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pedrozath/coltrane

🎹🎸A music theory library with a command-line interface
Source code at GitHub https://github.com/pedrozath/coltrane
pedrozath/coltrane.json
{
  "createdAt": "2017-05-30T18:29:34Z",
  "defaultBranch": "master",
  "description": "🎹🎸A music theory library with a command-line interface",
  "fullName": "pedrozath/coltrane",
  "homepage": "",
  "language": "Ruby",
  "name": "coltrane",
  "pushedAt": "2025-01-29T18:17:15Z",
  "stargazersCount": 2393,
  "topics": [
    "gem",
    "music",
    "ruby"
  ],
  "updatedAt": "2025-11-24T21:12:45Z",
  "url": "https://github.com/pedrozath/coltrane"
}

Build Status Gem Version Maintainability Test Coverage

Coltrane

Section titled “Coltrane”

A music calculation library/CLI written in Ruby.

![Coltrane]!(img/coltrane-logo.png)

CLI (Command Line Interface)

Section titled “CLI (Command Line Interface)”

![Screenshot]!(img/using-coltrane.gif) ![Screenshot]!(img/guitar-chords.png)

Features

Section titled “Features”
  • Generate chord progressions for Jazz, Blues, Pop, or custom and see how to play them
  • Seek chords, see their notes and how to play them
  • Seek scales, see their notes and see how to play them
  • Find chords that are common between 2 scales
  • Find scales containing a chord or a set of notes
  • Find possible progressions of a chord sequence
  • All of the above can be seen on guitar, bass, piano or ukelele representations, no sheet music needed

How to discover a chord name using the notes

Section titled “How to discover a chord name using the notes”
Terminal window
coltrane find chord by notes notes:C-E-G


CM:  C E G

To see it on guitar:

Terminal window
coltrane show chord chord:CM7 chord_representation:Guitar


CM:


   ⬤    ⬤  ⬤   ⬤    ⬤  ⬤   ⬤    ⬤             ⬤  ⬤
   ┍━┯━┯━┯━┯━┑    ┍━┯━┯━┯━┯━┑    ┍━┯━┯━┯━┯━┑    ┍━┯━┯━┯━┯━┑
3  │ ⬤│ │ │ │ 8  │ │ │ │ ⬤│ 3  │ ⬤│ │ │ ⬤1  │ │ │ │ ⬤│
   ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥
4  │ │ │ │ │ │ 9  │ │ │ │ │ │ 4  │ │ │ │ │ │ 2  │ │ ⬤│ │ │
   ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥
5  │ │ ⬤│ ⬤│ 10 │ ⬤⬤│ │ │ 5  │ │ ⬤│ ⬤│ 3  ⬤⬤│ │ │ │
   ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥    ┝━┿━┿━┿━┿━┥
6  │ │ │ │ │ │ 11 │ │ │ │ │ │ 6  │ │ │ │ │ │ 4  │ │ │ │ │ │
   ┕━┷━┷━┷━┷━┙    ┕━┷━┷━┷━┷━┙    ┕━┷━┷━┷━┷━┙    ┕━┷━┷━┷━┷━┙

PS: It looks way better on the terminal 😒, specially on iTerm

How to discover a Scale by providing chords

Section titled “How to discover a Scale by providing chords”

You shall provide chords separated by dashes (--chords CM7-Dm7-EM) or notes (--notes C-Ab-F-G).

For example:

Terminal window
coltrane find scale by chords chords:E6/9-BM


Pentatonic Major C(1) C#(3) D(3) D#(1) E(5) F(0) F#(4) G(2) G#(2) A(4) A#(0) B(5)
Blues Major      C(2) C#(4) D(3) D#(2) E(5) F(1) F#(4) G(2) G#(3) A(4) A#(1) B(5)
Harmonic Minor   C(3) C#(5) D(2) D#(4) E(4) F(3) F#(4) G(2) G#(5) A(3) A#(3) B(4)
Hungarian Minor  C(2) C#(6) D(2) D#(4) E(3) F(3) F#(5) G(1) G#(5) A(3) A#(4) B(4)
Pentatonic Minor C(1) C#(5) D(0) D#(4) E(2) F(2) F#(4) G(0) G#(5) A(1) A#(3) B(3)
Blues Minor      C(2) C#(5) D(1) D#(4) E(2) F(3) F#(4) G(1) G#(5) A(2) A#(4) B(3)
Whole Tone       C(3) C#(3) D(3) D#(3) E(3) F(3) F#(3) G(3) G#(3) A(3) A#(3) B(3)
Flamenco         C(3) C#(4) D(2) D#(5) E(3) F(3) F#(4) G(3) G#(5) A(2) A#(4) B(4)
Major            C(2) C#(4) D(4) D#(2) E(6) F(1) F#(5) G(3) G#(3) A(5) A#(1) B(6)
Natural Minor    C(2) C#(6) D(1) D#(5) E(3) F(3) F#(5) G(1) G#(6) A(2) A#(4) B(4)

When on terminal, the command above will highlight the Scales that have all needed notes. The number in the parenthesis show how many chord notes were included.

How to find common chords

Section titled “How to find common chords”

You may use this command to find a chord that may serve as bridge to a different scale/key (i.e. modulation). Coltrane offers you a command to find common chords shared between both keys/scales. Here is how you use it. Say you wanna transition from C Major to D Natural Minor.

Terminal window
coltrane find common chords in scales


Dm:  D F A
Am:  A C E
Dm7: D F A C
Am7: A C E G
CM:  C E G
FM:  F A C
CM6: C E G A
FM6: F A C D
C6/9: C E G A D
F6/9: F A C D G
C6/9(add11): C E G A D F
[...]

You can also see the output in a graphical representation:

Terminal window
Dm:


┌─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─╥─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─┐
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ ║ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ │
│  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  │
│  ║D♮║  ║F♮║  ║A♮║  ║  ║D♮║  ║F♮║  ║A♮║  │
└──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──┘


Am:


┌─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─╥─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─┐
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ ║ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ │
│  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  │
│C♮║  ║E♮║  ║  ║A♮║  ║C♮║  ║E♮║  ║  ║A♮║  │
└──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──┘


[...]

Quickly generate chord progressions

Section titled “Quickly generate chord progressions”
Terminal window
coltrane show progression progression:Jazz representation:Piano root:A


Bm7:


┌─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─╥─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─┐
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ │ ││ │ ║ │F││ ││ │ ║ │ ││ │ ║ │F││ ││ │ │
│ │ ││ │ ║ │♯││ ││ │ ║ │ ││ │ ║ │♯││ ││ │ │
│ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ ║ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ │
│  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  │
│  ║D ║  ║  ║  ║A ║B ║  ║D ║  ║  ║  ║A ║B │
└──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──┘


E7:


┌─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─╥─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─┐
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ │ ││ │ ║ │ ││G││ │ ║ │ ││ │ ║ │ ││G││ │ │
│ │ ││ │ ║ │ ││♯││ │ ║ │ ││ │ ║ │ ││♯││ │ │
│ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ ║ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ │
│  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  │
│  ║D ║E ║  ║  ║  ║B ║  ║D ║E ║  ║  ║  ║B │
└──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──┘


A7:


┌─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─╥─┬─┬┬─┬─╥─┬─┬┬─┬┬─┬─┐
│ │ ││ │ ║ │ ││ ││ │ ║ │ ││ │ ║ │ ││ ││ │ │
│ │C││ │ ║ │ ││ ││ │ ║ │C││ │ ║ │ ││ ││ │ │
│ │♯││ │ ║ │ ││ ││ │ ║ │♯││ │ ║ │ ││ ││ │ │
│ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ ║ ┕╥┙┕╥┙ ║ ┕╥┙┕╥┙┕╥┙ │
│  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  ║  │
│  ║  ║E ║  ║G ║A ║  ║  ║  ║E ║  ║G ║A ║  │
└──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──╨──┘

You can say Jazz, Pop, Blues, etc. You can also generate progressions in a custom way, using roman numerals:

Terminal window
coltrane custom progression progression_notation:I-vi-V-iidim representation:Text key:D

Generate fretboard sheets for improvising

Section titled “Generate fretboard sheets for improvising”

Sometimes you wanna see the scale on guitar for improvising:

Terminal window
coltrane show scale scale:Pentatonic-Major tone:F


F Pentatonic Major:


E -- | F  -- G  -- A  -- -- C  -- D  -- -- F  -- G  -- A  -- -- C  -- D  --
A A  | -- -- C  -- D  -- -- F  -- G  -- A  -- -- C  -- D  -- -- F  -- G  --
D D  | -- -- F  -- G  -- A  -- -- C  -- D  -- -- F  -- G  -- A  -- -- C  --
G G  | -- A  -- -- C  -- D  -- -- F  -- G  -- A  -- -- C  -- D  -- -- F  --
B -- | C  -- D  -- -- F  -- G  -- A  -- -- C  -- D  -- -- F  -- G  -- A  --
E -- | F  -- G  -- A  -- -- C  -- D  -- -- F  -- G  -- A  -- -- C  -- D  --


             03    05    07    09       12       15    17    19

ProTip: You can force the guitar frets visualization for chords too using the --on guitar_frets option.

Finding the progression of a chord sequence

Section titled “Finding the progression of a chord sequence”

Perhaps this is the most complex operation that Coltrane performs. It searches the chords on all known scales, generates the progression notation and print in, sorted by notes left out. That is because most songs, specially knowadays, may use chords that contain notes which are outside of that scale.

This command us to analyze songs and discover what they have in common, even tho they have different notes.

Let’s say we want to find the possible progressions of Red Hot Chili Pepper’s Otherside:

Terminal window
coltrane find progressions from chords chords:Am-F-C-G


i-VI-III-VII   in A Natural Minor (0 notes out)
vi-IV-I-V      in C Major (0 notes out)
iii-I-V-II     in F Major (1 notes out)
vi-III-VII-IV  in D Hungarian Minor (1 notes out)
v-III-VII-IV   in D Natural Minor (1 notes out)
ii-VII-IV-I    in G Hungarian Minor (2 notes out)
ii-VII-IV-I    in G Natural Minor (2 notes out)
vii-V-II-VI    in A# Major (2 notes out)
iv-II-V-III    in D Pentatonic Minor (2 notes out)
v-II-VI-III    in D Blues Minor (2 notes out)
iii-I-IV-II    in F Pentatonic Major (2 notes out)
iv-I-V-II      in F Blues Major (2 notes out)

PS: Notice that vi-IV-I-V is the well known I-V-vi-IV progression, used in a lot of songs.

Interactive mode (shell)

Section titled “Interactive mode (shell)”

Simply type coltrane or coltrane shell to enable interactive mode. You can then run commands without typing coltrane before, E.G.: scale D harmonic minor

Installation

Section titled “Installation”

Installation is done through the RubyGems package manager:

Terminal window
gem install coltrane

[!NOTE] RubyGems comes packaged with the standard Ruby installation. You can find instructions on how to install Ruby here.

Once you install the gem, the CLI is installed in your system and it’s ready to be used.

Any questions? Feature requests? Bugs?

Section titled “Any questions? Feature requests? Bugs?”
  1. Find me on Twitter. I’ll be glad to answer.
  2. Open an issue.
  3. Join our chatroom

Extra

Section titled “Extra”

Contributing

Section titled “Contributing”

How to contribute

Section titled “How to contribute”
  1. Fork this code
  2. Install the test suite (RSpec) by running good old bundle command
  3. Make your changes and maybe write a test or two.
  4. Check if specs pass bundle exec rspec spec
  5. Submit a PR.

License

Section titled “License”

The gem is available as open source under the terms of the MIT License.

by Pedro Maciel | twitter | pedro@pedromaciel.com