API Reference

Complete reference for the SmoothSend SDK classes and methods

SmoothSendTransactionSubmitter

Drop-in transaction submitter for the Aptos Wallet Adapter. Handles any transaction type — transfers, contract calls, NFT mints, DeFi. Credits deducted on mainnet.

Constructor

TypeScript

new SmoothSendTransactionSubmitter({
  apiKey: string,              // Required — your pk_nogas_* or sk_nogas_* key
  network?: string,            // 'testnet' | 'mainnet'  (default: 'testnet')
  gatewayUrl?: string,         // Override gateway URL   (default: https://proxy.smoothsend.xyz)
  timeout?: number,            // Request timeout ms     (default: 30000)
  debug?: boolean,             // Log requests/responses (default: false)
  getCaptchaToken?: () => Promise<string | null>,
                               // CAPTCHA callback — see Sponsorship Rules
})

Methods

submitTransaction(args)

Submits a signed transaction through the SmoothSend relayer. Implements the standard TransactionSubmitter interface from @aptos-labs/ts-sdk — no code changes needed in your existing wallet calls.

getSponsoredFunctions(): Promise<string[]>

Fetches the list of sponsored function identifiers from your project's Sponsorship Rules. Results are cached in memory — safe to call on every render. Used internally by useSmoothSend.

isSponsored(functionName: string): Promise<boolean>

Returns true if the given function identifier (e.g. 0x1::module::function) is in the project's sponsored allowlist. Calls getSponsoredFunctions() internally.

Usage

App.tsx

TypeScript

1import { SmoothSendTransactionSubmitter } from '@smoothsend/sdk';
2import { AptosWalletAdapterProvider } from '@aptos-labs/wallet-adapter-react';
3import { Network } from '@aptos-labs/ts-sdk';
4 
5const submitter = new SmoothSendTransactionSubmitter({
6  apiKey: process.env.NEXT_PUBLIC_SMOOTHSEND_API_KEY!,
7  network: 'mainnet',
8});
9 
10// Pass to provider — all wallet transactions are now gasless
11export function Providers({ children }: { children: React.ReactNode }) {
12  return (
13    <AptosWalletAdapterProvider
14      dappConfig={{ network: Network.MAINNET, transactionSubmitter: submitter }}
15    >
16      {children}
17    </AptosWalletAdapterProvider>
18  );
19}

useSmoothSend

React hook for automatic per-function gasless routing. Replaces useWallet().signAndSubmitTransaction and routes each call based on your Sponsorship Rules allowlist: sponsored → fee-payer gasless, not sponsored → user pays gas normally.

Signature

TypeScript

import { useSmoothSend } from '@smoothsend/sdk';
 
const { signAndSubmitTransaction } = useSmoothSend(submitter);

Parameters

submitter: SmoothSendTransactionSubmitter

A SmoothSendTransactionSubmitter instance. Create it once at module scope (not inside the component) to avoid recreating on every render.

Returns

signAndSubmitTransaction(input)

Same call signature as the wallet adapter's signAndSubmitTransaction. Automatically routes: sponsored functions use fee-payer gasless path; others fall back to the user paying gas via their wallet.

Usage

TodoList.tsx

TypeScript

1import { useSmoothSend, SmoothSendTransactionSubmitter } from '@smoothsend/sdk';
2import { useWallet } from '@aptos-labs/wallet-adapter-react';
3 
4// Create once at module scope
5const submitter = new SmoothSendTransactionSubmitter({
6  apiKey: process.env.NEXT_PUBLIC_SMOOTHSEND_API_KEY!,
7  network: 'mainnet',
8});
9 
10function TodoList() {
11  const { account } = useWallet();
12 
13  // Drop-in for useWallet().signAndSubmitTransaction
14  const { signAndSubmitTransaction } = useSmoothSend(submitter);
15 
16  const handleDelete = async (id: number) => {
17    // 'delete_todo' in sponsorship rules → gasless
18    // 'create_todo' not in rules → user pays gas
19    const result = await signAndSubmitTransaction({
20      data: {
21        function: `${MODULE_ADDRESS}::todolist::delete_todo`,
22        functionArguments: [id],
23      },
24    });
25    console.log('Tx hash:', result.hash);
26  };
27}

Note

The wallet must support signTransaction (sign-only) for the gasless path — Petra and Nightly both support this. If the wallet does not support it, the hook automatically falls back to user-pays-gas.

ScriptComposerClient

Builds fee-in-token transfers for mainnet stablecoins. No credits required — the relayer fee is deducted directly from the token being sent.

Constructor

TypeScript

new ScriptComposerClient({
  apiKey: string,
  network?: 'testnet' | 'mainnet', // default: 'testnet'
  gatewayUrl?: string,
  timeout?: number,
  debug?: boolean,
})

Methods

buildTransfer(params)

Builds a Script Composer transfer. Returns transactionBytes and a feeBreakdown — show the fee to users before they sign.

submitSignedTransaction(params)

Submits the signed transaction. Returns { txHash: string }.

estimateFee(params)

Quick fee estimate without building the full transaction. Useful for showing fees in the UI before the user initiates a transfer.

buildTransfer params

TypeScript

{
  sender: string,       // Wallet address of the sender
  recipient: string,    // Destination address
  amount: string,       // Amount in smallest units (e.g. '1000000' = 1 USDC)
  assetType: string,    // Token contract address (see Supported Tokens below)
  decimals: number,     // Token decimals (e.g. 6 for USDC)
  symbol: string,       // Token symbol (e.g. 'USDC')
}

Supported Tokens — Script Composer

Mainnet stablecoin asset addresses for use with ScriptComposerClient. Testnet supports the same symbols on the Aptos testnet.

Symbol	Name	Decimals	Mainnet assetType
USDC	USD Coin	6	0xbae207659db88bea0cbead6da0ed00aac12edcdda169e591cd41c94180b46f3b
USDT	Tether USD	6	0x357b0b74bc833e95a115ad22604854d6b0fca151cecd94111770e5d6ffc9dc2b
WBTC	Wrapped Bitcoin	8	0x68c2185f5e2023f2e4401ba56b66c8ae2cfcf8a27852e70eb78b03f59a652a3d
USDe	USDe (Ethena)	6	0xf37a4a75f89b79985c1fcb42d0a87f4bde28cc2b46c4dd01d9a8428e7726e2e9
USD1	USD1 (World Liberty)	6	0x05fa02d0fa44a90ad59fb90adb08e24c4efbc98eb9e9f2d0d9c0ad18d7fc9d2

Error Handling

Both classes throw SmoothSendError on failure. Always wrap in try/catch.

transfer.ts

TypeScript

1import { SmoothSendError } from '@smoothsend/sdk';
2 
3try {
4  const result = await signAndSubmitTransaction(transaction);
5  console.log('Success:', result.hash);
6} catch (error) {
7  if (error instanceof SmoothSendError) {
8    switch (error.statusCode) {
9      case 401: console.error('Invalid API key'); break;
10      case 402: console.error('Insufficient credits — top up your dashboard'); break;
11      case 429: console.error('Rate limit exceeded — slow down requests'); break;
12      default:  console.error('SmoothSend error:', error.message);
13    }
14  } else {
15    console.error('Wallet or network error:', error);
16  }
17}

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