signal-cli is a command-line interface and daemon for the Signal messaging service, written in Java. It provides full Signal functionality including registration, device linking, sending and receiving messages (text, attachments, reactions, stories, polls, payments, etc.), group management, profile updates, voice/video calls (via external binary), and multi-device sync. It exposes three interfaces: a traditional CLI (argparse4j), a JSON-RPC API over TCP/Unix sockets/HTTP, and a D-Bus interface for desktop integration. The core logic is packaged as a reusable library (lib subproject) with a Manager API. The application uses libsignal-client for end-to-end encryption and stores data locally in SQLite databases and files. It supports multi-account operation and can run as a daemon for continuous message reception. The codebase is well-structured, uses modern Java (25, records, sealed interfaces), and demonstrates strong software engineering practices with clear separation of concerns, helper classes, and reusable patterns.