construction/metadata - Cardano

Example code for the construction/metadata JSON-RPC method. Complete guide on how to use construction/metadata JSON-RPC in GetBlock Web3 documentation.

This endpoint returns the online metadata needed to construct a transaction, such as the current fee parameters and time-to-live, from the options produced by preprocess.

Parameters

The request body is a JSON object with the following fields.

Field	Type	Required	Description
network_identifier	object	Yes	The network to construct for
options	object	Yes	The options returned by the preprocess endpoint
public_keys	array	No	Public keys required for the transaction

Request

cURL

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/construction/metadata' \
--header 'Content-Type: application/json' \
--data-raw '{
    "network_identifier": {
        "blockchain": "cardano",
        "network": "mainnet"
    },
    "options": {
        "relative_ttl": 1000,
        "transaction_size": 246
    }
}'

JavaScript

example.js

const response = await fetch(
    'https://go.getblock.io/<ACCESS-TOKEN>/construction/metadata',
    {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({"network_identifier": {"blockchain": "cardano", "network": "mainnet"}, "options": {"relative_ttl": 1000, "transaction_size": 246}})
    }
);
console.log(await response.json());

Python

example.py

import requests

response = requests.post(
    'https://go.getblock.io/<ACCESS-TOKEN>/construction/metadata',
    headers={'Content-Type': 'application/json'},
    json={"network_identifier": {"blockchain": "cardano", "network": "mainnet"}, "options": {"relative_ttl": 1000, "transaction_size": 246}}
)

print(response.json())

Response

{
    "metadata": {
        "ttl": 193929071,
        "protocol_parameters": {
            "coinsPerUtxoSize": "4310",
            "maxTxSize": 16384,
            "maxValSize": 5000,
            "keyDeposit": "2000000",
            "maxCollateralInputs": 3,
            "minFeeCoefficient": 44,
            "minFeeConstant": 155381,
            "minPoolCost": "170000000",
            "poolDeposit": "500000000",
            "protocol": 11
        }
    },
    "suggested_fee": [
        {
            "value": "166205",
            "currency": {
                "symbol": "ADA",
                "decimals": 6
            }
        }
    ]
}

Response Parameters

Field	Type	Description
metadata	object	Metadata required to build the transaction, such as ttl
suggested_fee	array	The suggested fee for the transaction, in ada

Use Cases

• Fee Fetching: Read the suggested fee before building payloads

• TTL Resolution: Resolve the absolute time to live from relative options

• Online Step: Fetch chain-dependent metadata for construction

• Transaction Building: Feed metadata into the payloads endpoint

Error Handling

Error Code	Message	Description
1	Invalid request	A required construction field is missing or malformed
6	Transaction decode failed	The supplied transaction could not be decoded
14	Invalid signature	A supplied signature is malformed or does not match
5	Internal error	The node failed to process the construction step