Starknet Wallet Skill

Manage Starknet wallets for AI agents with native Account Abstraction support.

When to Use

• Creating, funding, and operating Starknet accounts for agent workflows.
• Checking balances, sending transfers, managing session keys, or invoking contracts from an agent wallet.

When NOT to Use

• DeFi-specific routing, staking, or lending flows better covered by starknet-defi.
• Cairo contract authoring, deployment-only operations, or security auditing.

Quick Start

1. Install the SDK dependencies and set Starknet RPC/account environment variables.
2. Use skills catalog to pivot to adjacent modules like DeFi, deployment, or auditing.

Prerequisites

npm install starknet@^8.9.1 @avnu/avnu-sdk@^4.0.1

Environment variables:

STARKNET_RPC_URL=https://starknet-mainnet.g.alchemy.com/v2/YOUR_KEY
STARKNET_ACCOUNT_ADDRESS=0x...
STARKNET_PRIVATE_KEY=0x...
AVNU_BASE_URL=https://starknet.api.avnu.fi (optional)
AVNU_PAYMASTER_URL=https://starknet.paymaster.avnu.fi (optional)
AVNU_PAYMASTER_API_KEY=your_key (optional, for free gas)

Available MCP Tools

The Starknet MCP Server provides these tools for wallet operations:

Tool	Purpose	Key Features
starknet_get_balance	Check single token balance	Simple, fast queries
starknet_get_balances	Check multiple token balances	Batch queries (up to 200 tokens), single RPC call
starknet_transfer	Send tokens	Supports gasless mode (paymaster)
starknet_call_contract	Read contract state	Call view functions
starknet_invoke_contract	Execute contract functions	Write operations, supports gasless
starknet_swap	Execute token swaps	AVNU integration, best price routing
starknet_get_quote	Get swap quotes	Price estimation before swap
starknet_register_agent	Register agent identity	ERC-8004 on-chain identity

Balance Tools Detail

starknet_get_balance (Single Token)

Query balance for one token. Use for simple cases.

Input:

• token (required): Token symbol (ETH, STRK, USDC, USDT) or contract address
• address (optional): Wallet address (defaults to agent's address)

Response:

{
  "address": "0x...",
  "token": "ETH",
  "tokenAddress": "0x049d36570d4e46f48e99674bd3fcc84644ddd6b96f7c741b1562b82f9e004dc7",
  "balance": "1.5",
  "raw": "1500000000000000000",
  "decimals": 18
}

starknet_get_balances (Multiple Tokens)

Query balances for multiple tokens in a single RPC call. More efficient for portfolio views.

Input:

• tokens (required): Array of token symbols or addresses (max 200)
• address (optional): Wallet address

Response:

{
  "address": "0x...",
  "balances": [
    { "token": "ETH", "tokenAddress": "0x...", "balance": "1.5", "raw": "...", "decimals": 18 },
    { "token": "USDC", "tokenAddress": "0x...", "balance": "100", "raw": "...", "decimals": 6 }
  ],
  "tokensQueried": 2,
  "method": "balance_checker"
}

When to use:

• starknet_get_balance: Quick single-token check
• starknet_get_balances: Portfolio overview, multi-token operations

Core Operations

Check Balance (Single Token)

Use the starknet_get_balance MCP tool for simple single-token queries:

// Via MCP tool (recommended)
const result = await mcpClient.callTool({
  name: "starknet_get_balance",
  arguments: {
    address: "0x...",  // Account address
    token: "ETH",      // Symbol (ETH, STRK, USDC, USDT) or contract address
  }
});
// Returns: { address, token, tokenAddress, balance, raw, decimals }

Direct starknet.js usage:

import { RpcProvider, Contract } from "starknet";

const provider = new RpcProvider({ nodeUrl: process.env.STARKNET_RPC_URL });

// ETH balance (starknet.js v8 uses options object for Contract)
const ethAddress = "0x049d36570d4e46f48e99674bd3fcc84644ddd6b96f7c741b1562b82f9e004dc7";
const ethContract = new Contract({
  abi: erc20Abi,
  address: ethAddress,
  providerOrAccount: provider,
});
const balance = await ethContract.balanceOf(accountAddress);

// starknet.js v8: Convert uint256 to bigint
const balanceBigInt = BigInt(balance.low) + (BigInt(balance.high) << 128n);
// Format: (balanceBigInt / 10n ** 18n).toString() for whole units

Check Multiple Balances (Batch)

Use starknet_get_balances for efficient multi-token queries (single RPC call):

// Via MCP tool (recommended for multiple tokens)
const result = await mcpClient.callTool({
  name: "starknet_get_balances",
  arguments: {
    address: "0x...",
    tokens: ["ETH", "STRK", "USDC", "USDT"],  // Up to 200 tokens
  }
});

// Returns:
// {
//   address: "0x...",
//   balances: [
//     { token: "ETH", tokenAddress: "0x...", balance: "1.5", raw: "1500000000000000000", decimals: 18 },
//     { token: "STRK", tokenAddress: "0x...", balance: "100", raw: "100000000000000000000", decimals: 18 },
//     ...
//   ],
//   tokensQueried: 4,
//   method: "balance_checker"  // Uses BalanceChecker contract for efficiency
// }

Direct starknet.js usage with BalanceChecker contract:

import { RpcProvider, Contract } from "starknet";

const provider = new RpcProvider({ nodeUrl: process.env.STARKNET_RPC_URL });

// BalanceChecker contract (returns non-zero balances only)
const BALANCE_CHECKER_ADDRESS = "0x031ce64a666fbf9a2b1b2ca51c2af60d9a76d3b85e5fbfb9d5a8dbd3fedc9716";
const BALANCE_CHECKER_ABI = [
  {
    type: "struct",
    name: "core::integer::u256",
    members: [
      { name: "low", type: "core::integer::u128" },
      { name: "high", type: "core::integer::u128" },
    ],
  },
  {
    type: "struct",
    name: "governance::balance_checker::NonZeroBalance",
    members: [
      { name: "token", type: "core::starknet::contract_address::ContractAddress" },
      { name: "balance", type: "core::integer::u256" },
    ],
  },
  {
    type: "function",
    name: "get_balances",
    inputs: [
      { name: "address", type: "core::starknet::contract_address::ContractAddress" },
      { name: "tokens", type: "core::array::Span::<core::starknet::contract_address::ContractAddress>" },
    ],
    outputs: [{ type: "core::array::Span::<governance::balance_checker::NonZeroBalance>" }],
    state_mutability: "view",
  },
];

const balanceChecker = new Contract({
  abi: BALANCE_CHECKER_ABI,
  address: BALANCE_CHECKER_ADDRESS,
  providerOrAccount: provider,
});

// Query multiple tokens at once
const tokens = [
  "0x049d36570d4e46f48e99674bd3fcc84644ddd6b96f7c741b1562b82f9e004dc7", // ETH
  "0x04718f5a0fc34cc1af16a1cdee98ffb20c31f5cd61d6ab07201858f4287c938d", // STRK
  "0x053c91253bc9682c04929ca02ed00b3e423f6710d2ee7e0d5ebb06f3ecf368a8", // USDC
];

const result = await balanceChecker.get_balances(accountAddress, tokens);

// Parse response (only non-zero balances returned)
for (const item of result) {
  const tokenAddr = "0x" + BigInt(item.token).toString(16).padStart(64, "0");
  const balance = BigInt(item.balance); // starknet.js converts u256 to bigint
  console.log(`${tokenAddr}: ${balance}`);
}

When to use which:

• starknet_get_balance: Single token, simple use case
• starknet_get_balances: Multiple tokens, portfolio view, more efficient

Transfer Tokens

Use the starknet_transfer MCP tool with optional gasless mode:

// Via MCP tool (recommended)
const result = await mcpClient.callTool({
  name: "starknet_transfer",
  arguments: {
    recipient: "0x...",
    token: "STRK",        // Symbol or contract address
    amount: "10.5",       // Human-readable amount
    gasfree: false,       // Optional: use paymaster
  }
});
// Returns: { transactionHash, recipient, token, amount, gasfree }

Gasless Transfer (Pay gas in token instead of ETH/STRK):

// Pay gas in USDC instead of ETH/STRK
const result = await mcpClient.callTool({
  name: "starknet_transfer",
  arguments: {
    recipient: "0x...",
    token: "STRK",
    amount: "100",
    gasfree: true,
    gasToken: "USDC",    // Gas paid in USDC
  }
});

Direct starknet.js usage:

import { Account, RpcProvider, CallData, cairo, ETransactionVersion } from "starknet";

const provider = new RpcProvider({ nodeUrl: process.env.STARKNET_RPC_URL });

// starknet.js v8: Account uses options object
const account = new Account({
  provider,
  address: process.env.STARKNET_ACCOUNT_ADDRESS,
  signer: process.env.STARKNET_PRIVATE_KEY,
  transactionVersion: ETransactionVersion.V3,
});

const tokenAddress = "0x04718f5a0fc34cc1af16a1cdee98ffb20c31f5cd61d6ab07201858f4287c938d"; // STRK

// starknet.js v8: Use cairo.uint256() instead of uint256.bnToUint256()
const { transaction_hash } = await account.execute({
  contractAddress: tokenAddress,
  entrypoint: "transfer",
  calldata: CallData.compile({
    recipient: recipientAddress,
    amount: cairo.uint256(amountInWei),
  }),
});
await account.waitForTransaction(transaction_hash);

Estimate Fees

const estimatedFee = await account.estimateInvokeFee({
  contractAddress: tokenAddress,
  entrypoint: "transfer",
  calldata: CallData.compile({
    recipient: recipientAddress,
    amount: cairo.uint256(amountInWei),
  }),
});
// estimatedFee.overall_fee -- total fee in STRK (V3 transactions)

Contract Interactions

Read contract state (view functions):

// Via MCP tool
const result = await mcpClient.callTool({
  name: "starknet_call_contract",
  arguments: {
    contractAddress: "0x...",
    entrypoint: "balanceOf",
    calldata: [accountAddress],
  }
});

Write to contracts (state-changing functions):

// Via MCP tool with gasless option
const result = await mcpClient.callTool({
  name: "starknet_invoke_contract",
  arguments: {
    contractAddress: "0x...",
    entrypoint: "approve",
    calldata: [spenderAddress, ...uint256Amount],
    gasfree: true,         // Optional: use paymaster
    gasToken: "USDC",      // Optional: pay gas in token
  }
});

Multi-Call (Batch Transactions)

// Execute multiple operations in a single transaction
const { transaction_hash } = await account.execute([
  {
    contractAddress: tokenA,
    entrypoint: "approve",
    calldata: CallData.compile({
      spender: routerAddress,
      amount: cairo.uint256(amount),
    }),
  },
  {
    contractAddress: routerAddress,
    entrypoint: "swap",
    calldata: CallData.compile({ /* swap params */ }),
  },
]);

Gasless Transfer (Pay Gas in Token) - SDK v4 + PaymasterRpc

import { getQuotes, executeSwap } from "@avnu/avnu-sdk";
import { PaymasterRpc } from "starknet";

// SDK v4: Use PaymasterRpc from starknet.js
// Mainnet: https://starknet.paymaster.avnu.fi
// Sepolia: https://sepolia.paymaster.avnu.fi
const paymaster = new PaymasterRpc({
  nodeUrl: process.env.AVNU_PAYMASTER_URL || "https://starknet.paymaster.avnu.fi",
});

// Any swap can be made gasless by adding paymaster option
const result = await executeSwap({
  provider: account,
  quote: bestQuote,
  slippage: 0.01,
  executeApprove: true,
  paymaster: {
    active: true,
    provider: paymaster,
    params: {
      feeMode: {
        mode: "default",
        gasToken: usdcAddress, // Pay gas in USDC instead of ETH/STRK
      },
    },
  },
});

Token Resolution

The MCP server uses TokenService to resolve token symbols and addresses. Static tokens (ETH, STRK, USDC, USDT) are always available. For other tokens, the service fetches metadata from avnu SDK.

import { fetchTokenByAddress, fetchVerifiedTokenBySymbol } from '@avnu/avnu-sdk';

// Get token by symbol (verified tokens only)
const lords = await fetchVerifiedTokenBySymbol('LORDS');
console.log(lords.address, lords.decimals); // 0x0124aeb..., 18

// Get token by address (any token)
const token = await fetchTokenByAddress('0x...');
console.log(token.symbol, token.name, token.decimals);

// Get all verified tokens
import { fetchTokens } from '@avnu/avnu-sdk';
const page = await fetchTokens({ tags: ['Verified'], size: 100 });
page.content.forEach(t => console.log(t.symbol, t.address));

Static tokens available without network calls: ETH, STRK, USDC, USDT

Session Keys (Agent Autonomy)

Session keys allow agents to execute pre-approved transactions without per-action human approval:

1. Human owner creates a session key with policies:
   • Allowed contract addresses and methods
   • Maximum spending per transaction/period
   • Expiry timestamp
2. Agent uses the session key for autonomous operations
3. Owner can revoke at any time

Reference implementation: Cartridge Controller

Configuration

Variable	Purpose	Default
STARKNET_RPC_URL	Starknet JSON-RPC endpoint	Required
STARKNET_ACCOUNT_ADDRESS	Agent's account address	Required
STARKNET_PRIVATE_KEY	Agent's signing key	Required
AVNU_BASE_URL	avnu API base URL	https://starknet.api.avnu.fi
AVNU_PAYMASTER_URL	avnu paymaster URL	https://starknet.paymaster.avnu.fi

Error Handling

Error	Cause	Resolution
INSUFFICIENT_BALANCE	Not enough tokens	Check balance before transfer
INVALID_NONCE	Nonce mismatch	Retry with fresh nonce
TRANSACTION_REVERTED	Contract execution failed	Check calldata and allowances
FEE_TRANSFER_FAILURE	Can't pay gas fee	Use paymaster or add ETH/STRK

References

• starknet.js Documentation
• Starknet Account Abstraction
• Session Keys Guide
• avnu Paymaster