This guide walks you through a complete swap flow from Bitcoin (BTC) to Ethereum USDC using the LeoKit API. We’ll cover all five steps: getting a quote, generating a deposit transaction, signing and broadcasting, saving the transaction hash, and tracking the swap status.
Overview
The complete swap flow consists of 5 steps:
- Get Quote - Request swap rates from multiple protocols
- Generate Deposit - Create an unsigned transaction
- Sign & Broadcast - Sign with wallet and broadcast to blockchain
- Save Transaction - Register the transaction hash with LeoKit
- Track Status - Monitor swap progress until completion
Example: BTC → ETH USDC
Let’s swap 1 BTC (100,000,000 satoshis) to USDC on Ethereum.
Step 1: Get Quote
Request quotes from all supported protocols to find the best rate.
curl -X GET 'https://api.leodex.io/leokit/quote?from_asset=BTC.BTC&to_asset=ETH.USDC-0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&amount=100000000&destination=0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb&origin=bc1qxy2kgdygjrsqtzq2n0yrf2493p83kkfjhx0wlh&slippage_bps=150' \
-H 'Api-Key: your_api_key_here'
{
"quotes": [
{
"protocol": "thorchain",
"data": {
"expected_amount_out": "9850000000",
"total_swap_seconds": 180,
"fees": [...],
"route": ["BTC.BTC", "THOR.RUNE", "ETH.USDC-0xA0b86991..."],
"flags": ["OPTIMAL", "CHEAPEST"]
}
}
],
"timestamp": "2026-01-15T12:34:56.789Z",
"quote_id": "01936b4a-7c8e-7890-abcd-ef1234567890"
}
Save the quote_id - you’ll need it for all subsequent steps. Quote IDs expire after 15 minutes.
Step 2: Generate Deposit Transaction
Create an unsigned transaction using the quote ID and your selected protocol.
curl -X POST 'https://api.leodex.io/leokit/deposit' \
-H 'Api-Key: your_api_key_here' \
-H 'Content-Type: application/json' \
-d '{
"quote_id": "01936b4a-7c8e-7890-abcd-ef1234567890",
"selected_protocol": "thorchain"
}'
{
"type": "UTXO",
"protocol": "thorchain",
"quote_id": "01936b4a-7c8e-7890-abcd-ef1234567890",
"details": {
"from_address": "bc1qxy2kgdygjrsqtzq2n0yrf2493p83kkfjhx0wlh",
"to_address": "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb",
"from_asset": "BTC.BTC",
"to_asset": "ETH.USDC-0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
"amount": "100000000",
"decimals": 8,
"memo": "=:ETH.USDC-0xA0b86991:0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb:985000000"
},
"unsigned_transaction": {
"psbt_hex": "cHNidP8BAH0CAAAAAR...",
"selected_utxos": [...],
"chain": "BTC"
}
}
For Bitcoin transactions, LeoKit returns a PSBT (Partially Signed Bitcoin Transaction) that you’ll sign in the next step.
Step 3: Sign & Broadcast (Client-Side)
Sign the transaction with your wallet and broadcast it to the Bitcoin network.
// Using bitcoinjs-lib
import * as bitcoin from "bitcoinjs-lib";
const psbt = bitcoin.Psbt.fromHex(depositData.unsigned_transaction.psbt_hex);
// Sign with wallet (example with private key)
psbt.signAllInputs(keyPair);
psbt.finalizeAllInputs();
const txHex = psbt.extractTransaction().toHex();
// Broadcast to Bitcoin network
const txHash = await broadcastBitcoinTransaction(txHex);
Never expose your private keys. This example is for educational purposes. Use secure wallet libraries in production.
Step 4: Save Transaction Hash
Register the transaction hash with LeoKit to enable status tracking.
curl -X POST 'https://api.leodex.io/leokit/save-transaction' \
-H 'Api-Key: your_api_key_here' \
-H 'Content-Type: application/json' \
-d '{
"quote_id": "01936b4a-7c8e-7890-abcd-ef1234567890",
"tx_hash": "a1b2c3d4e5f67890abcdef1234567890abcdef1234567890abcdef1234567890"
}'
Step 5: Track Status
Poll the status endpoint to monitor your swap progress.
curl -X POST 'https://api.leodex.io/leokit/status' \
-H 'Api-Key: your_api_key_here' \
-H 'Content-Type: application/json' \
-d '{
"quote_id": "01936b4a-7c8e-7890-abcd-ef1234567890"
}'
Status Values
| Status | Description |
|---|
pending | Transaction broadcasted, waiting for confirmation |
observed | Transaction confirmed on source chain |
inbound_observed | Protocol detected the deposit |
swap_in_progress | Cross-chain swap executing |
outbound_observed | Tokens being sent to destination |
completed | Swap successful, tokens received |
failed | Swap failed (reverted or error) |
Best Practices
Use appropriate polling intervals - Poll every 10-15 seconds. Faster polling won’t speed up the swap.
Save quote_id persistently - Store it in your database to track swaps even after page refreshes.
Handle timeouts gracefully - Cross-chain swaps can take 5-10 minutes. Show progress indicators to users.
Test with small amounts first - Always test new integrations with minimal amounts on testnet/mainnet.
Next Steps
