Music Theory Decoder is the complete music theory toolkit — an interactive Circle of Fifths, 20 scales, 30 chord types, 12 classic progressions with playback, and 7 pro tools. Built for real musicians, not cartoon lessons — see who it's for.
Replace your tuner app, metronome app, theory book, chord library, and vocal tools with one unified experience.
Tap any key on the interactive Circle of Fifths to see its diatonic chords — I, IV, V, ii, iii, vi, vii° — clearly laid out. Flip the card for 12 classic progressions (Pop Classic, ii–V–I, 12-Bar Blues, Pachelbel, Andalusian Cadence and more) auto-transposed to your key, with playback at 60–120 BPM.
Twenty scales across five categories: Modes (Ionian through Locrian), Minor (natural, harmonic, melodic, pentatonic), World (blues, flamenco), Japan (Hirajoshi, Insen, Yo), and Middle East (Phrygian Dominant, Double Harmonic, Hijaz). Every scale renders on guitar fretboard and piano keyboard, with audio preview up and down.
Thirty chord types across all twelve roots — triads, 7ths, 6ths, altered dominants, extended 9 / 11 / 13 voicings. Multiple guitar fingerings per chord. Every interval is labeled, so you understand what you are playing.
Sixteen in-depth sections: Intervals, Scales, Three Minor Scales, Circle of Fifths, Chord Construction, Diatonic Chords, Chord Functions, Progressions, Cadences, Voice Leading, Secondary Dominants, Borrowed Chords, Modal Chords, Extended & Altered Chords, Guitar Theory, Piano Theory — with interactive staff notation.
A full shelf of pro utilities: chromatic tuner, metronome with compound time and swing, reference drone, real-time vocal pitch monitor, vocal warm-up coach, capo calculator, and a key transposer. Detailed below.
No accounts, no analytics, no ads, no third-party SDKs. Microphone audio for the tuner and vocal features is processed on your device and never recorded or transmitted. Everything works offline.
Every tool is tuned for working musicians and built with the same dark, bold design as the rest of the app.
Fully chromatic tuner with smooth spring animations. Works for guitar, bass, piano, brass, strings — any pitched instrument.
6/8, 9/8, 12/8 time signatures, swing slider, beat accents, tap tempo, and four click sounds. Built for real practice.
Four waveforms, three octaves. Ideal for ear training, vocal practice, and modal improvisation.
Real-time pitch monitor — see every note you sing with cent-accurate tuning feedback. A rare tool in theory apps.
Breathing coach plus scale exercises with real-time pitch tracking — a complete vocal warm-up flow.
Pick a key you want and a key you can play — the capo calculator shows the fret instantly.
Move any chord progression to any key with a single tap. Perfect for lead sheets and singer-songwriter work.
Every theory section connects back to the interactive Circle of Fifths, scales, and chords. Read a definition, hear it, see it on the fretboard or keyboard, and you have understood it — not memorized it.
Written for first-time learners and working musicians alike. No condescending tone, no gamification, no gated content — made by a musician, not a content farm.
One unified experience instead of six separate apps with six different UIs, five of them begging for subscriptions.
Free Sing, Vocal Warm-Up, and Drone form a complete practice suite for singers — a category most theory apps ignore entirely.
Dark theme, bold typography, Bebas Neue and DM Sans. A working tool you will not be embarrassed to open in the rehearsal room.
Every theory section links to the interactive Circle of Fifths, scales, and chords. Hear it, see it, understand it — then play it.
Works on the tube, on a plane, in a rehearsal room with no Wi-Fi. No data leaves your phone because nothing is collected in the first place.
Made by CODE lunatics, an independent developer who needed the app to exist and could not find it. Every design decision comes from actual playing.
The Circle of Fifths arranges the twelve musical keys so that neighbouring keys share most of their notes. Once you can read it, you can see at a glance which chords belong in a key, which keys are closely related, and how to transpose a progression.
Music Theory Decoder is built around an interactive version of this circle — every chord, scale, and progression in the app traces back to it.
No. The app works fully offline. All audio, pitch detection, and theory content is processed on your device. The app makes no network requests to our servers — we do not operate any.
No. No accounts, no analytics, no telemetry, no advertising SDKs. Microphone audio used by the tuner and vocal tools is analyzed in real time on your device and never recorded or transmitted.
The full policy is at our privacy page.
The app is instrument-agnostic for theory, scales, and progressions. Guitar fretboards and piano keyboards render for every scale and chord, with multiple guitar fingerings per chord. The chromatic tuner works for any instrument that produces a pitched tone.
Yes. Every theory section is written to be read by someone new to music theory, and each section links to the interactive Circle of Fifths, scales, and chords so you can hear what you are reading about.
Advanced topics like secondary dominants and voice leading are also covered for more experienced musicians.
Yes. iOS is released first, with Android following shortly after.
Pricing is finalized close to launch. The app is designed to ship with all features included — no subscriptions, no locked chord libraries behind in-app purchases. Follow @codelunatics on Instagram for launch details.
The tuner is fully chromatic and cent-accurate, and ships alongside a serious metronome (compound time, swing, tap tempo, four click sounds), a reference drone (four waveforms, three octaves), and two vocal pitch monitors. You replace several apps with one.
Music Theory Decoder started as a working musician's frustration: flipping between a tuner app, a metronome app, a theory book, a chord library, and a vocal pitch tool — none of them designed to talk to each other.
CODE lunatics is an independent studio. Feedback, bug reports, and feature requests are welcome there or by email.
iOS first, Android shortly after. Follow @codelunatics on Instagram for the launch date and a first look at the final UI.
