crossmint

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:

Format	Example	Use Case
Email	email:[e-mail]:solana	Link wallet to email
User ID	userId:abc123:solana	Link wallet to custom user ID
Bare address	9bcWvn6HSMK9WoiUktc2MJ4ht2CGn389b4wMAQRTrCjZ	Reference by address

✅ 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

MCP Tool	Description	Notes
crossmint_create_wallet	Create custodial wallet	Pass email or userId
crossmint_get_balance	Get wallet balances	Must specify tokens array
crossmint_transfer	Transfer tokens	Between wallets
crossmint_sign_transaction	Sign & send transaction	Auto base64→base58 conversion

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

MCP Tool	Description
crossmint_mint_nft	Mint NFT to recipient

Virtual Cards

MCP Tool	Description
crossmint_create_card	Create virtual debit card

Payouts (Off-Ramp)

MCP Tool	Description
crossmint_create_payout	Payout crypto to bank/wallet

MCP Tool Usage

Create Wallet

{
  "type": "solana-custodial-wallet",
  "email": "[e-mail]"
}

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: "[e-mail]"
});

// 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"
});