY_HASH",
          "pricing_mode": {
            "Fixed": {
              "gas_price_tolerance": 1
            }
          }
        },
        "payload": {
          "fields": {
            "initiator_addr": {
              "PublicKey": "01abcdef...123456"
            },
            "args": [
              [
                {}
              ]
            ],
            "target": "Native",
            "entry_point": "Transfer",
            "transaction_category": 0,
            "scheduling": "Standard"
          }
        },
        "approvals": [
          {
            "signer": "string",
            "signature": "string"
          }
        ]
      }
    }
  }
}

200

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "api_version": "2.0.0",
    "execution_result": {
      "success": true,
      "effect": {},
      "cost": "1000000"
    }
  }
}

Documentation

How to migrate to NOWNodes

Authorizations

Body

Response