# Impact Report: lnprototest – Strengthening the Lightning Network’s Foundation

The Lightning Network has transformed Bitcoin into a scalable, efficient payment system, enabling near-instant transactions with minimal fees. As a decentralized layer-two protocol, it relies on a diverse ecosystem of node implementations—such as LDK, Core Lightning, and others—to interoperate seamlessly. However, with rapid evolution and the introduction of new features, maintaining compliance with the protocol specifications (BOLTs and BLIPs) is an ongoing challenge. Non-compliance can lead to regressions, interoperability failures, or even forced channel closures, disrupting the network and eroding user trust.

## What is lnprototest?

lnprototest is a Python-based library designed to test Lightning Network implementations for protocol compliance. It enables developers to simulate node interactions, sending and receiving messages as defined in the BOLTs (Basis of Lightning Technology) and BLIPs (Bitcoin Lightning Improvement Proposals). By providing a standardized testing framework, lnprototest allows implementations to verify that their nodes adhere to the protocol, ensuring correct behavior across a range of scenarios—from basic connections to complex feature integrations.

A Lightning implementation integrates lnprototest by developing a custom Runner—a Python script that bridges the framework with the node’s deamon. This setup empowers developers to craft specific tests, execute them via tools like pytest, and validate their implementation’s performance.

## Why lnprototest Matters

The Lightning Network’s strength lies in its decentralization, but this also introduces complexity. As new features—like Onion Message DNS Resolution ([BLIP 32](https://github.com/lightning/blips/blob/master/blip-0032.md))—are proposed and implemented, the risk of errors or incompatibilities grows. lnprototest mitigates these risks by offering critical benefits:

- **Protocol Compliance**: It ensures nodes follow the latest specifications, catching deviations that could disrupt transactions or channel operations.
- **Regression Prevention**: By testing upgrades in a controlled environment, lnprototest prevents new features from breaking existing functionality.
- **Interoperability Assurance**: It verifies that different implementations can communicate and transact seamlessly, maintaining a unified network.

For example, a non-compliant node upgrading to a new version without proper testing could reject valid messages from peers, leading to channel closures and potential fund losses. lnprototest acts as a safety net, ensuring upgrades are smooth and the network remains stable as it scales.

## Evolution: From Monolithic to Modular

Thanks to open funds funding there was possible to work on the idea of lnprototest as a library and improve the usage of it. When lnprototest debuted in 2019, it was a monolithic application bundling all tests and runners in a single repository. While effective, this approach struggled to keep pace with the Lightning Network’s growth and the addition of optional features. Recognizing this, the project evolved into a modular library, available on [PyPI](https://pypi.org/project/lnprototest/), that implementations can import and customize.

This transformation brings significant advantages:

- **Custom Runners**: Developers can write their own Runner scripts, tailoring tests to their implementation’s unique features. For instance, the [Lampo project](https://github.com/vincenzopalazzo/lampo.rs/tree/main/tests/lnprototest) demonstrates this with its LampoRunner and a [ldk-runner under developemnt](https://github.com/Psycho-Pirate/ldk-sample) and https://github.com/rustyrussell/lnprototest/pull/131.
- **Out-of-Tree Testing**: Tests can reside in an implementation’s own codebase, reducing clutter in the main lnprototest repository and improving scalability.
- **Flexibility**: Teams can integrate lnprototest without overhauling their workflows, adapting it to their specific needs.

Other that implementing features, the focus of the work on lnprototest was also reseaching a better UX for the library and for the curius people this is the entry point for the reseach status https://github.com/rustyrussell/lnprototest/issues/105#issuecomment-2468755818

## Real-World Impact: Empowering the Ecosystem

lnprototest’s modular design delivers tangible benefits to the Lightning Network community:

- **Independent Validation**: Each implementation can develop and maintain its own tests, ensuring bespoke features are robustly implemented. For example, a simple test might verify that a node correctly handles an init message, as shown in a snippet from the Lampo project.
- **Interoperability Testing**: By sharing runners and test scenarios, implementations can perform cross-testing. If LDK releases its [BLIP 32](https://github.com/lightning/blips/blob/master/blip-0032.md) runner as a package, Core Lightning could use it to confirm compatibility, enhancing network cohesion.
- **Lowering Barriers**: New implementations can adopt lnprototest to validate compliance from day one, reducing the risk of introducing faulty nodes.

These capabilities strengthen the Lightning Network’s infrastructure, fostering collaboration and trust. As more teams integrate lnprototest, the network becomes more resilient, supporting broader adoption by users and businesses.

# Mantainer Quote

> Without the Open Sats grant awarded to lnprototest, the progress made in transforming lnprototest into a lightweight library that is easy to integrate, as well as the extensive research conducted over the past few months, might never have been possible. Currently, lnprototest is undergoing development in collaboration with LDK and other contributors who have received grants to work on integrating additional runners. We hope that, in the future, more individuals will be willing to contribute to improving weaker aspects of the library, particularly those stemming from limitations within the Python ecosystem.