Definition
The Lightning Dev Kit (LDK) is a complete Lightning Network implementation delivered as a software development kit rather than a standalone daemon. Built in Rust and stewarded by the LDK developers (a project supported by Spiral), it lets builders embed Lightning directly into their own applications with components they choose and assemble themselves.
SDK versus full node
Where implementations like LND, Core Lightning, and Eclair ship as a running node process, LDK provides the pieces — channel state machine, routing, peer-to-peer messaging — as libraries. A developer supplies their own persistence layer, networking, blockchain data source, and key management. This modularity is the point: it lets Lightning run inside resource-constrained environments such as mobile apps and hardware wallets, or scale up inside cloud services, without forcing one fixed architecture.
Where it is used
LDK exposes a native API across multiple languages, so it can be integrated on iOS, Android, web, HSMs, and server infrastructure. The project also offers higher-level packages such as LDK Node, a ready-made library for building self-custodial mobile wallets, and LDK Server for node-style deployments. Several large applications, including Cash App and Alby, have built on LDK.
LDK is one option among several ways to run Lightning; we describe it neutrally so builders can weigh an embeddable SDK against a full node daemon. For the daemon-style alternatives, see our entries on Core Lightning (CLN) and LND (Lightning Network Daemon).
In Simple Terms
The Lightning Dev Kit (LDK) is a complete Lightning Network implementation delivered as a software development kit rather than a standalone daemon. Built in Rust…