Build a testnet app

Why build on testnet first #

Testnet runs the same protocol as mainnet with coins that are worth nothing. That makes it the right place to write and debug an integration: you can fund an address for free from the faucet, send real transactions, and get everything wrong without losing a cent.

Two ways to reach a chain #

An app needs a way to read the chain and push transactions to it. You have two options, and many apps use both:

• Run your own node and talk to it over RPC. Full control and no third party, but you run the infrastructure.
• Use an explorer API over HTTP. No infrastructure to run, and it works straight from a browser.

Path A: your own node #

Set one up with run a Litecoin testnet node (the same pattern works for Bitcoin), then drive it over RPC:

litecoin-cli -testnet getblockchaininfo      # is it synced?
litecoin-cli -testnet getnewaddress          # an address to fund
litecoin-cli -testnet listunspent            # your spendable UTXOs
litecoin-cli -testnet gettransaction <txid>   # a wallet tx + its confirmations

The RPC interface can move funds, so keep it private. Read use node RPC safely before you expose anything.

Path B: an explorer API #

If you would rather not run a node, TestnetScan exposes a public, CORS-enabled HTTP API that is compatible with the mempool.space and Esplora conventions. The base is https://testnetscan.com/{net}/api/, where {net} is btc-testnet4 or ltc-testnet. A few examples you can run right now:

# current block height (plain number)
curl https://testnetscan.com/btc-testnet4/api/blocks/tip/height

# suggested fee rates (sat/vB, by target in blocks)
curl https://testnetscan.com/btc-testnet4/api/fee-estimates

# mempool summary
curl https://testnetscan.com/btc-testnet4/api/mempool

Address history, UTXOs, and transaction lookups follow the same Esplora-style paths (for example /api/address/<addr> and /api/tx/<txid>). Because the API answers with Access-Control-Allow-Origin: *, you can call it directly from front-end JavaScript. See the full reference in TestnetScan's API docs.

Build and broadcast #

Building a transaction means selecting UTXOs, adding outputs, setting a fee, and signing. Do it with a library in your language (for example a Bitcoin or Litecoin transaction-builder package) or let a wallet handle it. Then push the signed hex, either through your node or an explorer:

# via your node
litecoin-cli -testnet sendrawtransaction <signed-hex>

# or via the explorer (POST the raw hex)
curl -X POST --data <signed-hex> https://testnetscan.com/ltc-testnet/api/tx

The full walkthrough, including how to inspect a transaction before you send it and what the common rejection errors mean, is in broadcast a raw transaction.

Watch it confirm #

After broadcasting, poll until the transaction has enough confirmations for your use case. Ask the explorer for the transaction's status, or your node with gettransaction <txid>, which reports a live confirmation count for your wallet's transactions. If it never appears, see debugging a stuck transaction.

The whole loop #

Before you go to mainnet #

The code you write on testnet is the code you will run on mainnet, so build the safe habits now:

• Never reuse a testnet seed or key on mainnet. Generate fresh keys for real funds.
• Keep node RPC private. An exposed wallet RPC has drained real money.
• Wait for enough confirmations before treating a payment as final, and handle reorgs.
• Estimate fees from live data, and have a plan for stuck transactions (RBF or CPFP).