Key Signature Finder

Detect the key of any song from live audio, chord progressions, or selected notes. See the key signature with confidence score, diatonic chords, relative and parallel keys, guitar capo suggestions, and staff notation. 100% browser-based, no downloads, no data uploaded.

🔒 100% private — all key detection runs locally in your browser. No audio is ever uploaded or stored.

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Space Start/Stop F Freeze R Reset C Calibrate

🎤 Microphone:

Sensitivity: -45 dB

Click "Start Listening" to detect the key of music playing near your microphone

Pitch Class Histogram

📂 Drag & drop an audio file here, or browse

Supports MP3, WAV, OGG, FLAC, M4A

Detected Key

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Confidence

Key Signature

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Related Keys

Diatonic Chords

Detect a key to see its diatonic chords

Guitar Capo Suggestions

Capo Fret	Play As	Open Chords
Detect a key to see capo suggestions

All 24 Keys Ranked by Confidence

How to Use the Key Signature Finder

Choose Input Mode

Select Listen to detect from live audio or a file, Enter Chords to type a chord progression, or Enter Notes to pick pitch classes manually.

Provide Musical Data

In Listen mode, play music near your mic or upload a file. In Chord mode, type chords like "C Am F G". In Note mode, check the notes you hear in the song.

View Detected Key

The tool analyzes pitch distribution using the Krumhansl-Schmuckler algorithm and shows the most likely key with a confidence percentage.

Explore Results

See diatonic chords, key signature staff notation, relative/parallel keys, guitar capo suggestions, and all 24 keys ranked. Copy or export your results.

Frequently Asked Questions

How does the key detection algorithm work?

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).

How accurate is the key detection?

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.

What is the difference between relative and parallel keys?

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).

How do guitar capo suggestions work?

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).

Can I detect the key from a chord progression?

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.

Is my audio data private?

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.

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