Client API

The Client API exposes Hydra App's ClientService — on-chain transaction creation, signing, and broadcasting for native assets, tokens, fee bumps, and token allowances.

JSON-RPC namespace: client

The service exposes two parallel flows:

• Build → sign → finalize — Create*Transaction returns an unsigned TransactionRequest. Sign it with signer.SignTransaction, then submit with FinalizeAndBroadcastTransaction. Use this when you want to inspect the transaction or use an external signer.
• One-shot send — SendTransaction, SendTokenTransaction, BumpTransaction, SetTokenAllowance build, sign, and broadcast in a single call.

Looking for GetDepositAddress? That moved to the Wallet API.

Endpoints

Build → sign → finalize

• Create Send Transaction
• Create Bump Transaction
• Create Token Send Transaction
• Create Set Token Allowance Transaction
• Finalize And Broadcast Transaction

One-shot

• Send Transaction
• Send Token Transaction
• Bump Transaction
• Set Token Allowance

Token permits (2026-09-11)

• Estimate Token Permit Fee
• Create Token Permit Transaction
• Submit Token Permit

Create Send Transaction

Builds an unsigned native asset send transaction. Returns a generic TransactionRequest that can be inspected, signed via signer.SignTransaction, and then submitted via FinalizeAndBroadcastTransaction.

Method: CreateSendTransaction

Parameters:

Response:

Example Request:

import { CreateSendTransactionRequest } from './proto/client_pb'

const request = new CreateSendTransactionRequest()
request.setNetwork({ protocol: 1, id: '0a03cf40' })
request.setTo('bc1qrecipient...')
request.setAmount({ exact: { amount: { value: '0.01' } } })
request.setFeeOption({ /* see Fee API for options */ })

const response = await client.createSendTransaction(request, {})
const txRequest = response.getTransactionRequest()
// → pass txRequest to signer.SignTransaction

Create Bump Transaction

Builds an unsigned fee-bump (RBF / speed-up) transaction request for an existing unconfirmed transaction.

Method: CreateBumpTransaction

Parameters:

Response:

Example Request:

import { CreateBumpTransactionRequest } from './proto/client_pb'

const request = new CreateBumpTransactionRequest()
request.setNetwork({ protocol: 1, id: '0a03cf40' })
request.setTxid('abc123...')
request.setFeeOption({ /* higher fee */ })

const response = await client.createBumpTransaction(request, {})
const txRequest = response.getTransactionRequest()

Create Token Send Transaction

Builds an unsigned ERC-20 / token transfer transaction. For native asset transfers use Create Send Transaction.

Method: CreateTokenSendTransaction

Parameters:

Response:

Example Request:

import { CreateTokenSendTransactionRequest } from './proto/client_pb'

const request = new CreateTokenSendTransactionRequest()
request.setNetwork({ protocol: 2, id: '11155111' })
request.setTo('0xrecipient...')
request.setTokenId('0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48') // USDC
request.setAmount({ exact: { amount: { value: '100' } } })
request.setFeeOption({ /* ... */ })

const response = await client.createTokenSendTransaction(request, {})
const txRequest = response.getTransactionRequest()

Create Set Token Allowance Transaction

Builds an unsigned token allowance approval transaction. Supports ERC-20, ERC-721, and ERC-1155.

Method: CreateSetTokenAllowanceTransaction

Parameters:

Response:

Example Request:

import { CreateSetTokenAllowanceTransactionRequest } from './proto/client_pb'

const request = new CreateSetTokenAllowanceTransactionRequest()
request.setNetwork({ protocol: 2, id: '11155111' })
request.setSpender('0xspender...')
request.setAllowance({ /* SetTokenAllowance */ })
request.setFeeOption({ /* ... */ })

const response = await client.createSetTokenAllowanceTransaction(request, {})
const txRequest = response.getTransactionRequest()

Finalize And Broadcast Transaction

Submits a signed transaction to the network. Accepts a SignedTransactionRequest (as returned by signer.SignTransaction) and returns the resulting transaction ID.

Method: FinalizeAndBroadcastTransaction

Parameters:

Response:

Example Request:

import { FinalizeAndBroadcastTransactionRequest } from './proto/client_pb'

// signedTx is the SignedTransactionRequest returned by signer.SignTransaction
const request = new FinalizeAndBroadcastTransactionRequest()
request.setNetwork({ protocol: 1, id: '0a03cf40' })
request.setSignedTx(signedTx)

const response = await client.finalizeAndBroadcastTransaction(request, {})
console.log('Broadcast TXID:', response.getTxid())

Example Response:

{ "txid": "abc123def456..." }

Send Transaction

Send the native asset of a network to another address. Builds, signs and broadcasts in one call.

Method: SendTransaction

Parameters:

Amount

Amount is a oneof, not a struct with a value. Exactly one arm is set, and it carries no asset id — the asset is the network's native one for SendTransaction, and token_id for SendTokenTransaction.

FeeOption

FeeOption is also a oneof message, not an enum. Three arms select a network estimate; the fourth carries an explicit rate.

There is no FeeOption.MEDIUM constant. Older revisions of this page showed FeeOption as an enum with LOW / MEDIUM / HIGH / CUSTOM values and Amount as { value, asset_id }. Neither has ever existed in the proto — see Fee structures for the real shapes.

Response:

Example Request:

import { SendTransactionRequest } from './proto/client_pb'

const request = new SendTransactionRequest()
request.setNetwork({ protocol: 1, id: '0a03cf40' })
request.setTo('tb1q...')
request.setAmount({ exact: { amount: { value: '0.001' } } })
request.setFeeOption({ medium: {} })

const response = await client.sendTransaction(request, {})
console.log('Transaction ID:', response.getTxid())

Example Response:

{ "txid": "abc123..." }

Send Token Transaction

Send a token (non-native asset) to another address. For native transfers use Send Transaction.

Method: SendTokenTransaction

Parameters:

Response:

Example Request:

// Send 100 USDC on Ethereum Sepolia
const request = new SendTokenTransactionRequest()
request.setNetwork({ protocol: 2, id: '11155111' })
request.setTo('0xrecipient...')
request.setTokenId('erc20:0x8cd0da3d001b013336918b8bc4e56d9dda1347e0')
request.setAmount({ exact: { amount: { value: '100' } } })
request.setFeeOption({ medium: {} })

const response = await client.sendTokenTransaction(request, {})

Example Response:

{ "txid": "0x..." }

The token must be registered on the node — listed under the network's tokens in config.yaml, or added at runtime with asset.AddToken. An unregistered token_id is rejected.

Bump Transaction

Increase the fee of an existing unconfirmed transaction to speed up confirmation (RBF on Bitcoin, a same-nonce replacement on EVM).

Method: BumpTransaction

Parameters:

Response:

Example Request:

const request = new BumpTransactionRequest()
request.setNetwork({ protocol: 1, id: '0a03cf40' })
request.setTxid('abc123...')
request.setFeeOption({ high: {} })

const response = await client.bumpTransaction(request, {})

Example Response:

{ "txid": "def456..." }

Set Token Allowance

Approve a spender to move tokens on the wallet's behalf. Builds, signs and broadcasts in one call.

Method: SetTokenAllowance

Parameters:

SetTokenAllowance

A oneof over the three approval shapes the token standards use:

AllowanceAmount is itself a oneof: unlimited (empty) or exact { amount: DecimalString }.

Response:

Example Request:

const request = new SetTokenAllowanceRequest()
request.setNetwork({ protocol: 2, id: '11155111' })
request.setSpender('0xspender...')
request.setAllowance({
  token: {
    token_id: 'erc20:0x8cd0da3d001b013336918b8bc4e56d9dda1347e0',
    amount: { exact: { amount: { value: '1000' } } },
  },
})
request.setFeeOption({ medium: {} })

const response = await client.setTokenAllowance(request, {})

Example Response:

{ "txid": "0x..." }

Read the current state back with blockchain.GetTokenAllowance.

Token permits

Added 2026-09-11.

A token permit is an allowance its owner authorises with an off-chain signature instead of an on-chain approve. Whoever submits the permit pays the gas — so a wallet that holds a token but no native asset can still grant an allowance, as long as someone else sends the transaction.

The three RPCs below are the submitting side: this wallet sends a permit that some owner signed, and pays for it. owner and this wallet are usually different parties.

The flow:

1. Read the token's terms with blockchain.GetTokenPermitTerms. No terms ⇒ the token offers no signature-authorised allowance to that owner, and the permit path is unavailable — fall back to SetTokenAllowance.
2. Price the submission with EstimateTokenPermitFee. The permit does not exist yet — the owner signs once the price is known.
3. The owner signs the terms, producing a TokenPermit.
4. Submit it with SubmitTokenPermit, or build it unsigned with CreateTokenPermitTransaction for an external signer.

TokenPermit

⚠️ TokenPermit.value is the one amount that is not in whole units

It is a U256String in the token's smallest unit — the value that goes on the wire to the contract — because that is what the owner's signature commits to, and re-deriving it from a decimal would risk signing for a different number. Everywhere else in this API an amount is a whole-unit DecimalString; EstimateTokenPermitFee.value below is one of those.

Estimate Token Permit Fee

What submitting a permit would cost this wallet, priced against the owner's live allowance and permit nonce on the token. Nothing is signed or sent.

Method: EstimateTokenPermitFee

Parameters:

Response:

Call this before the owner signs. Pricing needs the owner's live state on the token — an allowance already at the target value, or a different permit nonce, changes what the submission costs — which is exactly why it takes no signature.

Create Token Permit Transaction

Builds the unsigned transaction that submits a signed permit, for inspection or an external signer. The permit's owner authorised the allowance off-chain; this wallet sends the transaction and pays the fee.

Method: CreateTokenPermitTransaction

Parameters:

Response:

Submit Token Permit

Creates, signs and broadcasts the transaction that sets the allowance the permit's owner authorised.

Method: SubmitTokenPermit

Parameters:

Response:

Example Request:

import { SubmitTokenPermitRequest } from './proto/client_pb'

const request = new SubmitTokenPermitRequest()
request.setNetwork({ protocol: 2, id: '11155111' })
request.setPermit({
  token_id: 'erc20:0x8cd0da3d001b013336918b8bc4e56d9dda1347e0',
  owner: '0xowner...',
  spender: '0xspender...',
  value: { value: '1000000000' },          // smallest unit
  deadline: Math.floor(Date.now() / 1000) + 3600,
  terms: termsBytes,                        // from blockchain.GetTokenPermitTerms
  signature: signatureBytes,                // the owner's signature over those terms
})
request.setFeeOption({ medium: {} })

const response = await client.submitTokenPermit(request, {})
console.log('permit submitted:', response.getTxid())

Example Response:

{ "txid": "0x..." }

A permit whose deadline has passed, whose signature does not match owner, or whose nonce the token has already consumed is rejected by the token contract — the transaction reverts and the fee is still spent. Submit promptly after signing, and re-read the terms if a submission fails.

The same rail is what the liquidity service uses to fund a channel for a wallet that holds the token but no gas — see SponsoredDepositFeePayment and the swap DepositRail in Swap API.

Network ID Formats

Different networks use different ID formats:

Bitcoin Networks

• Mainnet: f9beb4d9
• Testnet4: 1c163f28
• Testnet3: 0b110907
• Signet: 0a03cf40
• Regtest: fabfb5da

EVM Networks

• Ethereum Mainnet: 1
• Ethereum Sepolia: 11155111
• Arbitrum One: 42161
• Arbitrum Sepolia: 421614
• Optimism: 10
• Polygon: 137

Common Patterns

Build → sign → broadcast with an external signer

// 1. Build the unsigned transaction.
const build = new CreateSendTransactionRequest()
build.setNetwork({ protocol: 1, id: '0a03cf40' })
build.setTo('tb1q...')
build.setAmount({ exact: { amount: { value: '0.001' } } })
build.setFeeOption({ medium: {} })

const txRequest = (await client.createSendTransaction(build, {})).getTransactionRequest()

// 2. `signable_data` is the wallet-standard payload for the network:
//    EVM → UTF-8 JSON eth_sendTransaction params; Bitcoin → base64 BIP-174 PSBT.
//    Hand it to signer.SignTransaction, or to your own signer.
const signed = await signerClient.signTransaction(/* … txRequest … */)

// 3. Finalize + broadcast.
const fin = new FinalizeAndBroadcastTransactionRequest()
fin.setNetwork({ protocol: 1, id: '0a03cf40' })
fin.setSignedTx(signed)

console.log('txid:', (await client.finalizeAndBroadcastTransaction(fin, {})).getTxid())

TransactionRequest carries the estimate too — fee_units (gas for EVM, weight units for Bitcoin) and an optional fee. Check them before signing; the one-shot Send* calls give you no such window.

Deposit addresses

Deposit addresses are on the Wallet API, not here — wallet.GetDepositAddress for the wallet's standing address, wallet.GetUniqueDepositAddress for a fresh one per invoice on Bitcoin.

Error Handling

Best Practices

1. Validate addresses before sending. An on-chain send is irreversible; the API does not second-guess a well-formed address.
2. Check the balance first — wallet.GetBalance. The native asset also has to cover the fee, which is a separate resource from the token you are moving.
3. Pick the fee by urgency — low when you can wait, high when you cannot, custom when you have your own estimate.
4. Prefer build → sign → finalize when the amount is large. It is the only flow that lets you inspect fee_units and fee before committing.
5. Follow the transaction afterwards — wallet.GetTransaction, or the TransactionUpdate on SubscribeClientEvents.
6. Bump rather than resend. A second send is a second transaction; BumpTransaction replaces the first.

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