name: crossmint description: Crossmint provides custodial wallet-as-a-service, NFT minting, virtual debit cards, crypto-to-fiat payouts, and transaction signing on Solana. Perfect for AI agents managing DeFi operations without needing a local keypair.

Crossmint — Wallets & Payments Skill

Overview

Crossmint provides custodial wallet-as-a-service, NFT minting, virtual debit cards, crypto-to-fiat payouts, and transaction signing on Solana. Perfect for AI agents managing DeFi operations without needing a local keypair.

Authentication

• Header: X-API-KEY: sk_staging_... or sk_production_...
• Staging (devnet): https://staging.crossmint.com/api
• Production (mainnet): https://www.crossmint.com/api
• Environment variable: CROSSMINT_ENVIRONMENT — set to production for mainnet

Important: Wallets created on production only exist on mainnet. Staging uses devnet addresses.

Wallet Locator Formats

Crossmint uses locator strings to identify wallets:

✅ Fixed: All endpoints now accept bare addresses directly. The SDK no longer adds solana: prefix.

API Request Format

Write endpoints (transfer, signTransaction, signMessage, fund) wrap the body in a params object:

{
  "params": {
    "transaction": "base58-encoded-tx"
  }
}

The SDK handles this wrapping automatically.

✅ Fixed: The encoding parameter is no longer accepted by Crossmint. Base58 is the default and only format.

Capabilities

Wallet Management

Signing Flow (Critical for DeFi)

Custodial wallets don't expose keypairs. Use this flow:

1. Get unsigned tx from Breeze/DFlow (returns base64)
2. crossmint_sign_transaction(locator, tx) → auto-converts to base58 & signs
3. Returns { id, status, onChain: { transaction, lastValidBlockHeight } }

Transaction encoding:

• ✅ Breeze/DFlow return base64
• ✅ Crossmint expects base58
• ✅ crossmint_sign_transaction MCP tool auto-converts

Response format changed:

• Old: { actionId, transactionHash }
• New: { id, status, onChain: { transaction, lastValidBlockHeight } }

NFT Minting

Virtual Cards

Payouts (Off-Ramp)

MCP Tool Usage

Create Wallet

{
  "type": "solana-custodial-wallet",
  "email": "user@example.com"
}

Returns wallet with address. Wallets are persistent across sessions with same email+API key.

Get Balance

{
  "locator": "9bcWvn6HSMK9WoiUktc2MJ4ht2CGn389b4wMAQRTrCjZ",
  "tokens": ["sol", "usdc"]
}

Required: Must specify tokens array.

Sign Transaction

{
  "locator": "9bcWvn6HSMK9WoiUktc2MJ4ht2CGn389b4wMAQRTrCjZ",
  "transaction": "<base64 or base58 transaction>"
}

Auto-detects format and converts base64→base58 if needed.

Example Workflow

// 1. Create wallet
const wallet = await crossmint_create_wallet({
  type: "solana-custodial-wallet",
  email: "agent@example.com"
});

// 2. Check balance
const balances = await crossmint_get_balance({
  locator: wallet.address,
  tokens: ["sol", "usdc"]
});

// 3. Get unsigned tx from Breeze (returns base64)
const depositTx = await breeze_deposit({
  userId: wallet.address,
  amount: "0.1",  // Human-readable
  mint: "So11111111111111111111111111111111111111112"
});

// 4. Sign and send (auto-converts base64→base58)
const result = await crossmint_sign_transaction({
  locator: wallet.address,
  transaction: depositTx.transaction
});

console.log("Transaction ID:", result.id);
console.log("Tx Hash:", result.onChain.transaction);

Known Issues & Fixes

✅ Locator format: No longer adds solana: prefix (caused 400 errors) ✅ Encoding parameter: Removed (Crossmint rejected it) ✅ Response format: Now returns { id, status, onChain } instead of { actionId, transactionHash } ✅ Base64/Base58: MCP tool auto-converts for you

Common Gotchas

• Balances require tokens array — You must specify which tokens to query
• Write endpoints wrap params — SDK handles this automatically
• Persistent wallets — Same email+API key = same wallet across sessions
• Production vs Staging — Wallets don't exist across environments

Installation

npm install agent-finance-sdk

import { CrossmintClient } from "agent-finance-sdk";

const cm = new CrossmintClient({
  apiKey: "sk_production_...",
  environment: "production"
});