![bark: Ark on bitcoin](assets/bark-header-white.jpg)

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<h1>Bark: Ark on bitcoin</h1>
<p>Fast, low-cost, self-custodial payments on bitcoin.</p>
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<p align="center">
  <br />
  <a href="https://docs.second.tech">Docs</a> ·
  <a href="https://gitlab.com/ark-bitcoin/bark/issues">Issues</a> ·
  <a href="https://second.tech">Website</a> ·
  <a href="https://blog.second.tech">Blog</a> ·
  <a href="https://www.youtube.com/@2ndbtc">YouTube</a>
</p>

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[![Release](https://img.shields.io/gitlab/pipeline-status/ark-bitcoin/bark?branch=master&gitlab_url=https%3A%2F%2Fgitlab.com)](https://gitlab.com/ark-bitcoin/bark/tags)
[![License](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
[![PRs welcome](https://img.shields.io/badge/PRs-welcome-brightgreen?logo=git)](CONTRIBUTING.md)
[![Community](https://img.shields.io/badge/community-forum-blue?logo=discourse)](https://community.second.tech)

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Bark is an implementation of the Ark protocol on bitcoin, led by [Second](https://second.tech). The Ark protocol is a bitcoin layer 2 for making fast, low-cost, self-custodial payments at scale. Ark uses a client-server model to enable users to transact off-chain while still being able to "exit" their balances on-chain at any time.

The project consists of:

- The Ark wallet: **bark**
- The Ark server: **captaind**
- A set of libraries containing all protocol primitives

## Get started

- [**Make your first Ark transactions**](https://docs.second.tech/getting-started/): Step-by-step guide to set up a CLI wallet, get sats from [our faucet](https://signet.2nd.dev), and buy some treats from [our test store](https://signet.2nd.dev/store).
- [**Compile from source**](https://docs.second.tech/getting-started/optional/compile-from-source/)
- [**Set up an Ark server**](https://docs.second.tech/run-ark-server/): For patient folks looking to do more in-depth testing!

## What if I don't speak Rust?

No Rust, no problem!

**barkd** is an Ark wallet that runs as a daemon and exposes a REST API over HTTP. It's well suited for power users and great for automation—think web shops, Telegram/Discord bots, and similar use cases. The [barkd-clients repository](https://gitlab.com/ark-bitcoin/barkd-clients) provides clients in TypeScript and C#.

**uniffi-bindings** are the better choice if you're building a native desktop or mobile application. The bindings are available in the [bark-ffi repository](https://gitlab.com/ark-bitcoin/bark-ffi). These are still experimental, but stabilizing quickly.

## Why Ark?

As bitcoin adoption grows, on-chain fees spike during busy periods, making everyday transactions impractical. While Lightning has been revolutionary for bitcoin scaling, it's beginning to show its limitations-channel management and liquidity requirements create complexity for developers and users.

Ark offers a complementary scaling solution that simplifies bitcoin self-custody:

🏃‍♂️ **Smooth onboarding**: No channels to open, no on-chain setup required-create a wallet and start transacting  
🤌 **Simplified UX**: Send and receive without managing channels, liquidity, or routing  
🌐 **Universal payments**: Send Ark, Lightning, and on-chain payments from a single off-chain balance  
🔌 **Easier integration**: Client-server architecture reduces complexity compared to P2P protocols  
💸 **Lower costs**: Instant payments at a fraction of on-chain fees  
🔒 **Self-custodial**: Users maintain full control of their funds at all times

Perfect for users who want self-custody without the hassle, and developers who want to build bitcoin apps without the complexity.

[Learn more about Ark's benefits →](https://second.tech)

## How does Ark work?

The Ark protocol enables multiple users to share control of a single bitcoin UTXO through a tree of pre-signed, off-chain transactions. This allows instant, off-chain payments while maintaining self-custody-users can always withdraw their bitcoin either cooperatively with the Ark server or unilaterally on-chain.

For a detailed technical explanation, see our [protocol documentation](https://second.tech/docs/learn/intro).

![An example of an Ark transaction tree from a refresh](assets/tx-tree-refresh.jpg)
_A transaction tree showing how Ark enables multiple users to share control of a single UTXO through pre-signed transactions._

## Minimum supported Rust version (MSRV)

Most of our crates do not yet specify a MSRV, but we will commit to one once we make an official release.

The `ark-lib` crate (and by extension the `bark-bitcoin-ext` crate) have a MSRV of v1.74.0.

## Contributing

Thinking of opening a pull request? See our [contribution guide](CONTRIBUTING.md) for dependencies, style guidelines, and code hygiene expectations.

### Security

Please report any vulnerability or any bug that could potentially affect the
security of users' funds by e-mail to [`security@second.tech`](mailto:security@second.tech).

You may use the following PGP keys to encrypt your e-mail:

- `8CC974D9CFD034DCEED213B02A57E0A610D7F19C` (Steven Roose)
- `011E7F59B45397C4654D81298F44B2DD98E18528` (Erik De Smedt)

Both keys can be found on the [keys.openpgp.org](https://keys.openpgp.org/) keyserver.


## Questions or issues

If you run into any issues at all, let us know:

- [Community forum](https://community.second.tech)
- [Community chat](https://chat.second.tech)
- [Issue tracker](https://gitlab.com/ark-bitcoin/bark/issues)

## Security policy and responsible disclosure

**The Ark protocol code is experimental and must not be used in production.**

If you happen to find a vulnerability we invite you to [file a public issue](https://gitlab.com/ark-bitcoin/bark/issues/new).

## License

Released under the **MIT** license-see the [LICENSE](LICENSE) file for details.