Key Signature Finder

The tool uses the Krumhansl-Schmuckler key-finding algorithm, a scientifically validated method from music cognition research. It builds a histogram of how often each of the 12 pitch classes (C, C#, D, ..., B) appears in the music, then computes a correlation coefficient against 24 key profiles (12 major + 12 minor). The key profile with the highest correlation is the detected key. The profiles are based on empirical data from probe-tone studies by Krumhansl and Kessler (1982). For chord-based input, each chord is weighted by its diatonic function within a potential tonal center, making this method robust even for short chord sequences.

Accuracy depends on the input. With 30+ seconds of clear audio containing a variety of notes, accuracy is typically 85-95%. Short clips or songs that modulate between keys may produce lower confidence. Chord input is often the most reliable method since chord progressions strongly imply a key. Songs in minor keys may sometimes show the relative major as a close second.

Relative keys share the same key signature (same sharps/flats) but have different tonics — for example, C Major and A Minor are relative keys (both have zero sharps/flats). Parallel keys share the same tonic but differ in mode — for example, C Major and C Minor are parallel keys (same root note, different quality).

The capo table shows how placing a capo on different frets transposes the song to keys with more open-chord-friendly shapes. For example, if the detected key is Eb Major, capo 1 lets you play D Major shapes, and capo 3 lets you play C Major shapes. The tool highlights positions that produce the easiest open chord keys (C, G, D, A, E, Am, Em, Dm).

Yes! Switch to the Enter Chords tab and type your chord progression (e.g., "Am F C G"). The tool scores each chord against all 24 keys: +2 points for a diatonic chord, +1 for a secondary dominant, and -1 for a non-diatonic chord. This method is often the most reliable since chord progressions provide strong key information.

Yes, 100% private. All key detection runs entirely in your browser using the Web Audio API. No audio is recorded, stored, or transmitted to any server. The tool works completely offline once loaded.

This is a known limitation of pitch-class-based key finding. A minor key and its relative major share the same seven notes — for example, A minor and C major both use C, D, E, F, G, A, B. The algorithm uses note frequency to distinguish them, so the tonic chord or leading-tone resolution carries the most weight. To improve minor-key detection: let the audio run longer (the tonic note tends to land on strong beats), or use the Enter Chords tab and include the i and v chords — the tool will correctly score those as favouring the minor key.

Yes — that's one of the most practical uses. First detect the song's current key, then use the online transpose tool to shift up or down by semitones until the melody fits your comfortable singing range. The key signature finder shows you the starting point; the transposer handles the math. Guitarists can also use the capo suggestions table here directly to find the fret that puts the song in an easier key without changing tuning.

The confidence score is the Pearson correlation coefficient between the detected pitch-class histogram and the best-matching key profile, scaled to a percentage. A score above 75% generally means the key is reliable; 50–75% indicates a plausible result worth cross-checking; below 50% means the audio is too short, too noisy, or the piece genuinely modulates between keys. If confidence is low, check the "All 24 Keys Ranked" section — a close second key may be a valid modulation target. Atonal or modal music may never produce high confidence against any standard major/minor profile.

Absolutely. Knowing the key is the first step in transcription because it tells you which scale positions to expect, which accidentals are part of the key signature, and which notes are chromatic passing tones. For songwriting, once you know the detected key you can use the diatonic chords panel to see every naturally occurring chord — the I, ii, iii, IV, V, vi, and vii° — and combine them with the chord progression generator to build or extend your arrangement.