Theory, graded on your instrument
Thirty lessons across intervals, chords, scales, progressions and ear, each one completed by playing it on a MIDI keyboard or a guitar through an interface.
For guitar, keys and bass · macOS · Windows · Browser
Learn the theory.
Learn the theory.
Practise the songs.
Play the gig.
Harmony Lab is a workbench for working musicians: a theory curriculum you complete on your instrument, a practice room that hears what you play and shows the harmony as it moves, a library that grows into a repertoire, and a music stand that walks a setlist song by song. Mac, Windows and the browser, with the listening done on your own machine.
Free, forever, for the listening, every instrument view and the first tier of lessons. No account needed. Early access is by invitation while v1 is finished: say what you play and a build follows.
Lessons
30
Intervals, chords, scales, progressions and ear, in four rising tiers. Every one graded by what you play.
Songs in the box
349
Public-domain standards with melody, chords and lyrics, before you import a thing.
Audio uploaded
0 bytes
Key and chord analysis runs on your own machine. No recording or live input ever leaves it.
Harmony Lab
PlaySongExploreLearnLibrary
0:00
Guitar
File Misty
Playing
Key
Eb
major
Locked · chosen, not heard
Chord
Ebmaj7
E♭ G B♭ D
bar 1 of 8
Tempo
4/4 · 1 bar in
68
bpm
Tap
Click ◯
▷ Count me in
Ready no loop
Loop editor →
Controls
Misty
by
Erroll Garner
Eb major · 68
ChordsSheetHorizonMelody
Guitar · E♭ major ⇆ E♭ minor · equator 11
Diagonal over the boxes
Major / minor
major — the track, over its box
minor — the track, over its box
ANALYSIS 22 050 HzFFT 2048HOP 512 · 23.2 msRING OK
The Play screen: Misty, the chart following the beat, the key pinned, the chord tones ringed on the neck as each change arrives.
01 — WhyTheory and practice, finally in the same room.
The theory lives in a book.
The music lives in your hands.
You can know what a ii–V–I is and still not hear one go by. You can play a song a hundred times and never learn why the bridge lifts. The two halves of musicianship are usually taught in different rooms by different tools, and the gap between them is where most players stall for years.
Harmony Lab puts the chart, the instrument and the explanation on one screen. Every lesson is played, not clicked. Every song you practise shows its harmony as it moves. Every chord you wonder about will tell you what it is doing, and what else could go there.
Understand what you play. Play what you understand.
02 — The workbenchFour rooms, one song at the centre.
One song, four rooms.
Whatever you are working on is the same song in every room: the lesson you are drilling, the chart you are practising, the harmony you are taking apart, and the setlist you are taking out on Friday.
01 · Learn
02 · Practise
The harmony in view while you play
Charts with a backing band and a click, bar-range drills that ramp the tempo, a recording slowed down or shifted into your key, and the chord tones lit on the neck as each change arrives.
03 · Explore
Why a chord works, and what else would
The circle of fifths, a function map, a palette of alternatives for any chord, and named routes from one key to another, each with its reason.
04 · Stage
From library to setlist to music stand
A repertoire with tags and practice history, setlists with a key, tempo and capo per song, printed stage sheets and booklets, and a Perform mode you drive from a pedal.
03 — LearnThirty lessons on a rising helix.
Theory you complete
on your instrument.
Five strands run side by side: intervals, chords, scales, progressions and ear. Each comes back at four rising levels rather than being finished once and forgotten, so you meet the major scale in your first hour and again, differently, near the top. Triads come before seventh chords, because the second is unplayable without the first.
Every lesson is graded by what you play, on a MIDI keyboard or a guitar through an interface, and you step through it from a pedal or the edge keys so your hands never leave the instrument. Flashcards and ear drills come back on a spaced-repetition schedule. A short placement test drops you in at the right rung on each strand, and a lesson you abandon halfway earns nothing: no points, no streak. On purpose.
Interval size & the pillars
Intervals · Tier 1
IntervalsChords
ScalesProgressions
Ear
01FoundationsFree9 lessons
Interval size, your first triads, the major and natural-minor scales, and the chords they generate. The first rung of all five strands.
02Color & FunctionPro9 lessons
Quality and motion. The dominant 7th and the restless tritone, altered triads, the minor-scale colours, cadences, and what each chord is doing in the key.
03Putting It TogetherPro7 lessons
Real harmony in play. The seventh-chord family and its inversions, pentatonics and blues, ii–V–I, and the pop axis.
04AdvancedPro5 lessons
The far reaches. Extensions and alterations, the modes, secondary dominants, and hearing function without looking.
04 — PractiseDrawn where your hands already are.
Practise with the harmony
in front of you.
Open a chart, or let it listen to a recording, and the instrument shows the key's scale as the ground, the chord tones of the moment on top, and the tones the next chord brings in already outlined, so a change is something you lean into rather than something that happens to you. The board is a map of the key with an equator through it: major under your pinky below the line, the same shape turning minor under your index finger above it.
Drag across four bars to drill them, and let the tempo climb a few beats a minute each pass, or cycle the key every few rounds. Slow a recording to half speed without changing its pitch, or shift it into your key. Play something good and press Loop that: the phrase you just played is captured after the fact and lands on the chart. A click, a count-in and a backing band keep you honest.
Guitar · board
E♭ major ⇆ E♭ minor · equator 11
Chord tones — every note of the sounding chord, wherever it falls under your hand.
RingedThe root of the key
SplitBoth hands share this note
NumberedScale degree, not note name
The equatorWhere major becomes minor
05 — ExploreThe theory behind the chart, one click away.
Why this chord works,
and what else would.
Every chord on a chart can explain itself. Hover one and its fingering appears. Open its menu and a palette of alternatives is grouped by why each one works: an extension, a diatonic substitute, an inversion, a secondary dominant, a chord borrowed from the parallel mode, a tritone sub. The idiomatic answers come first.
Ask how to get from C to E♭ and Explore lists the routes a teacher would name, each as a chord sequence with the one line that says why it works. Tap one and it joins the path on the circle of fifths, so you hear the move on the same screen you reasoned about it. Roman numerals or Nashville numbers, your choice, everywhere a chord is named.
Explore · Modulation
How do I get from C major to E♭ major?
ranked · tap a route to hear it
01
Modal-interchange pivot · Fm
CIFmiv → iiB♭7V7E♭I
Fm is iv in C minor — the parallel mode you can borrow from at any time — and ii in E♭ major. Borrowing it moves you before the ear notices, and B♭7 → E♭ closes the door behind you.
02
Applied dominant · B♭7
CIB♭7V7E♭I
B♭7 is the V7 of E♭ major: its tritone only resolves one way, so the new tonic arrives with authority from anywhere. Put Fm7 in front of it for a full ii–V if you want two bars of warning.
03
Chromatic mediant · A♭
CIA♭♭VI → IVE♭I
A♭ sits a third from C and shares exactly one tone with it — close enough to hinge on, far enough to sound like somewhere new.
04
Tritone substitution · E7
CIE7III7 → ♭II7E♭I
E7 shares its tritone with B♭7, the V7 of E♭ major, so it pulls the same way — but the root slides down a semitone into E♭ instead of up a fourth.
the pivot — heard in both keys
Every route is a chord sequence plus the reason it works. The same palette opens on any chord in a chart.
06 — RepertoireA library that knows what you have worked on.
Songs you are learning.
Songs you know.
Songs for Friday.
The library keeps every chart you save, with tags, favourites, when you last played it, and how many minutes you have put into each section, so a setlist can tell you which songs are ready and which are not. It starts full: 349 public-domain standards with melody, chords and lyrics come in the box.
Bring in what you haveImport iReal Pro and MusicXML files, plain chord sheets by the folder or the zip, or a photo of a page. Transpose in one tap, with horn keys and capo built in.
Write it downChords over lyrics, or a staff lead sheet in a Real Book hand or a classic engraving. Sections, repeats and endings, alternate chords, and undo all the way back.
Get it back outPrint any chart, a staff lead sheet, or a booklet of any songs with a table of contents. Export MusicXML, Guitar Pro tab, iReal, MIDI and WAV.
Ask about itThe co-writer answers questions about the open chart: why a chord works, what to try in the bridge, how to voice it on guitar. Your own Claude can read and shape the song directly, over the built-in MCP server.
The Library: five saved charts, tagged and starred, each with when it was last played and how long it has been practised.
07 — StageA music stand that turns its own pages.
The next chord arrives
before you need it.
Build a setlist from the library with a key, a tempo, a capo, a count-in and stage notes for each song, and print the one-page stage sheet. Then open Perform: a fullscreen music stand that walks the list song by song in big type, the next song already named, the chart scrolling to keep what is coming in view. Previous, next, count-in and play sit on a pedal or the arrow keys, and a song can segue straight into the next without anyone touching the laptop.
For playing live over music, Horizon flows toward a fixed NOW line, so the sounding chord is always in the same place on screen and the one coming is already in view, with its fingering drawn above the lane. Blocks are coloured by what a chord is doing in the key: home, away, pulling home.
Perform mode: song 1 of 5 in Friday's set, the count-in and the stage note in the header, the next song already named, the whole thing driven from a pedal.
Horizon
E♭ major · bar 1 of 8 · 46 px / beat
sounding now
home · tonic
away · pre-dominant
pulling home · dominant
borrowed · no claim made
08 — ListeningOn your device. Not a setting, an architecture.
It hears the music.
The audio stays in the room.
Point it at a file, a YouTube link, your mic or interface, or whatever your computer is playing, and it finds the key, the tempo, the chords and the sections as the music goes by. Resampling, the transform, chord and key inference: all of it runs on your own machine, inside the app you launched. No recording or live input is ever uploaded, and nothing is matched against a catalogue.
No account to playInstall it and play. Signing in is optional, and only links the history you already have so it follows you between machines.
Your own AIThe app never calls a language model to do the listening. The built-in MCP server lets your Claude read and shape the open song. Your model, your context, your machine.
What does leave, namedTwo things. A question to the co-writer sends that question and the chart it is about. Usage data, which chords and keys you worked on and never audio or your questions, is on by default and switches off in Settings in one click, permanently.
09 — PricingFree where it should be.
The listening is free.
Forever.
Hearing the key and the chords, every instrument view, the Explore map and the first tier of lessons cost nothing, on unlimited songs, with no account. Pro pays for the depth: the practice transforms, the rest of the curriculum, setlists and Perform, import and export, and sync across your machines.
Free
Free
forever · no account
Everything that listens, everything that draws.
- Live key, chord, beat and section detection, on unlimited songs
- Every source: mic, interface, system audio, file and YouTube
- Guitar, bass, keyboard, ukulele and notation views, the tuner, Roman and Nashville lenses
- Charts with sections, transpose and capo, click and count-in, section loop, backing band, lyrics
- Explore: the circle of fifths, the function map and the tree
- Unlimited local library, and the MCP server driven by your own Claude
- Learn tier 1: 9 of the 30 lessons, and the ear drills
- MIDI and single-chart PDF export · 15 co-writer turns a month
Pro
$9
a month · $79 a year · $199 once
One licence, every surface: web, Mac and Windows. Never per platform.
- Slow a recording down without changing its pitch, or shift its key
- Drill any bar range, with the tempo ramp and key cycling
- Setlists, Perform mode, stage sheets, booklets and printing
- Learn tiers 2 to 4: the other 21 lessons, streaks, history and the spiral
- The looper and Loop that, and the co-writer on every screen: 75 turns a month, or your own key
- The reharmonisation palette and the modulation routes
- Import: iReal Pro, MusicXML, bulk folders, a photo of a chart
- Export and interop: MusicXML, Guitar Pro, iReal, WAV, Ableton Link and live MIDI out
- Cloud sync across your machines
Pro opens with v1, with a 14-day trial and no card. It unlocks features, never your own work: stop paying and the app drops back to Free rather than locking, and every song you made stays openable and exportable forever.
Ready when you are
Bring a song you are still learning.
Play it, drill the bars that trip you, ask why the bridge works, and put it on Friday's setlist. Early access is by invitation while v1 is finished: request one, say what you play, and a build follows.
MACOS 12+ · WINDOWS 10+ · CHROME, EDGE, SAFARI