# Breez SDK - *Liquid*

## **Overview**

The Breez SDK provides developers with a end-to-end solution for integrating self-custodial Lightning payments into their apps and services. It eliminates the need for third-parties, simplifies the complexities of Bitcoin and Lightning, and enables seamless onboarding for billions of users to the future of peer-to-peer payments.

To provide the best experience for their end-users, developers can choose between the following implementations:

- [Breez SDK - *Liquid*](https://sdk-doc-liquid.breez.technology/)
- [Breez SDK - *Greenlight*](https://sdk-doc.breez.technology/)

**The Breez SDK is free for developers.**

## **What Is the *Liquid* Implementation?**

The *Liquid* implementation is a nodeless Lightning integration. It offers a self-custodial, end-to-end solution for integrating Lightning payments, utilizing the Liquid Network with on-chain interoperability and third-party fiat on-ramps.

**Core Functions**

- **Sending payments** *via protocols such as: bolt11, lnurl-pay, lightning address, btc address.*
- **Receiving payments** *via protocols such as: bolt11, lnurl-withdraw, btc address.*
- **Interacting with a wallet** *e.g. balance, max allow to pay, max allow to receive, on-chain balance.*

**Key Features**

- [x]  On-chain interoperability
- [x]  LNURL functionality
- [x]  Multi-app support
- [x]  Multi-device support
- [x]  Real-time state backup
- [x]  Keys are only held by users
- [x]  Fiat on-ramps
- [x]  Open-source

## Getting Started 

Head over to the [Breez SDK - Liquid documentation](https://sdk-doc-liquid.breez.technology/) to start implementing Lightning in your app.

## **API**

API documentation is [here](https://breez.github.io/breez-sdk-liquid/breez_sdk_liquid/).

## **Command Line**

The [Breez SDK - *Liquid* cli](https://github.com/breez/breez-sdk-liquid/tree/main/cli) is a command line client that allows you to interact with and test the functionality of the SDK.

## **Support**

Have a question for the team? Join our [Telegram channel](https://t.me/breezsdk) or email us at [contact@breez.technology](mailto:contact@breez.technology) 

## How Does the *Liquid* Implementation Work?

The *Liquid* implementation uses submarine swaps and reverse submarine swaps to send and receive payments, enabling funds to move frictionlessly between the Lightning Network and the Liquid sidechain.

![Breez SDK - Liquid](https://github.com/breez/breez-sdk-liquid-docs/raw/main/src/images/BreezSDK_Liquid.png)

When sending a payment the SDK performs a submarine swap, converting L-BTC from a user’s Liquid wallet into sats on the Lightning Network, and sends them to the recipient.

When receiving a payment, the SDK performs a reverse submarine swap, converting incoming sats into L-BTC, and then deposits them in the user’s Liquid wallet.

## **Build & Test**

- **cli**:  Contains the Rust command line interface client for the SDK - *Liquid*.
- **lib**: Contains the root Rust cargo workspace.
    - **bindings**: The ffi bindings for Kotlin, Flutter, Python, React Native, and Swift.
    - **core**: The core SDK - *Liquid* rust library.
- **packages**: Contains the plugin packages for Dart, Flutter, and React Native.

Within each sub-project readme, there are instructions on how to build, test, and run.

## **SDK Development Roadmap**

- [x]  Send/Receive Lightning payments
- [x]  CLI Interface
- [x]  Foreign languages bindings
- [x]  Export/Import SDK data
- [x]  Pay BTC on-chain
- [x]  Receive via on-chain address
- [x]  LNURL-Pay
- [x]  LNURL-Withdraw
- [x]  Send to a Lightning address
- [ ]  Receive via Lightning address
- [ ]  Real-time sync
- [ ]  Webhook for receiving payments
- [ ]  Offline receive via notifications
- [ ]  Offline swaps via notifications