send21 MCP

Remote Model Context Protocol server for send21: crypto pay links and API for people and AI agents.

send21 prepares payment instructions for BTC (on-chain and Lightning), USDC, USDT, EURC, SOL and ETH. The payer signs in their own wallet. send21 never holds keys, never signs, and never broadcasts.

Live endpoint (Streamable HTTP): https://send21.io/mcp (API key), https://send21.io/mcp/oauth (OAuth sign-in)
Descriptor: https://send21.io/.well-known/mcp.json
Agent docs: https://send21.io/llms.txt
OpenAPI: https://send21.io/swagger/v1/swagger.json
Site: https://send21.io

Connect

Point an MCP client at the remote server:

{
  "mcpServers": {
    "send21": {
      "url": "https://send21.io/mcp",
      "transport": "streamable-http",
      "headers": {
        "Authorization": "Bearer s21_YOUR_API_KEY"
      }
    }
  }
}

Auth: API key or OAuth sign-in.

• API key: create scoped keys at https://send21.io/api-keys (s21_…) and send them as above.

• OAuth sign-in: use https://send21.io/mcp/oauth with no headers; see Sign in instead of an API key below.

• Scopes such as drafts:write, drafts:read, webhooks:manage cannot move funds.

• tools/list and get_fee_schedule work without authentication.

Related MCP server: voulti-mcp

Sign in instead of an API key

Clients that support MCP sign-in (OAuth) can connect to https://send21.io/mcp/oauth with no key and no headers. The client opens send21 in your browser; you sign in, see what the app asks for, and approve. A connected app only ever uses receiving addresses you approved. It is listed under API keys as a connected app, where Disconnect ends it at once, and a connection nobody uses for 90 days ends by itself.

Claude Code

claude mcp add --transport http send21 https://send21.io/mcp/oauth
# then run /mcp in Claude Code and choose send21 to sign in
# (or, from your shell: claude mcp login send21)

Cursor (.cursor/mcp.json in your project, or ~/.cursor/mcp.json for all projects)

{
  "mcpServers": {
    "send21": {
      "url": "https://send21.io/mcp/oauth"
    }
  }
}

VS Code (.vscode/mcp.json)

{
  "servers": {
    "send21": {
      "type": "http",
      "url": "https://send21.io/mcp/oauth"
    }
  }
}

Any MCP client that supports OAuth: add https://send21.io/mcp/oauth as a remote (Streamable HTTP) MCP server with no headers, then sign in when the client asks.

Prefer an API key? It still works: use https://send21.io/mcp with Authorization: Bearer s21_..., a scoped key you create at https://send21.io/api-keys in your account. tools/list and get_fee_schedule work without either. Details: https://send21.io/docs/mcp

What the tools do

14 tools (see live tools/list): create_draft, get_draft, get_draft_status, list_draft_quotes, get_transaction_template, submit_lightning_proof, create_payment_request, get_payment_request, list_address_book, propose_receiving_address, get_account_status, create_account, get_rate, get_fee_schedule. Signing and broadcast stay in the user’s wallet.

Agents onboard themselves; humans approve where the money lands. An agent proposes a receiving address (propose_receiving_address) and the owner approves it after signing in, with a passkey or an authenticator code; no API key can approve an address, and any other address is refused (422 address_not_approved). An agent without a key can sign its owner up (create_account), but it cannot create anything until the owner takes the account over from an emailed link (403 owner_not_confirmed until then). Details: https://send21.io/docs/mcp

Brand

send21: crypto pay links and API for people and AI agents.
Contact: info@send21.io

License

MIT