libvaxis is a terminal user interface (TUI) library for Zig that provides both low-level terminal manipulation and a high-level declarative widget system (vxfw). The library does not rely on terminfo; instead it dynamically queries terminal capabilities via escape sequences, supporting modern features such as RGB color, kitty keyboard and graphics protocols, hyperlinks (OSC 8), bracketed paste, mouse shapes, system clipboard, notifications, synchronized output, and Unicode Core. The architecture comprises an event-driven loop (generic over event type) that reads from a platform-specific TTY abstraction, a state-machine parser for input sequences, double-buffered screen rendering with diff-based updates, and a widget tree with constraint-based layout, focus management, and event propagation (capture/target/bubble phases). Low-level components include the TTY abstraction (Posix, Windows, test stub), input parser, screen buffer, window sub-region handling, and image transmission via the kitty graphics protocol. The high-level vxfw framework offers composable widgets such as Button, TextInput, ListView, SplitView, Border, FlexRow/Column, ScrollView, Spinner, and more. Widgets receive draw context with min/max constraints and an arena allocator per frame, returning surfaces that may contain child surfaces. The library also includes an embedded terminal emulator widget (Terminal) that runs a child process in a PTY and renders its output as a virtual terminal. A stable C API is provided via `vaxis.h`, exposing parsing, screen manipulation, and runtime management without requiring Zig compilation. Cross-platform support covers macOS, Windows, Linux and BSD/Unix systems. The library is built with Zig 0.16.0 and depends on `zigimg` for image decoding and `uucode` for Unicode property data, both fetched as build dependencies.