Automatic UTXO Selection

Automatic UTXO Selection in Testing Environments

Overview

When building a Cardano transaction with Anvil API, you have two options for specifying transaction inputs:

1. Provide UTXO List - Explicitly specify which UTXOs to use (required in production)

2. Automatic Selection - Let Anvil choose UTXOs for you (testing environments only)

Automatic UTXO Selection in Testing

In test environments (preprod, preview), the utxos parameter in the transaction building API is optional. If you don't provide it, Anvil will:

• Automatically fetch UTXOs associated with the changeAddress

• Select appropriate UTXOs to cover the transaction

• Handle all input management for you

This simplifies development and testing by removing the need to manage UTXO selection logic until you're ready for production.

// Example: Let Anvil handle UTXO selection (test environments only)
const response = await fetch('https://preprod.api.ada-anvil.app/v2/services/transactions/build', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Api-Key': 'YOUR_API_KEY'
  },
  body: JSON.stringify({
    // Just provide a change address - no UTXOs needed!
    changeAddress: 'addr_test...',
    outputs: [
      {
        address: 'recipient_address',
        lovelace: 5000000 // 5 ADA
      }
    ]
  })
});

Production Requirement

For production environments, you must explicitly provide UTXOs using the utxos parameter:

// Production example: Explicitly provide UTXOs
const response = await fetch('https://prod.api.ada-anvil.app/v2/services/transactions/build', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-Api-Key': 'YOUR_API_KEY'
  },
  body: JSON.stringify({
    changeAddress: 'addr...',
    // UTXO list is required in production
    utxos: ['8282...', '8282...'],
    outputs: [
      {
        address: 'recipient_address',
        lovelace: 5000000 // 5 ADA
      }
    ]
  })
});

Why Is This Useful?

Automatic UTXO selection simplifies development and testing by:

• Reducing implementation complexity during early development

• Allowing you to focus on application logic rather than UTXO management

• Making it faster to prototype and test functionality

Related Resources

• Transaction Building
• Utility Functions