Free Music Theory Reference

Music Theory

Chords, scales, modes, intervals, and the circle of fifths — explained clearly, with interactive tools

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Chord Library
300+ guitar chords with visual diagrams, finger positions, notes, and intervals
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Circle of Fifths
Interactive circle of fifths showing key signatures, relative keys, and chord relationships
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Chord Construction
How chords are built from intervals — major, minor, 7ths, extensions, and alterations
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Intervals
Every interval from unison to octave — hear them, see them on the fretboard, understand them
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Pentatonic Scales
All five pentatonic scale patterns in every key with fretboard diagrams
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Modes
The seven modes of the major scale — Ionian through Locrian — with sound and feel descriptions
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Shell Chords
Essential jazz voicings stripped to root, third, and seventh for clean comping
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Guitar Tuner
Free browser-based tuner with microphone pitch detection — on our sister site

Why Music Theory Matters

Music theory is not about memorizing rules — it is about understanding the language that connects every song, solo, and chord progression you have ever loved. When you understand theory, you stop guessing and start making intentional musical choices.

For songwriters: Theory gives you a vocabulary for the sounds in your head. Instead of stumbling onto a good chord progression by accident, you can construct one deliberately. You learn why certain chords sound tense and others sound resolved, why a minor key feels different from a major key, and how to create the specific emotional arc you are after.

For improvisers: Knowing your scales, modes, and intervals means you always know which notes will work over any chord. You stop playing "safe" pentatonic boxes and start navigating the entire fretboard with confidence. Theory does not make your playing mechanical — it gives you more tools to express what you hear inside.

For anyone learning guitar: Understanding how chords are constructed means you never have to memorize shapes without context again. When you know that a minor 7th chord is built from the root, flat third, fifth, and flat seventh, you can find that chord anywhere on the neck in any voicing. That is the difference between memorizing and understanding.

Where to Start

If you are new to music theory, start with intervals — they are the building blocks of everything else. Once you understand intervals, move to chord construction to see how intervals combine into chords. Then explore the pentatonic scales for your first scale patterns, and the modes when you are ready to expand your melodic vocabulary.

The circle of fifths ties it all together — it is the master map of music theory showing how all keys, scales, and chords relate to each other. And the chord library is your reference for any chord shape you need.

About This Site

JustMusicTheory.com is a free reference for musicians who want to understand music at a deeper level. Every tool is interactive, every explanation is written in plain language, and everything is free with no signup required.

This site is the theory companion to JustAGuitarTuner.com, our free browser-based guitar tuner. Together they cover the practical tools (tuner, metronome) and the knowledge foundation (theory, chords, scales) that every guitarist needs.

Part of the PinworthyTools network of free utility websites.