Building Lightning Apps: Open Source Tools for 2024

Cash App, one of the most downloaded finance apps in the United States, runs Lightning payments using the same open-source toolkit available to any developer with a GitHub account. That toolkit is the Lightning Dev Kit, and it's just one piece of a maturing ecosystem that's made building Lightning applications dramatically more accessible in 2024.

The gap between "I want to build a Lightning app" and actually shipping one has never been smaller. Here's what's worth knowing about the current state of the tools.

The Core Node Implementations

Three open-source Lightning node implementations dominate the landscape, each with distinct tradeoffs.

LND (Lightning Network Daemon) remains the most widely deployed implementation. Written in Go, it handles channel creation, pathfinding, and payment routing with a battle-tested codebase that powers much of the network's infrastructure. If you need something that "just works" for running a production node, LND is the safe choice.

Core Lightning (formerly c-lightning) takes a different approach. Built in C with a focus on spec compliance and performance, it's leaner and more modular. Its plugin architecture lets you extend functionality without touching core code. Developers who value flexibility and want to build custom tooling often prefer it.

LDK (Lightning Development Kit) isn't a node implementation in the traditional sense. It's a modular SDK based on rust-lightning that lets you build Lightning functionality directly into your application. BlueWallet and Cash App both use it. The key difference: instead of running a separate node process and talking to it via API, you integrate Lightning as a library.

LDK supports bindings for Rust, Swift, Java, Kotlin, and JavaScript/WASM, which means you can build non-custodial mobile wallets that run real Lightning nodes on users' phones. Recent 2024 updates added Phantom Node support for receiving payments across multiple nodes and improved client-side pathfinding.

For teams building mobile wallets, exchanges, or hardware devices, LDK's ability to plug into existing databases and networking stacks makes it more practical than standalone node implementations that demand their own isolated environments.

Testing Without Touching Mainnet

The most praised tool among Lightning developers for local testing is Polar. With one click, you can spin up a complete regtest Lightning network on your laptop, including nodes from LND, Core Lightning, Eclair, and Bitcoin Core. You can open channels, send payments, and test failure scenarios without risking real funds or waiting for block confirmations.

Polar's visual interface shows your test network as a graph, making it easy to see channel states and balances. For developers new to Lightning, this alone demystifies how the protocol actually works.

For larger-scale testing, Scaling Lightning provides a Kubernetes-based toolkit that can simulate networks with many nodes. This matters when you need to test how your application behaves under realistic network conditions, not just with three nodes on your laptop.

The create-ln-app template combines ReactJS with Polar to give you a working Lightning app scaffold in minutes. It's a reasonable starting point if you want to experiment before committing to a larger project.

Supporting Tools Worth Knowing

Balance of Satoshis (BOS) has become essential for LND node operators managing liquidity. It handles channel rebalancing, fee management, and provides better visibility into node performance than LND's default tooling.

ThunderHub offers a web-based interface for node management, useful when you need to monitor or operate nodes remotely.

WebLN provides browser standards for Lightning app communication, similar to what Web3 libraries do for Ethereum. If you're building web-based Lightning experiences, this is how users connect their wallets to your application.

The curated lists on GitHub (particularly setlife-network/awesome-lightning-network) remain the best way to discover new tools as they emerge.

Where to Actually Learn This Stuff

Documentation and GitHub repos only take you so far. For hands-on learning with experienced Lightning developers, Bitcoin++ runs focused technical workshops on Lightning, protocol engineering, and scaling solutions. The format is explicitly designed for engineers who want to work through code, not passively watch presentations. It's not beginner-friendly by design, but if you already have a technical background and want to go deep on Lightning internals, the workshop environment beats self-study.

Tradeoffs to Consider

The tooling has improved, but Lightning development still involves meaningful tradeoffs.

LND offers stability and ecosystem support but less flexibility for custom integrations. Core Lightning gives you modularity but a smaller plugin ecosystem. LDK provides maximum control but requires you to handle more yourself, including persistence, networking, and blockchain data sourcing.

For testing, Polar is perfect for local development but doesn't simulate network latency, gossip delays, or adversarial peers. Scaling Lightning addresses some of this but requires Kubernetes expertise.

Mobile non-custodial Lightning remains genuinely hard. LDK makes it possible, but you're still dealing with background sync challenges, battery constraints, and the fundamental difficulty of receiving payments when offline.

Looking Forward

The 2024 Lightning ecosystem is substantially more accessible than even two years ago. You can go from zero to a working Lightning app on regtest in an afternoon using Polar and LDK. Whether that app becomes production-ready depends on understanding the tradeoffs above and choosing tools that match your specific constraints.

The best approach is probably to start with Polar for experimentation, pick a node implementation or SDK based on your deployment target, and lean on the curated community lists when you hit edges cases. The tooling is mature enough that the limiting factor is usually understanding Lightning's mechanics, not the quality of available libraries.

That understanding takes time, but the tools are no longer the bottleneck.