🎼 Key Signature Detector
Professional music theory tool that analyzes note collections to determine the most probable key signatures. Features smart note parsing, major/minor key detection, confidence scoring, and educational explanations for musicians, composers, and music students.
Your Result:
Notes: C, D, E, F#, G, A, B
Key signature detection example preview
G Major
E Minor
🎯 Circle of Fifths Position
G Major/E Minor is located at the 1 o'clock position on the Circle of Fifths, containing one sharp (F#).
How to Use This Key Signature Detector
How to Use the Key Signature Detector
📝 Step 1: Enter Your Musical Notes
Input the notes you want to analyze in the Musical Notes field. The tool accepts various formats:
- Letter names: C, D, E, F, G, A, B
- With sharps: C#, D#, F#, G#, A#
- With flats: Db, Eb, Gb, Ab, Bb
- Mixed format: C, D#, Eb, F, G, A, Bb
Separate notes with commas, spaces, or mix both. The tool automatically parses and normalizes your input.
⚙️ Step 2: Choose Analysis Options
Select your preferred analysis depth:
- Basic: Shows only the most likely major and minor keys
- Detailed: Displays all possible keys with confidence percentages
- Educational: Includes music theory explanations and learning tips
Enable modal analysis to explore church modes and Circle of Fifths visualization for educational context.
🎼 Step 3: Analyze and Review Results
Click "Detect Key Signatures" to process your notes. The results show:
- Primary keys: Most likely major and minor key signatures
- Confidence scores: Percentage indicating detection certainty
- Sharp/flat count: Number of accidentals in each key
- Circle of Fifths position: Educational context for key relationships
Use the copy button to save results for reference or share with other musicians.
💡 Pro Tips for Best Results
- Include at least 5-6 notes for reliable detection
- When analyzing melodies, include the most prominent or repeated notes
- For chord progressions, input all unique notes from the chords
- Use the educational mode to learn about key signature relationships
How It Works
How Key Signature Detection Works
- Note Parsing and Normalization
The tool parses your input notes and converts them to a standardized format, handling both sharps and flats while recognizing enharmonic equivalents (like C# and Db).
- Circle of Fifths Analysis
Using the Circle of Fifths, the algorithm identifies which major and minor key signatures contain all or most of your input notes. Each key signature has a specific pattern of sharps or flats.
- Pattern Matching and Scoring
The system calculates confidence scores based on how well your notes match each possible key signature. Perfect matches (all notes in the key) receive higher scores than partial matches.
- Major and Minor Key Detection
Since relative major and minor keys share the same notes, the tool presents both options. For example, C major and A minor both contain the same seven notes with no sharps or flats.
- Modal Analysis (Optional)
When enabled, the tool also checks for church modes (Dorian, Phrygian, Lydian, etc.) that might fit your note collection, providing a more comprehensive harmonic analysis.
- Educational Context
Results include Circle of Fifths positioning, accidental counts, and theoretical explanations to help users understand the relationships between different key signatures.
🎵 Music Theory Foundation
Key signatures indicate which sharps or flats are used consistently throughout a piece of music. The Circle of Fifths organizes these signatures in a logical pattern where each step clockwise adds one sharp, and each step counterclockwise adds one flat.
When You Might Need This
- • Analyze chord progressions to determine the underlying key signature
- • Identify key centers in jazz improvisation from played notes
- • Determine appropriate key signatures for original compositions
- • Analyze melody lines to find compatible backing keys
- • Music students learning to recognize key signatures by ear
- • Composers working on modulation between different keys
- • Band members figuring out the key of a song from sheet music
- • Music teachers demonstrating Circle of Fifths relationships
- • Transcribing music and need to identify the home key
- • Analyzing scale patterns and their corresponding key signatures
Frequently Asked Questions
How accurate is the key signature detection?
The accuracy depends on the completeness of your note collection. A full scale or significant portion provides 90-95% accuracy, while partial note sets may suggest multiple possible keys. The tool shows confidence levels to help you assess reliability.
Can this tool distinguish between major and minor keys?
Yes, the tool analyzes both major and minor key possibilities. Since relative major and minor keys share the same notes (like C major and A minor), both will be suggested with equal confidence when the complete scale is provided.
What note formats are supported for input?
The tool accepts various note formats: letter names (C, D, E), sharps (C#, F#), flats (Db, Bb), and mixed formats. Notes can be separated by commas, spaces, or mixed. Both American (B) and European (H) notation styles are recognized.
Does the tool handle modal scales and church modes?
When modal analysis is enabled, the tool can identify Dorian, Phrygian, Lydian, Mixolydian, and other church modes. This is particularly useful for jazz, folk, and contemporary music that uses modal harmonies beyond traditional major/minor.
Can I use this for atonal or chromatic music?
The tool works best with tonal music based on traditional key signatures. For highly chromatic or atonal music with all 12 notes, the analysis may suggest multiple keys or indicate no clear tonal center. It's designed for conventional Western music theory.