gas-station

Turnkey Gas Station SDK

A reusable SDK for implementing gasless transactions using EIP-7702, Turnkey wallet management, and your own paymaster. This package provides clean abstractions and utility methods to quickly integrate with Turnkey's contracts for sponsored transaction execution.

What is This?

This SDK enables you to:

• Bring your own paymaster to sponsor user transactions
• Use Turnkey for secure wallet management and transaction signing
• Execute gasless transactions via EIP-7702 delegation and EIP-712 signed intents
• Support any on-chain action through generic execution parameters

Perfect for building dApps where users don't need ETH for gas, enabling seamless onboarding and better UX.

How It Works

1. EIP-7702 Authorization: One-time setup where an EOA authorizes a gas station contract
2. EIP-712 Signed Intents: User signs off-chain intents for what they want to execute
3. Paymaster Execution: Your paymaster submits the transaction and pays for gas
4. Turnkey Integration: All signatures handled securely through Turnkey

Quick Start

1. Install Dependencies

pnpm install @turnkey/gas-station @turnkey/sdk-server @turnkey/viem viem

2. Set Up Environment

Create .env.local:

# Turnkey Configuration
BASE_URL=https://api.turnkey.com
API_PRIVATE_KEY=your_turnkey_api_private_key
API_PUBLIC_KEY=your_turnkey_api_public_key
ORGANIZATION_ID=your_turnkey_organization_id

# Wallet Addresses
EOA_ADDRESS=0x...                            # User's wallet address
PAYMASTER_ADDRESS=0x...                      # Your paymaster address

# RPC Configuration
BASE_RPC_URL=https://mainnet.base.org
ETH_RPC_URL=https://eth-mainnet.g.alchemy.com/v2/...

# Gas Station Contracts (Optional - defaults to deterministic addresses)
DELEGATE_CONTRACT=0x...    # EIP-7702 delegate contract
EXECUTION_CONTRACT=0x...   # Gas Sponsorship entrypoint contract which calls the delegate.

Note: The gas station contracts are currently deployed at deterministic addresses on the following chains:

• Ethereum Mainnet
• Base Mainnet

These addresses are built into the SDK, so you don't need to specify them unless you are using custom deployments.

3. Initialize and Use

import { GasStationClient } from "@turnkey/gas-station";
import { Turnkey } from "@turnkey/sdk-server";
import { createAccount } from "@turnkey/viem";
import { parseEther, parseUnits, createWalletClient, http } from "viem";
import { base } from "viem/chains";

// Initialize Turnkey
const turnkeyClient = new Turnkey({
  apiBaseUrl: process.env.BASE_URL!,
  apiPrivateKey: process.env.API_PRIVATE_KEY!,
  apiPublicKey: process.env.API_PUBLIC_KEY!,
  defaultOrganizationId: process.env.ORGANIZATION_ID!,
});

// Create Turnkey accounts
const userAccount = await createAccount({
  client: turnkeyClient.apiClient(),
  organizationId: process.env.ORGANIZATION_ID!,
  signWith: process.env.EOA_ADDRESS as `0x${string}`,
});

const paymasterAccount = await createAccount({
  client: turnkeyClient.apiClient(),
  organizationId: process.env.ORGANIZATION_ID!,
  signWith: process.env.PAYMASTER_ADDRESS as `0x${string}`,
});

// Create viem wallet clients
const userWalletClient = createWalletClient({
  account: userAccount,
  chain: base,
  transport: http(process.env.BASE_RPC_URL!),
});

const paymasterWalletClient = createWalletClient({
  account: paymasterAccount,
  chain: base,
  transport: http(process.env.BASE_RPC_URL!),
});

// Create Gas Station clients
const userClient = new GasStationClient({
  walletClient: userWalletClient,
});

const paymasterClient = new GasStationClient({
  walletClient: paymasterWalletClient,
});

// One-time: Authorize the EOA to use gas station
const authorization = await userClient.signAuthorization();
await paymasterClient.submitAuthorizations([authorization]);

// Execute a gasless ETH transfer
let nonce = await userClient.getNonce();
const ethIntent = await userClient
  .createIntent()
  .transferETH("0xRecipient...", parseEther("0.1"))
  .sign(nonce);
await paymasterClient.execute(ethIntent);

// Execute a gasless token transfer
nonce = await userClient.getNonce();
const usdcIntent = await userClient
  .createIntent()
  .transferToken(
    "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", // USDC on Base
    "0xRecipient...",
    parseUnits("10", 6),
  )
  .sign(nonce);
await paymasterClient.execute(usdcIntent);

Core API

GasStationClient

Main client for gas station operations. Each client instance wraps a viem wallet client.

Constructor

new GasStationClient({
  walletClient: WalletClient,          // Viem wallet client (e.g., with Turnkey account)
  delegateContract?: `0x${string}`,    // Optional: defaults to deterministic address
  executionContract?: `0x${string}`,   // Optional: defaults to deterministic address
})

Methods

End User Methods (call with user client):

signAuthorization(): Promise<SignedAuthorization>

• Sign an EIP-7702 authorization for the gas station contract
• Returns authorization that can be submitted by paymaster

createIntent(): IntentBuilder

• Create a builder for composing transactions
• Intent must be signed before execution

getNonce(address?: Address): Promise<bigint>

• Get current nonce from gas station contract
• Defaults to the signer's address if not specified

Paymaster Methods (call with paymaster client):

submitAuthorizations(authorizations: SignedAuthorization[]): Promise<{ txHash, blockNumber }>

• Submit signed EIP-7702 authorization transaction(s)
• Supports authorizing multiple EOAs in a single transaction
• Paymaster pays for gas

execute(intent: ExecutionIntent): Promise<{ txHash, blockNumber, gasUsed }>

• Execute a signed intent through the gas station
• Paymaster pays for gas

IntentBuilder

Composable builder for complex multi-step transactions.

const nonce = await userClient.getNonce();
const builder = userClient.createIntent();

const intent = await builder
  .transferToken(usdcAddress, recipient, amount)
  .sign(nonce);

await paymasterClient.execute(intent);

Common Use Cases

Simple Payment

// Gasless USDC payment
const nonce = await userClient.getNonce();
const intent = await userClient
  .createIntent()
  .transferToken(usdcAddress, recipientAddress, parseUnits("50", 6))
  .sign(nonce);

const result = await paymasterClient.execute(intent);
console.log(`Payment sent: ${result.txHash}`);

Token Approval + DEX Swap

// Step 1: Approve DEX to spend tokens
let nonce = await userClient.getNonce();
const approvalIntent = await userClient
  .createIntent()
  .approveToken(usdcAddress, dexAddress, parseUnits("100", 6))
  .sign(nonce);
await paymasterClient.execute(approvalIntent);

// Step 2: Execute swap
nonce = await userClient.getNonce();
const swapIntent = await userClient
  .createIntent()
  .callContract({
    contract: dexAddress,
    abi: DEX_ABI,
    functionName: "swapExactTokensForTokens",
    args: [amountIn, amountOutMin, path, recipient, deadline],
  })
  .sign(nonce);
await paymasterClient.execute(swapIntent);

User Onboarding

async function onboardUser(userAddress: string) {
  // Create viem wallet client for user
  const userAccount = await createAccount({
    client: turnkeyClient.apiClient(),
    organizationId: ORGANIZATION_ID,
    signWith: userAddress as `0x${string}`,
  });

  const userWalletClient = createWalletClient({
    account: userAccount,
    chain: base,
    transport: http(BASE_RPC_URL),
  });

  // Create Gas Station clients
  const userClient = new GasStationClient({
    walletClient: userWalletClient,
  });

  // Authorize user (paymaster pays)
  const authorization = await userClient.signAuthorization();
  await paymasterClient.submitAuthorizations([authorization]);

  // User can now execute transactions without ETH
  console.log("✅ User ready for gasless transactions!");
}

Architecture

Gas Station Pattern

1. Delegate Contract: Authorized to EOA via EIP-7702
2. Execution Contract: Contains execution logic and nonce management
3. EOA: Signs EIP-712 intents off-chain
4. Paymaster: Submits transactions and pays gas

Transaction Flow

User (EOA)
  ↓ Signs EIP-712 intent off-chain
  ↓
SDK (GasStationClient)
  ↓ Builds transaction
  ↓
Paymaster
  ↓ Submits transaction, pays gas
  ↓
Gas Station Contract
  ↓ Validates signature & nonce
  ↓ Executes on behalf of EOA
  ↓
Target Contract (USDC, NFT, DEX, etc.)

Chain Support

Available presets for quick setup:

• BASE_MAINNET - Base mainnet (includes USDC address)
• ETHEREUM_MAINNET - Ethereum mainnet (includes USDC address)

// Chain presets are available for quick configuration
import { CHAIN_PRESETS, GasStationClient } from "@turnkey/gas-station";
import { createWalletClient, http } from "viem";

const basePreset = CHAIN_PRESETS.BASE_MAINNET;
const userWalletClient = createWalletClient({
  account: userAccount,
  chain: basePreset.chain,
  transport: http(basePreset.rpcUrl),
});

const userClient = new GasStationClient({
  walletClient: userWalletClient,
});

Security

• EIP-712 Signed Intents: All executions require valid typed signatures
• EIP-7702 Scoping: Authorization is per-EOA and can be revoked
• Deadline Enforcement: Each transaction includes a deadline (Unix timestamp) to prevent replay attacks; signatures expire after this time
• Turnkey Integration: Private keys never leave Turnkey's secure infrastructure

Security Policies

Turnkey policies provide additional security layers by restricting what transactions can be signed and executed. The Gas Station SDK includes helpers for creating these policies.

EOA Intent Signing Policies

Restrict what EIP-712 intents the EOA can sign:

import { buildIntentSigningPolicy } from "@turnkey/gas-station";

// USDC-only policy
const eoaPolicy = buildIntentSigningPolicy({
  organizationId: "a5b89e4f-1234-5678-9abc-def012345678",
  eoaUserId: "3c7d6e8a-4b5c-6d7e-8f9a-0b1c2d3e4f5a",
  restrictions: {
    allowedContracts: ["0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"], // USDC on Base
    disallowEthTransfer: true, // Disallow ETH transfers
  },
  policyName: "USDC Only Policy",
});

// Resulting policy restricts signing to USDC transfers only:
// {
//   organizationId: "a5b89e4f-1234-5678-9abc-def012345678",
//   policyName: "USDC Only Policy",
//   effect: "EFFECT_ALLOW",
//   consensus: "approvers.any(user, user.id == '3c7d6e8a-4b5c-6d7e-8f9a-0b1c2d3e4f5a')",
//   condition: "activity.resource == 'PRIVATE_KEY' && " +
//              "activity.action == 'SIGN' && " +
//              "eth.eip_712.primary_type == 'Execution' && " +
//              "(eth.eip_712.message['to'] == '0x833589fcd6edb6e08f4c7c32d4f71b54bda02913') && " +
//              "eth.eip_712.message['value'] == '0'",
//   notes: "Restricts which EIP-712 intents the EOA can sign for gas station execution"
// }

Paymaster Execution Policies

Restrict what on-chain transactions the paymaster can submit:

import {
  buildPaymasterExecutionPolicy,
  DEFAULT_EXECUTION_CONTRACT,
  ensureGasStationInterface,
} from "@turnkey/gas-station";
import { parseGwei, parseEther } from "viem";

// First, ensure the Gas Station ABI is uploaded (enables ABI-based policies)
await ensureGasStationInterface(
  turnkeyClient.apiClient(),
  "your-org-id",
  DEFAULT_EXECUTION_CONTRACT,
  undefined,
  "Base Mainnet",
);

// Paymaster protection policy with ETH amount limit
const paymasterPolicy = buildPaymasterExecutionPolicy({
  organizationId: "f8c3a5e7-9876-5432-1abc-def098765432",
  paymasterUserId: "8f2a1b4c-5d6e-7f8a-9b0c-1d2e3f4a5b6c",
  executionContractAddress: DEFAULT_EXECUTION_CONTRACT,
  restrictions: {
    allowedEOAs: ["0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb"],
    allowedContracts: ["0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"],
    maxEthAmount: parseEther("0.1"), // Max 0.1 ETH per EOA transaction
    maxGasPrice: parseGwei("50"), // Max 50 gwei gas price
    maxGasLimit: 500000n, // Max 500k gas limit
  },
  policyName: "Paymaster Protection",
});

// Resulting policy uses ABI parsing for direct argument access:
// {
//   organizationId: "f8c3a5e7-9876-5432-1abc-def098765432",
//   policyName: "Paymaster Protection",
//   effect: "EFFECT_ALLOW",
//   consensus: "approvers.any(user, user.id == '8f2a1b4c-5d6e-7f8a-9b0c-1d2e3f4a5b6c')",
//   condition: "activity.resource == 'PRIVATE_KEY' && " +
//              "activity.action == 'SIGN' && " +
//              "eth.tx.to == '0x00000000008c57a1ce37836a5e9d36759d070d8c' && " +
//              "(eth.tx.contract_call_args['_to'] == '0x833589fcd6edb6e08f4c7c32d4f71b54bda02913') && " +
//              "(eth.tx.contract_call_args['_target'] == '0x742d35cc6634c0532925a3b844bc9e7595f0beb') && " +
//              "eth.tx.contract_call_args['_ethAmount'] <= 100000000000000000 && " +
//              "eth.tx.gasPrice <= 50000000000 && " +
//              "eth.tx.gas <= 500000",
//   notes: "Restricts which transactions the paymaster can execute on the gas station"
// }

Note: The ensureGasStationInterface() function uploads the Gas Station ABI to Turnkey's Smart Contract Interface feature. This enables Turnkey's policy engine to parse the ABI-encoded transaction data and directly compare the _ethAmount parameter as a uint256 value, rather than raw bytes. The function checks if the ABI already exists before uploading to avoid duplicates.

Defense in Depth

Combine both policy types for maximum security:

import {
  buildIntentSigningPolicy,
  buildPaymasterExecutionPolicy,
  DEFAULT_EXECUTION_CONTRACT,
} from "@turnkey/gas-station";
import { parseGwei } from "viem";

// Layer 1: EOA can only sign USDC intents
const eoaPolicy = buildIntentSigningPolicy({
  organizationId: "a5b89e4f-1234-5678-9abc-def012345678",
  eoaUserId: "3c7d6e8a-4b5c-6d7e-8f9a-0b1c2d3e4f5a",
  restrictions: {
    allowedContracts: ["0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"],
    disallowEthTransfer: true, // No ETH transfers
  },
});

// Layer 2: Paymaster can only execute for specific users with gas limits
const paymasterPolicy = buildPaymasterExecutionPolicy({
  organizationId: "f8c3a5e7-9876-5432-1abc-def098765432",
  paymasterUserId: "8f2a1b4c-5d6e-7f8a-9b0c-1d2e3f4a5b6c",
  executionContractAddress: DEFAULT_EXECUTION_CONTRACT,
  restrictions: {
    allowedEOAs: ["0xUserAddress..."],
    allowedContracts: ["0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"],
    maxGasPrice: parseGwei("50"),
    maxGasLimit: 500000n,
  },
});

Advanced: Writing Custom Paymaster Policies

When using buildPaymasterExecutionPolicy, the SDK creates Turnkey policies that parse the transaction calldata to enforce restrictions. Understanding the transaction structure allows you to write custom policies for advanced use cases.

Transaction Data Structure

When the paymaster signs an execution transaction calling execute(address _target, address _to, uint256 _ethAmount, bytes _data), the transaction data (eth.tx.data) has the following structure:

Position in eth.tx.data	Length	Content	Example
[2..10]	8 chars	Function selector	6c5c2ed9 (execute)
[10..74]	64 chars	_target (EOA, padded)	0000...742d35cc6634c0532925a3b844bc9e7595f0beb
[74..138]	64 chars	_to (output contract)	0000...833589fcd6edb6e08f4c7c32d4f71b54bda02913
[138..202]	64 chars	_ethAmount (uint256)	0000...0000 (0 ETH) or amount in wei
[202..266]	64 chars	Offset to _data bytes	0000...0080 (128 bytes)
[266..330]	64 chars	Packed data length	0000...0055 (85 bytes: 65+16+4)
[330..460]	130 chars	Signature (65 bytes)	EIP-712 signature from EOA
[460..492]	32 chars	Nonce (16 bytes)	00000000000000000000000000000000
[492..500]	8 chars	Deadline (4 bytes)	6ac7d340 (Unix timestamp)
[500+]	Variable	Call data	Encoded function call for target contract

Important: Turnkey's eth.tx.data includes the 0x prefix, so positions start at index 2 (after 0x).

Note: The deadline is a Unix timestamp that prevents replay attacks by expiring signatures after a specified time. The SDK defaults to 1 hour, customizable with withDeadline().

Policy Conditions Reference

Check execution contract address:

eth.tx.to == "0x00000000008c57a1ce37836a5e9d36759d070d8c";

Check which EOA is executing:

eth.tx.data[10..74] == '0000000000000000000000742d35cc6634c0532925a3b844bc9e7595f0beb'

Check target contract (output contract):

eth.tx.data[74..138] == '0000000000000000000000833589fcd6edb6e08f4c7c32d4f71b54bda02913'

Check ETH amount:

eth.tx.data[138..202].hex_to_uint() <= 100000000000000000; // Max 0.1 ETH in wei

Check gas price:

eth.tx.gasPrice <= 50000000000; // 50 gwei in wei

Check gas limit:

eth.tx.gas <= 500000;

Example: Custom Multi-Contract Policy

Allow paymaster to execute for USDC or DAI only:

const policy = {
  organizationId: "f8c3a5e7-9876-5432-1abc-def098765432",
  policyName: "Stablecoin Execution Policy",
  effect: "EFFECT_ALLOW",
  consensus: `approvers.any(user, user.id == '${paymasterUserId}')`,
  condition: [
    "activity.resource == 'PRIVATE_KEY'",
    "activity.action == 'SIGN'",
    "eth.tx.to == '0x00000000008c57a1ce37836a5e9d36759d070d8c'",
    // Allow USDC or DAI
    "(eth.tx.data[74..138] == '0000000000000000000000833589fcd6edb6e08f4c7c32d4f71b54bda02913' || eth.tx.data[74..138] == '00000000000000000000006b175474e89094c44da98b954eedeac495271d0f')",
    // Gas limits
    "eth.tx.gasPrice <= 100000000000",
    "eth.tx.gas <= 500000",
  ].join(" && "),
  notes: "Allow USDC and DAI execution with gas limits",
};

await turnkeyClient.apiClient().createPolicy(policy);

Example: Whitelist Specific EOAs

Only allow execution for approved user wallets:

const approvedEOAs = [
  "0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb",
  "0x1234567890123456789012345678901234567890",
];

const eoaConditions = approvedEOAs
  .map((addr) => {
    const padded = addr.slice(2).toLowerCase().padStart(64, "0");
    return `eth.tx.data[10..74] == '${padded}'`;
  })
  .join(" || ");

const policy = {
  organizationId: "f8c3a5e7-9876-5432-1abc-def098765432",
  policyName: "Approved Users Only",
  effect: "EFFECT_ALLOW",
  consensus: `approvers.any(user, user.id == '${paymasterUserId}')`,
  condition: [
    "activity.resource == 'PRIVATE_KEY'",
    "activity.action == 'SIGN'",
    "eth.tx.to == '0x00000000008c57a1ce37836a5e9d36759d070d8c'",
    `(${eoaConditions})`,
  ].join(" && "),
};

await turnkeyClient.apiClient().createPolicy(policy);

Using the Helper Functions

For most cases, use the built-in helpers which handle the byte positions correctly:

import {
  buildPaymasterExecutionPolicy,
  DEFAULT_EXECUTION_CONTRACT,
} from "@turnkey/gas-station";
import { parseGwei } from "viem";

const policy = buildPaymasterExecutionPolicy({
  organizationId: subOrgId,
  paymasterUserId: paymasterUserId,
  executionContractAddress: DEFAULT_EXECUTION_CONTRACT,
  restrictions: {
    allowedContracts: [
      "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", // USDC
      "0x50c5725949A6F0c72E6C4a641F24049A917DB0Cb", // DAI
    ],
    allowedEOAs: ["0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb"],
    maxGasPrice: parseGwei("100"),
    maxGasLimit: 500000n,
  },
  policyName: "Production Paymaster Policy",
});

await turnkeyClient.apiClient().createPolicy(policy);

The helper functions automatically:

• Convert addresses to lowercase
• Add proper padding for EOA addresses
• Calculate correct byte positions (accounting for 0x prefix)
• Generate proper OR conditions for multiple allowed values

Troubleshooting

Authorization Failed

• Ensure paymaster has ETH for gas
• Verify delegate contract address is correct

Execution Failed

• Confirm EOA is authorized (check with isAuthorized())
• Verify execution contract address matches deployment
• Check nonce hasn't been reused
• Ensure target contract call is valid

Insufficient Funds

• EOA must have sufficient token balance for transfers
• Paymaster must have ETH for gas

Invalid Signature

• Verify EOA address is correct
• Ensure chain ID matches the network
• Check intent was signed with correct nonce

Best Practices

1. Client Separation: Create separate client instances for users and paymasters
2. Authorization: Only call authorize() once per EOA
3. Nonce Management: Always fetch fresh nonce before creating intents
4. Rate Limiting: Implement paymaster rate limits to prevent abuse

License

See the main SDK repository for license information.