An ergonomic, immediate-mode Terminal User Interface (TUI) library for Nim.

TaTUÍ helps you build rich, flicker-free terminal apps by describing your UI as a pure function of your application state. You rebuild the interface every tick; TaTUÍ figures out the minimal set of cells that actually changed and updates only those.

Status: v1 core is implemented and tested — core buffer/diff, ANSI + test backends, constraint layout, the terminal tick loop, an event decoder, and the widget set (Block, Paragraph, List, Table, Tabs, Clear, Gauge, Sparkline, BarChart, Scrollbar, Chart).

• Immediate mode, no flicker. Draw your whole UI each frame from current state. A retained cell buffer is diffed under the hood, so only real changes are written to the terminal.
• Constraint-based layout. No absolute coordinates — split areas with Length, Percentage, Ratio, Min, Max, and Fill, and let the layout engine do the arithmetic.
• Backend-agnostic. Drawing logic never touches the OS directly; everything flows through a small Backend concept, which also makes rendering fully testable without a real terminal.
• Built for Nim. Value types and seq-backed buffers, an allocation-free steady-state render path, and --mm:orc throughout.

1. Double buffering + diffing — widgets write into an in-memory Buffer; TaTUÍ diffs it against the previous frame and emits only the deltas.
2. Backend agnosticism — spatial and drawing logic knows nothing about the terminal; output goes through the Backend concept.
3. Constraint-based layout — Rects are split by constraints, not fixed positions.

Linux and macOS, via pure ANSI escape sequences and termios raw mode. (Windows is not targeted in v1.)

nimble install tatui

Requires Nim ≥ 2.0.

import tatui

var term = newTerminal(newAnsiBackend())
term.setup()
defer: term.restore()

term.draw proc(f: var Frame) =
  let chunks = f.area.split(Vertical, @[length(3), fill(1)])
  f.renderWidget(initBlock(title = " TaTUÍ ", borders = AllBorders), chunks[0])
  f.renderWidget(paragraph("Hello, terminal!"), chunks[1])

See runnable examples in examples/: examples/hello.nim (interactive) and examples/demo.nim (renders a dashboard to text, no TTY required).

• src/tatui/ — library source (core, layout, backend, terminal, event, widgets).
• specs/ — behavior specs written before the code that implements them.
• docs/adr/ — architecture decision records.
• docs/reference/ — the ratatui parity map and trimmed terminal references.

TaTUÍ is spec-first: adjust the spec in specs/, add a failing test, then implement. See AGENTS.md for the reasoning loop and Definition of Done, and .github/copilot-instructions.md for the architectural invariants. Please be kind and constructive in issues and reviews — everyone here is learning and building together. 💚

TaTUÍ stands on the shoulders of ratatui, the wonderful Rust TUI library whose architecture — double buffering, backend abstraction, and constraint-based layout — is the direct inspiration for this project. Huge thanks to the ratatui maintainers and community for their thoughtful design and generous open-source work. If you write Rust, go build something with ratatui. 🐁❤️

We also thank the Nim community for a language that makes this kind of library a joy to write.

MIT. See LICENSE.