ExRatatui

Elixir bindings for the Rust ratatui terminal UI library, via Rustler NIFs.

Build rich terminal UIs in Elixir with ratatui's layout engine, widget library, and styling system — without blocking the BEAM.

Features

• 16 built-in widgets (and counting!): Paragraph, Block, List, Table, Gauge, LineGauge, Tabs, Scrollbar, Checkbox, TextInput, Clear, Markdown, Textarea, Throbber, Popup, WidgetList
• Constraint-based layout engine (percentage, length, min, max, ratio)
• Non-blocking keyboard, mouse, and resize event polling
• OTP-supervised TUI apps via ExRatatui.App behaviour with LiveView-inspired callbacks
• Built-in SSH transport — serve any ExRatatui.App as a remote TUI, standalone or under nerves_ssh
• Full color support: named, RGB, and 256-color indexed
• Text modifiers: bold, italic, underlined, and more
• Headless test backend for CI-friendly rendering verification
• Precompiled NIF binaries — no Rust toolchain needed
• Runs on BEAM's DirtyIo scheduler — never blocks your processes

Examples

Try an example over SSH

Two of the examples ship with a one-flag switch to serve them over SSH instead of your local terminal — great for testing multi-client behaviour or previewing Nerves-style remote TUIs.

system_monitor.exs (standalone script, --ssh flag):

mix run --no-halt examples/system_monitor.exs --ssh
# in another terminal:
ssh demo@localhost -p 2222      # password: demo

task_manager/ (Mix project, TASK_MANAGER_SSH env var):

cd examples/task_manager
mix deps.get && mix ecto.setup   # first time only
TASK_MANAGER_SSH=1 mix run --no-halt
# in one or more other terminals:
ssh demo@localhost -p 2222      # password: demo

Every SSH client for task_manager gets its own isolated TUI session but they all read and write the same SQLite database — add a task in one window, see it appear in the others. See the SSH transport guide for how this all works.

Built with ExRatatui

• ash_tui — Interactive terminal explorer for Ash domains, resources, attributes, actions, and more.
• nerves_ex_ratatui_example — Example Nerves project demonstrating ExRatatui on embedded hardware, with a system monitor and LED control TUI.
• phoenix_ex_ratatui_example — Example Phoenix 1.8 project demonstrating an admin TUI served over SSH alongside a public LiveView, sharing PubSub between the browser and the terminal so messages posted in the web app stream live into every connected SSH session.

Installation

Add ex_ratatui to your dependencies in mix.exs:

def deps do
  [
    {:ex_ratatui, "~> 0.6"}
  ]
end

Then fetch and compile:

mix deps.get && mix compile

A precompiled NIF binary for your platform will be downloaded automatically.

Prerequisites

• Elixir 1.17+

Precompiled NIF binaries are available for Linux (x86_64, aarch64, armv6/hf, riscv64), macOS (x86_64, aarch64), and Windows (x86_64). No Rust toolchain needed.

To compile from source instead, install the Rust toolchain and set:

export EX_RATATUI_BUILD=true

Quick Start

alias ExRatatui.Layout.Rect
alias ExRatatui.Style
alias ExRatatui.Widgets.{Block, Paragraph}

ExRatatui.run(fn terminal ->
  {w, h} = ExRatatui.terminal_size()

  paragraph = %Paragraph{
    text: "Hello from ExRatatui!\n\nPress any key to exit.",
    style: %Style{fg: :green, modifiers: [:bold]},
    alignment: :center,
    block: %Block{
      title: " Hello World ",
      borders: [:all],
      border_type: :rounded,
      border_style: %Style{fg: :cyan}
    }
  }

  ExRatatui.draw(terminal, [{paragraph, %Rect{x: 0, y: 0, width: w, height: h}}])

  # Wait for a keypress, then exit
  ExRatatui.poll_event(60_000)
end)

Try the examples for more, e.g. mix run examples/hello_world.exs.

OTP App Behaviour

For supervised TUI applications, use the ExRatatui.App behaviour — a LiveView-inspired callback interface that manages the terminal lifecycle under OTP:

defmodule MyApp.TUI do
  use ExRatatui.App

  @impl true
  def mount(_opts) do
    {:ok, %{count: 0}}
  end

  @impl true
  def render(state, frame) do
    alias ExRatatui.Widgets.Paragraph
    alias ExRatatui.Layout.Rect

    widget = %Paragraph{text: "Count: #{state.count}"}
    rect = %Rect{x: 0, y: 0, width: frame.width, height: frame.height}
    [{widget, rect}]
  end

  @impl true
  def handle_event(%ExRatatui.Event.Key{code: "q"}, state) do
    {:stop, state}
  end

  def handle_event(%ExRatatui.Event.Key{code: "up"}, state) do
    {:noreply, %{state | count: state.count + 1}}
  end

  def handle_event(_event, state) do
    {:noreply, state}
  end
end

Add it to your supervision tree:

children = [{MyApp.TUI, []}]
Supervisor.start_link(children, strategy: :one_for_one)

Callbacks

See the task_manager example for a full Ecto-backed app using this behaviour.

Running Over SSH

Any ExRatatui.App module can also be served as a remote TUI over SSH. The transport is pure OTP :ssh — no extra processes, no external sshd, no native code beyond what ExRatatui already uses. See the Running TUIs over SSH guide for the full options reference, auth setup, and troubleshooting tips.

Drop ExRatatui.SSH.Daemon into your supervision tree:

children = [
  {ExRatatui.SSH.Daemon,
   mod: MyApp.TUI,
   port: 2222,
   system_dir: ~c"/etc/ex_ratatui/host_keys",
   auth_methods: ~c"password",
   user_passwords: [{~c"admin", ~c"s3cret"}]}
]

Supervisor.start_link(children, strategy: :one_for_one)

Then connect from another machine:

ssh admin@your-host -p 2222

Each client gets its own isolated session with its own state and screen size. A single daemon can serve many concurrent TUIs.

See phoenix_ex_ratatui_example for a complete Phoenix 1.8 application doing exactly this — an admin TUI served over SSH alongside a public LiveView, sharing PubSub between the browser and the terminal.

Nerves + nerves_ssh

If you're already running nerves_ssh on a Nerves device, register ExRatatui.SSH as a subsystem instead of standing up a second daemon:

config :nerves_ssh,
  subsystems: [
    :ssh_sftpd.subsystem_spec(cwd: ~c"/"),
    ExRatatui.SSH.subsystem(MyApp.TUI)
  ]

Connect with:

ssh nerves.local -s Elixir.MyApp.TUI

See nerves_ex_ratatui_example for a complete Nerves firmware that wires two TUIs (a system monitor and an LED control app) into a nerves_ssh daemon and runs them on a Raspberry Pi.

How It Works

ExRatatui bridges Elixir and Rust through Rustler NIFs (Native Implemented Functions):

Elixir structs -> encode to maps -> Rust NIF -> decode to ratatui types -> render to terminal
Terminal events -> Rust NIF (DirtyIo) -> encode to tuples -> Elixir Event structs

• Rendering: Elixir widget structs are encoded as string-keyed maps, passed across the NIF boundary, and decoded into ratatui widget types for rendering.
• Events: The poll_event NIF runs on BEAM's DirtyIo scheduler, so event polling never blocks normal Elixir processes.
• Terminal state: Each process holds its own terminal reference via Rust ResourceArc, supporting two backends — a real crossterm terminal and a headless test backend for CI. The terminal is automatically restored when the reference is garbage collected.
• Layout: Ratatui's constraint-based layout engine is exposed directly, computing split rectangles on the Rust side and returning them as Elixir tuples.

Precompiled binaries are provided via rustler_precompiled so users don't need the Rust toolchain.

Widgets

Paragraph

Text display with alignment, wrapping, and scrolling.

%Paragraph{
  text: "Hello, world!\nSecond line.",
  style: %Style{fg: :cyan, modifiers: [:bold]},
  alignment: :center,
  wrap: true
}

Block

Container with borders and title. Can wrap any other widget via the :block field.

%Block{
  title: "My Panel",
  borders: [:all],
  border_type: :rounded,
  border_style: %Style{fg: :blue}
}

# Compose with other widgets:
%Paragraph{
  text: "Inside a box",
  block: %Block{title: "Title", borders: [:all]}
}

List

Selectable list with highlight support.

%List{
  items: ["Elixir", "Rust", "Haskell"],
  highlight_style: %Style{fg: :yellow, modifiers: [:bold]},
  highlight_symbol: " > ",
  selected: 0,
  block: %Block{title: " Languages ", borders: [:all]}
}

Table

Table with headers, rows, and column width constraints.

%Table{
  rows: [["Alice", "30"], ["Bob", "25"]],
  header: ["Name", "Age"],
  widths: [{:length, 15}, {:length, 10}],
  highlight_style: %Style{fg: :yellow},
  selected: 0
}

Gauge

Progress bar.

%Gauge{
  ratio: 0.75,
  label: "75%",
  gauge_style: %Style{fg: :green}
}

LineGauge

Thin single-line progress bar with separate filled/unfilled styles.

%LineGauge{
  ratio: 0.6,
  label: "60%",
  filled_style: %Style{fg: :green},
  unfilled_style: %Style{fg: :dark_gray}
}

Tabs

Tab bar for switching between views.

%Tabs{
  titles: ["Home", "Settings", "Help"],
  selected: 0,
  highlight_style: %Style{fg: :cyan, modifiers: [:bold]},
  divider: " | ",
  block: %Block{borders: [:all]}
}

Scrollbar

Scroll position indicator for long content. Supports vertical and horizontal orientations.

%Scrollbar{
  content_length: 100,
  position: 25,
  viewport_content_length: 10,
  orientation: :vertical_right,
  thumb_style: %Style{fg: :cyan}
}

Checkbox

Boolean toggle with customizable symbols.

%Checkbox{
  label: "Enable notifications",
  checked: true,
  checked_style: %Style{fg: :green},
  checked_symbol: "✓",
  unchecked_symbol: "✗"
}

TextInput

Single-line text input with cursor navigation and viewport scrolling. This is a stateful widget — its state lives in Rust via ResourceArc.

# Create state (once, e.g. in mount/1)
state = ExRatatui.text_input_new()

# Forward key events
ExRatatui.text_input_handle_key(state, "h")
ExRatatui.text_input_handle_key(state, "i")

# Read/set value
ExRatatui.text_input_get_value(state)  #=> "hi"
ExRatatui.text_input_set_value(state, "hello")

# Render
%TextInput{
  state: state,
  style: %Style{fg: :white},
  cursor_style: %Style{fg: :black, bg: :white},
  placeholder: "Type here...",
  placeholder_style: %Style{fg: :dark_gray},
  block: %Block{title: "Search", borders: [:all], border_type: :rounded}
}

Clear

Resets all cells in its area to empty (space) characters. Useful for rendering overlays on top of existing content.

%Clear{}

Markdown

Renders markdown with syntax-highlighted code blocks. Powered by tui-markdown (pulldown-cmark + syntect). Supports headings, bold, italic, inline code, fenced code blocks, bullet lists, links, and horizontal rules.

%Markdown{
  content: "# Hello\n\nSome **bold** text and `inline code`.\n\n```elixir\nIO.puts(\"hi\")\n```",
  wrap: true,
  block: %Block{title: "Response", borders: [:all]}
}

Textarea

Multiline text editor with undo/redo, cursor movement, and Emacs-style shortcuts. This is a stateful widget — state lives in Rust via ResourceArc.

# Create state (once, e.g. in mount/1)
state = ExRatatui.textarea_new()

# Forward key events (with modifier support)
ExRatatui.textarea_handle_key(state, "h", [])
ExRatatui.textarea_handle_key(state, "enter", [])
ExRatatui.textarea_handle_key(state, "w", ["ctrl"])  # delete word backward

# Read value
ExRatatui.textarea_get_value(state)  #=> "h\n"

# Render
%Textarea{
  state: state,
  placeholder: "Type your message...",
  placeholder_style: %Style{fg: :dark_gray},
  block: %Block{title: "Message", borders: [:all], border_type: :rounded}
}

Throbber

Loading spinner that animates through symbol sets. The caller controls animation by incrementing :step on each tick.

%Throbber{
  label: "Loading...",
  step: state.tick,
  throbber_set: :braille,
  throbber_style: %Style{fg: :cyan},
  block: %Block{title: "Status", borders: [:all]}
}

Available sets: :braille, :dots, :ascii, :vertical_block, :horizontal_block, :arrow, :clock, :box_drawing, :quadrant_block, :white_square, :white_circle, :black_circle.

Popup

Centered modal overlay. Renders any widget centered over the parent area, clearing the background underneath. Useful for dialogs, confirmations, and command palettes.

%Popup{
  content: %Paragraph{text: "Are you sure?"},
  block: %Block{title: "Confirm", borders: [:all], border_type: :rounded},
  percent_width: 50,
  percent_height: 30
}

WidgetList

Vertical list of heterogeneous widgets with optional selection and scrolling. Each item is a {widget, height} tuple. Ideal for chat message histories where items have different heights.

%WidgetList{
  items: [
    {%Paragraph{text: "User: Hello!"}, 1},
    {%Markdown{content: "**Bot:** Hi there!\n\nHow can I help?"}, 4},
    {%Paragraph{text: "User: What is Elixir?"}, 1}
  ],
  selected: 1,
  highlight_style: %Style{fg: :yellow},
  scroll_offset: 0,
  block: %Block{title: "Chat", borders: [:all]}
}

Layout

Split areas into sub-regions using constraints:

alias ExRatatui.Layout
alias ExRatatui.Layout.Rect

area = %Rect{x: 0, y: 0, width: 80, height: 24}

# Three-row layout: header, body, footer
[header, body, footer] = Layout.split(area, :vertical, [
  {:length, 3},
  {:min, 0},
  {:length, 1}
])

# Split body into sidebar + main
[sidebar, main] = Layout.split(body, :horizontal, [
  {:percentage, 30},
  {:percentage, 70}
])

Constraint types: {:percentage, n}, {:length, n}, {:min, n}, {:max, n}, {:ratio, num, den}.

Events

Poll for keyboard, mouse, and resize events without blocking the BEAM:

case ExRatatui.poll_event(100) do
  %Event.Key{code: "q", kind: "press"} ->
    :quit

  %Event.Key{code: "up", kind: "press"} ->
    :move_up

  %Event.Key{code: "j", kind: "press", modifiers: ["ctrl"]} ->
    :ctrl_j

  %Event.Resize{width: w, height: h} ->
    {:resized, w, h}

  nil ->
    :timeout
end

Styles

# Named colors
%Style{fg: :green, bg: :black}

# RGB
%Style{fg: {:rgb, 255, 100, 0}}

# 256-color indexed
%Style{fg: {:indexed, 42}}

# Modifiers
%Style{modifiers: [:bold, :dim, :italic, :underlined, :crossed_out, :reversed]}

Testing

ExRatatui includes a headless test backend for CI-friendly rendering verification. Each test terminal is independent, enabling async: true tests:

test "renders a paragraph" do
  terminal = ExRatatui.init_test_terminal(40, 10)

  paragraph = %Paragraph{text: "Hello!"}
  :ok = ExRatatui.draw(terminal, [{paragraph, %Rect{x: 0, y: 0, width: 40, height: 10}}])

  content = ExRatatui.get_buffer_content(terminal)
  assert content =~ "Hello!"
end

Contributing

Contributions are welcome! See CONTRIBUTING.md for development setup and PR guidelines.

License

MIT — see LICENSE for details.