# Developer docs

Everything you need to create payment requests and drafts from your own code or from an AI agent. send21 prepares payment instructions; the payer always signs in their own wallet, and send21 never holds keys or funds.

## Start here

- [API quickstart](https://send21.io/docs/quickstart): API keys, your first payment request and draft, status and idempotency.
- [Webhooks](https://send21.io/docs/webhooks): events, payloads, retries and signature checks.
- [MCP server](https://send21.io/docs/mcp): connect an AI agent over the Model Context Protocol.
- [Currencies and networks](https://send21.io/docs/currencies): which assets each network carries, decimals and confirmations.
- [Lightning](https://send21.io/docs/lightning): pay links and drafts that confirm through the receiver's Lightning address.

## Machine-readable references

- OpenAPI 3 specification: [/openapi.json](https://send21.io/openapi.json), browsable at [/swagger](https://send21.io/swagger).
- Overview for language models: [/llms.txt](https://send21.io/llms.txt), with every doc in one file at [/llms-full.txt](https://send21.io/llms-full.txt).
- Every docs page is also available as Markdown: add `.md` to the address, for example [/docs/webhooks.md](https://send21.io/docs/webhooks.md).

## Try it without an account

The [testnet demo](https://send21.io/demo) runs the whole flow on test networks with free test coins: a draft, a QR payment from your own wallet, and an on-chain confirmation. No account and no email.

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Source: https://send21.io/docs