Accessing and processing information stored on the blockchain

Koios provides a query layer which allows your app to access information stored on the blockchain.

Get started:

There are 4 network that Koios provides:

const koiosProvider = new KoiosProvider('preprod', '<token>');

Get your token from Koios, by connecting your wallet and select a tier of your choice.

If you are using a privately hosted instance, you can set the URL in the parameter:

const koiosProvider = new KoiosProvider('<KOIOS_URL>');


Fetch account infomation

await koiosProvider.fetchAccountInfo(


Fetch UTXOs in the provided address. Optionally, you can filter UTXOs containing a particular asset by providing asset, where it is the concatenation of policy ID and asset.

await koiosProvider.fetchAddressUTxOs(


Fetch a list of a addresses containing a specific asset where it is the concatenation of policy ID and asset.

await koiosProvider.fetchAssetAddresses(


Fetch the asset metadata by providing asset's unit, which is the concatenation of policy ID and asset name in hex.

await koiosProvider.fetchAssetMetadata(


Fetch block infomation. You can get the hash from fetchTxInfo().

await koiosProvider.fetchBlockInfo(


Fetch a list of assets belonging to a collection by providing its Policy ID.

await koiosProvider.fetchCollectionAssets(
  'd9312da562da182b02322fd8acb536f37eb9d29fba7c49dc17255527', ,

The API will return a list of assets and a cursor next. If the cursor is not null, you can use it to fetch the next page of results. Here is an example of the response.

  "assets": [
      "unit": "d9312da562da182b02322fd8acb536f37eb9d29fba7c49dc172555274d657368546f6b656e",
      "quantity": "1"
  "next": null


ADA Handle allows users to use a human-readable "Handle" to associate an address.

Each Handle is a unique NFT, minted and issued on the Cardano blockchain. These NFTs act as unique identifiers for the UTXO that they reside in.

Working together with koiosProvider, we can resolve the handle's address with this API.

await koiosProvider.fetchHandleAddress(

Note: if you get an error here, you could be on the wrong network. Change the provider's network at the top of the page.


Fetch the latest protocol parameters. Optionally, you can provide an epoch number to fetch the protocol parameters of that epoch.

await koiosProvider.fetchProtocolParameters()


Fetch transaction infomation. Only confirmed transaction can be retrieved.

await koiosProvider.fetchTxInfo(


Submit a serialized transaction to the network.

await koiosProvider.submitTx(signedTx)


Allow you to listen to a transaction confirmation. Upon confirmation, the callback will be called.

const tx = new Transaction({ initiator: wallet });
tx.sendLovelace('addr_test1vpvx0sacufuypa2k4sngk7q40zc5c4npl337uusdh64kv0c7e4cxr', '5000000');

const unsignedTx = await tx.build();
const signedTx = await wallet.signTx(unsignedTx);
const txHash = await wallet.submitTx(signedTx);

koiosProvider.onTxConfirmed(txHash, () => {
  console.log('Transaction confirmed');