Render sparklines, line charts, candlestick charts, and bar charts directly in the terminal. Pure Ruby, zero dependencies.

All chart types render to plain strings with ANSI color codes — composable with any TUI framework (rcurses, curses, or raw terminal output).

• Sparklines — compact single-line charts using ▁▂▃▄▅▆▇█
• Line charts — high-resolution braille dot plotting (2×4 dots per cell)
• Candlestick charts — OHLC financial charts with green/red coloring
• Bar charts — horizontal and vertical with sub-cell precision
• 256-color and RGB — supports integer color codes and hex strings
• No dependencies — pure Ruby, no native extensions
• String output — no direct terminal I/O, works anywhere

gem install termchart

Or add to your Gemfile:

gem 'termchart'

Map values to 8 eighth-block characters on a single line.

require 'termchart'

puts Termchart.spark([1, 3, 5, 2, 8, 4, 6])
# => ▁▃▅▂█▄▆

puts Termchart.spark([10, 20, 30, 25, 40], color: :green)
# => ▁▃▅▄█  (in green)

Supported color names: :red, :green, :blue, :yellow, :cyan, :magenta, :white, :gray, :orange

Braille-dot line charts with Y-axis labels. Each terminal cell provides 2×4 sub-pixel resolution via Unicode braille patterns (U+2800–U+28FF).

chart = Termchart::Line.new(width: 60, height: 20)
chart.add(prices, color: 82, label: "SPY")
chart.add(gold,   color: 226, label: "GLD")
puts chart.render

Output:

 460┤⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⠔⠊⠢⡀⠀⠀⠀⠀⠀⢀⡠⠊
    │⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⠔⠁⠀⠀⠀⠈⠢⡀⠀⢀⠔⠊
    │⠀⠀⠀⠀⠀⠀⢀⡠⠤⠒⠢⡀⠀⠀⠀⣀⠔⠁⠀⠀⠀⠀⠀⠀⠀⠈⠔⠁
 440┤⠀⠀⠀⢀⡠⠊⠁⠀⠀⠀⠀⠈⠢⡠⠊⠁
    │⠀⠀⣀⠃⠀⠀⠀⠀⠀⠀⠀⠀⠀⠁
    │⠀⡰⠁
 420┤⡰⠁
     ━━ SPY

OHLC candlestick charts for financial data. Green for up candles, red for down.

chart = Termchart::Candle.new(width: 60, height: 20)
chart.add([
  { o: 100, h: 105, l: 98,  c: 103 },
  { o: 103, h: 107, l: 101, c: 99  },
  { o: 99,  h: 104, l: 97,  c: 102 },
  { o: 102, h: 108, l: 100, c: 106 },
])
puts chart.render

Uses │ for wicks and █ for bodies. Y-axis labels on the left at 5 price levels.

Horizontal and vertical bar charts with sub-cell precision using eighth-block characters.

chart = Termchart::Bar.new(width: 40, orientation: :horizontal)
chart.add("GLD", 185.50, color: 226)
chart.add("SPY", 450.00, color: 82)
chart.add("SLV", 22.30,  color: 245)
puts chart.render

GLD │███████████▏            185.50
SPY │████████████████████████    450
SLV │█▍                       22.30

chart = Termchart::Bar.new(width: 30, height: 10, orientation: :vertical)
chart.add("Q1", 80, color: 82)
chart.add("Q2", 95, color: 82)
chart.add("Q3", 70, color: 196)
chart.add("Q4", 110, color: 82)
puts chart.render

All chart types accept colors as:

For custom visualizations, use the canvas classes directly.

Character grid where each cell holds a character, foreground color, and background color.

canvas = Termchart::Canvas.new(40, 10)
canvas.set(5, 3, "█", fg: 196, bg: 233)
puts canvas.render

Each cell maps to a 2×4 braille dot grid for sub-cell resolution.

canvas = Termchart::BrailleCanvas.new(40, 10)
# Pixel space: 80×40
canvas.set_dot(15, 25, fg: 82)
puts canvas.render

Termchart is designed to compose with rcurses panes:

require 'rcurses'
require 'termchart'

pane = Rcurses::Pane.new(2, 2, 60, 20)
chart = Termchart::Line.new(width: 60, height: 20)
chart.add(data, color: 82, label: "Price")
pane.text = chart.render
pane.refresh

Unlicense — Public Domain

Geir Isene — https://isene.com