Lightning Loop is a non-custodial service offered by Lightning Labs to bridge on-chain and off-chain Bitcoin using submarine swaps. This repository is home to the Loop client and depends on the Lightning Network daemon lnd. All of lnd’s supported chain backends are fully supported when using the Loop client: Neutrino, Bitcoin Core, and btcd.
In the current iteration of the Loop software, only off-chain to on-chain swaps are supported, where the Loop client sends funds off-chain in exchange for the funds back on-chain. This is called a Loop Out.
The service can be used in various situations:
- Acquiring inbound channel liquidity from arbitrary nodes on the Lightning network
- Depositing funds to a Bitcoin on-chain address without closing active channels
- Paying to on-chain fallback addresses in the case of insufficient route liquidity
Future iterations of the Loop software will also allow on-chain to off-chain swaps. These swaps can be useful for additional use-cases:
- Refilling depleted channels with funds from cold-wallets or exchange withdrawals
- Servicing off-chain Lightning withdrawals using on-chain payments, with no funds in channels required
- As a failsafe payment method that can be used when channel liquidity along a route is insufficient
Development and Support
The Loop client is current in an early beta state, and offers a simple command line application. Future APIs will be added to support implementation or use of the Loop service.
Setup and Install
LND and the loop client are using Go modules. Make sure that the
env variable is set to
In order to execute a swap, LND will need to be rebuilt on master with sub servers enabled.
Make sure that you are using the
master branch of lnd. You can get this by
git cloning the repository
git clone https://github.com/lightningnetwork/lnd.git
Once the lnd repository is cloned, it will need to be built with special build tags that enable the swap. This enables the required lnd rpc services.
cd lnd make install tags="signrpc walletrpc chainrpc invoicesrpc"
Check to see if you have already installed lnd. If you have, you will need to
.macaroon files from your lnd directory.
Do not delete any other files other than the
// Example on Linux to see macaroons in the default directory: ls ~/.lnd/data/chain/bitcoin/mainnet
This should show no
.macaroon files. If it does? Stop lnd, delete macaroons,
Now delete the .macaroon files and restart lnd. (don't delete any other files)
After lnd is installed, you will need to clone the Lightning Loop repo and install the command line interface and swap client service.
git clone https://github.com/lightninglabs/loop.git cd loop/cmd go install ./...
Execute a Swap
After you have lnd and the Loop client installed, you can execute a Loop swap.
The Loop client needs its own short-lived daemon which will deal with the swaps in progress.
Command to start
loopd // Or if you want to do everything in the same terminal and background loopd loopd & // For testnet mode, you'll need to specify the network as mainnet is the default: loopd --network=testnet
loopd attempts to connect to the lnd instance running on
localhost:10009 and reads the macaroon and tls certificate from
This can be altered using command line flags. See
loopd only listens on localhost and uses an unencrypted and unauthenticated
Now that loopd is running, you can initiate a simple Loop Out. This will pay out Lightning off-chain funds and you will receive Bitcoin on-chain funds in return. There will be some chain and routing fees associated with this swap.
loop out <amt_in_satoshis>
This will take some time, as it requires an on-chain confirmation. When the
swap is initiated successfully,
loopd will see the process through.
To query in-flight swap statuses, run
loopd is terminated (or killed) for whatever reason, it will pickup
pending swaps after a restart.
Information about pending swaps is stored persistently in the swap database.
Its location is
Multiple Simultaneous Swaps
It is possible to execute multiple swaps simultaneously. Just keep loopd running.