Show HN: Send21 – Crypto pay links an AI agent can create but can't spend

Testnet demo. You sign with your own wallet, on test networks only. The coins are free test coins from public faucets and have no value.

See the whole flow in a few minutes, with no account and no email. send21 creates a payment draft, you pay it from your own wallet, and the page shows the confirmation from a public test network.

How it works #

1. send21 creates a payment draft , with the same draft-only access an AI agent gets. Nothing here can spend.
2. You check and sign in your own wallet . send21 never holds keys, never signs and never broadcasts.
3. send21 watches the chain until the payment confirms. In a real integration your backend gets a signed draft.confirmed webhook at that moment.

Need test coins? Faucets #

For AI agents: the same flow over API or MCP #

An agent gets a scoped API key that can create and track drafts but never spend. A person always signs in their own wallet. Test networks on send21.io are for this demo only, and account drafts use the live networks. That is still safe while you integrate: a draft moves no money until someone signs it, so create small drafts to your own address and cancel them.

curl -X POST https://send21.io/api/v1/drafts \
  -H "Authorization: Bearer s21_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: agent-demo-001" \
  -d '{
    "receiverAddress": "0x...your-own-address",
    "network": "Base",
    "currency": "Usdc",
    "paymentMethod": "MultiOutput",
    "singleOutput": true,
    "amountSats": 1000000,
    "memo": "agent integration test, 1 USDC"
  }'
// MCP (Streamable HTTP), same key, same draft-only scopes
{
  "mcpServers": {
    "send21": {
      "url": "https://send21.io/mcp",
      "headers": { "Authorization": "Bearer s21_YOUR_KEY" }
    }
  }
}
// then call the create_draft tool with { "network": "Base", "currency": "Usdc", ... }

Full API: /swagger | agent overview: /llms.txt | status via GET /drafts/{id}/status or signed webhooks (draft.confirmed).

Ready for real payments? #

Create a free account and send your first pay link. No subscription, only a small fee per payment.