Why does a diminished seventh chord have a double flat?

Because every interval in it is a minor third, and the seventh has to be a kind of seventh above the root. Stacking three minor thirds from B♭ gives D♭, F♭ and then A double flat — which sounds like G, but calling it G would use the wrong letter and break the chord's spelling.

What is the difference between Cmaj7 and C7?

The seventh. Cmaj7 has B, a major seventh above C, and sounds settled. C7 has B♭, a minor seventh, and pulls strongly towards F. They are not interchangeable.

Can I use this for guitar?

Yes, but it gives you the notes rather than a shape. That is arguably more useful once you are past the first few chords — knowing that F♯7 is F♯ A♯ C♯ E lets you find it anywhere on the neck rather than in one memorised position.

Why do some chords look strange?

Because the draw has no key context. B♭dim7 spelled correctly contains a double flat and looks alarming; in the key it belongs to it is completely ordinary.

Random Chord Generator

Draws a chord and spells it out — the root, the quality, the notes it contains and the intervals that make it that quality. Useful for practising chord shapes, for drilling chord spelling in theory revision, and for finding somewhere unexpected to start writing.

Chord qualities

Triads

Diminished and augmented

Sevenths

Half-diminished and diminished sevenths

Draw from all root spellings

Show the interval of each note

Seed (optional)

A word or phrase makes the draw reproducible: the same word with the same settings gives the same result, so use a new word for each question.

Your chord will appear here.

What this generator does

Builds a chord from a random root and quality, and shows the notes it is made of. Chords are stacked in thirds from the root by letter name — C, then the third letter up, then the third above that — and the accidentals are then chosen to produce the interval each quality requires. Spelling a chord this way is what makes C-E♭-G a C minor triad rather than a 'C-D♯-G' that no notation program will accept.

How to use this tool

Choose which chord qualities are in the draw — major and minor triads, diminished and augmented, sevenths, and the half-diminished and diminished sevenths.
Choose whether to draw from the practical roots or from all root spellings.
Press Draw chord.
Name the notes before you look, then play it.

Understanding the controls

Chord qualities: Which types are in the draw. Triads are three notes; sevenths add a fourth and are the backbone of jazz and blues; diminished and augmented are symmetrical and unstable; the last group adds the half-diminished, diminished and minor-major sevenths.
Root range: Practical roots are the twelve chromatic notes in their common spellings. Extending to all spellings adds C♯, D♯, G♭, G♯ and A♯ — the other names for the black notes, which exist in real music but are rare enough as roots to be a theory exercise rather than a practice one.
Show intervals: Adds the interval of each note above the root — major third, perfect fifth, minor seventh. That is what actually defines the quality, and reading it alongside the notes is how the spelling stops being arbitrary.
Seed: A word or phrase makes the draw reproducible, so two students given the same word get the same chord.

Worked examples

Triads and sevenths, seed round9: Cm7: C E♭ G B♭ — root, Minor 3rd, Perfect 5th, Minor 7th.
Triads only, seed round9: Cm: C E♭ G — root, Minor 3rd, Perfect 5th.
Sevenths only, seed round9: C7: C E G B♭ — root, Major 3rd, Perfect 5th, Minor 7th. A dominant seventh.
Half-diminished and diminished sevenths only, seed round9: Cm(maj7): C E♭ G B — root, Minor 3rd, Perfect 5th, Major 7th. A minor triad with a major seventh on top.

Common use cases

Practising chord shapes without always reaching for the same four
Drilling chord spelling for a theory exam
A guitarist working through voicings up the neck
Ear training — play the chord, then identify what makes it that quality
Finding an unfamiliar starting point when writing

How this generator works

A chord is stacked in thirds: from the root's letter, two letter names are stepped for each chord tone, so a C chord uses C, E, G, B regardless of quality. It then assigns each note the accidental that produces the required interval above the root — a major third is four semitones, a minor third three, a diminished fifth six. Deciding the letter first and the accidental second is what keeps the spelling legal, and it is why a diminished seventh chord contains a double-flatted seventh rather than a note that merely sounds like a sixth.

Randomness and fairness

The root and the quality are drawn independently using the browser's cryptographic random number generator, so any allowed combination is equally likely and repeats are possible. The notes are then calculated, not drawn — the spelling is a consequence of the root and quality and involves no randomness. A seed makes the draw reproducible. That seeded mode is deterministic, not cryptographic — two students given the same word with the same boxes ticked get the same chord, and so would anybody else who guessed the word.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

It gives notes rather than voicings, so it will not tell you where to put your fingers or which inversion to use.
There is no audio and no chord diagram — the output is names and intervals.
Suspended chords and extensions beyond the seventh are not included; the useful ninths and thirteenths depend heavily on context and voicing rather than on a spelling rule.
Chord symbol conventions vary between jazz, classical and pop notation. The tool uses one consistent set and names it.
A random chord has no key context, so some draws will be theoretically valid and musically odd. That is the nature of drawing at random rather than a fault.

Common mistakes

Spelling a minor third as an augmented second: C to D♯ and C to E♭ sound the same and are different intervals. In a minor triad the third must be a kind of E, so it is E♭.
Treating a suspended chord as major or minor: It is neither — the third has been replaced, so the thing that decides major or minor is not there. That is why it wants to resolve.
Assuming any seventh chord is a dominant seventh: Cmaj7 has a major seventh, C7 has a minor seventh, and they do completely different jobs. The symbol matters.

Practical tips

Say the notes before you play the chord; if you can only find it by shape, you do not yet know it.
Draw ten chords and play them all in one position before moving on, so you are practising the voicing as well as the chord.
Pair this with the scale generator: play a scale, then draw chords and work out which ones belong to that key.

Privacy and your data

Nothing is entered and nothing is stored. Chords are calculated in your browser; none of them is uploaded or written into the page address, and analytics records only that the tool was used — never which chord was drawn or which qualities were enabled.

Frequently asked questions

Why does a diminished seventh chord have a double flat?: Because every interval in it is a minor third, and the seventh has to be a kind of seventh above the root. Stacking three minor thirds from B♭ gives D♭, F♭ and then A double flat — which sounds like G, but calling it G would use the wrong letter and break the chord's spelling.
What is the difference between Cmaj7 and C7?: The seventh. Cmaj7 has B, a major seventh above C, and sounds settled. C7 has B♭, a minor seventh, and pulls strongly towards F. They are not interchangeable.
Can I use this for guitar?: Yes, but it gives you the notes rather than a shape. That is arguably more useful once you are past the first few chords — knowing that F♯7 is F♯ A♯ C♯ E lets you find it anywhere on the neck rather than in one memorised position.
Why do some chords look strange?: Because the draw has no key context. B♭dim7 spelled correctly contains a double flat and looks alarming; in the key it belongs to it is completely ordinary.