1 · Decode, in your browser
Your file is decoded with the browser’s own audio engine and mixed down to mono. It never touches a network request.
Free online key detector Beta
Detect the key and BPM of any song
Drop your tracks below. You get the musical key, the Camelot code and the tempo of every file — unlimited, without an account, and without a single byte leaving your computer.
- Nothing is uploaded
- Unlimited files
- CSV & JSON export, free
- No signup, no ads
Drop audio files here
or browse your computer — MP3, WAV, FLAC, M4A, OGG. Whole folders welcome.
Select a row to see the chromagram, the alternative keys and the harmonic mixing matches.
Play music in the room, or play your instrument. We listen for 20 seconds and analyze the recording with the exact same engine — the audio is never recorded to disk or uploaded.
Needs microphone permission — nothing is captured until you press the button.
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—confidence
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Mixes well with
Harmonic neighbours on the Camelot wheel — safe transitions from this track.
If it doesn’t sound right
The runner-up keys, in order. Relative and parallel keys share most notes, so these are the usual near-misses.
Chords in this key
The seven diatonic triads. Nearly every song in this key is built from these — the roman numeral tells you the role each one plays.
Chromagram
How much of each of the twelve pitch classes the track actually contains. The bars are the evidence behind the verdict.
Key over time
The track split into sections, each analyzed on its own. A block that disagrees with the verdict is usually a modulation, a bridge or a key change.
Beta This analyzer is new, and it is honest about what it can do. On full mixes it is solid; on isolated stems — a bass or drum track on its own — key detection gets much weaker, because a bass line plays roots without the chords that decide major from minor. Tempo can also land on the double or the half of what you tap. When a result looks off, open the row: the true answer is almost always sitting in “If it doesn’t sound right”, and the BPM has ½ and ×2 buttons.
Every file is decoded and analyzed by your own browser in a Web Worker. No upload, no account, no tracking of what you analyze.
No file needed
Tap the BPM of anything
Tap along to a rehearsal, a metronome, a record player or a song stuck in your head. Four taps is enough, and the more you tap the steadier it gets.
—BPM
At this tempo
Note lengths in milliseconds — the numbers you type into a delay or a tremolo.
Key transposer
Move a song to a key you can actually sing
Pick where the song is now and how far you want to move it. You get the new key, its Camelot code and every chord rewritten. Analyze a file above and this fills itself in.
Shift
semitones
8B
1d
The notes of the target key. Click a key to hear it.
Harmonic mixing
The Camelot wheel
Click any key. Everything that lights up will blend with it: one step around the wheel, or the same number on the other ring. Neighbours share all but one note.
Selected
C Major
8B
The outer ring is major (B), the inner ring is minor (A). Same number, different ring = relative keys: the same seven notes with a different centre of gravity.
Why this one
Everything free, including the parts others charge for
Most online key finders gate exporting, batch analysis or the whole result table behind a subscription. This one doesn’t gate anything.
| Feature | Key Detector Analyzer | Typical online analyzer |
|---|---|---|
| Key & BPM detection | Free | Free |
| Files per batch | Unlimited | Capped on the free tier |
| Download results (CSV / JSON) | Free | Paid plan |
| Camelot & Open Key notation | Free | Sometimes |
| Harmonic mixing suggestions | Yes | No |
| Key changes over time | Yes, per section | No |
| Chromagram & alternative keys | Yes | No |
| Ads | None | On the free tier |
| Account required | Never | For saving results |
| Audio leaves your machine | Never | Varies |
| Analyze what’s playing in a browser tab | With the free extension | No |
Under the hood
How the analysis works
2 · Build a chromagram
A radix-2 FFT runs over the whole track in overlapping windows. Every frame is energy-normalised first, so a loud drop can’t outvote a quiet verse.
3 · Match all 24 keys
The chromagram is correlated against the Krumhansl-Schmuckler major and minor profiles in every rotation. The best match is the key; the correlation becomes the confidence score.
4 · Find the tactus
An onset envelope is autocorrelated and comb-filtered, then an accent-asymmetry test catches the classic octave error so a 76 BPM track isn’t reported as 153.
Next step
Analyzing something you don’t have as a file?
The free Chrome extension reads the audio straight from any browser tab — YouTube, Spotify Web, SoundCloud, Bandcamp — with no microphone and no download. It adds live detection, a reference piano, and a Pro real-time YouTube transposer.
Add to Chrome — free
FAQ
Questions about the analyzer
Are my audio files uploaded anywhere?
No. Every file is decoded and processed inside your browser, in a Web Worker. Nothing is sent to a server, nothing is stored, and once the page has loaded it keeps working with the network off.
Is there a limit on how many files I can analyze?
No limit, no account, no ads. Drop a whole folder if you like — the queue runs several files in parallel and CSV or JSON export is free as well.
Which audio formats are supported?
Whatever your browser can decode. MP3, WAV, FLAC, M4A/AAC, OGG and OPUS all work in Chrome and Edge; Safari and Firefox cover most of them, with FLAC and OPUS depending on the version.
How accurate is the key detection?
It builds a chromagram of the whole track and correlates it against all 24 major and minor Krumhansl-Schmuckler profiles, then reports a confidence score and the runner-up keys. Tonal, harmonically rich material scores very high. For very percussive, atonal or modal tracks, check the alternatives — the true key is almost always the relative or parallel one right below the verdict.
What is a Camelot code?
Camelot notation maps each of the 24 keys onto a wheel of numbers and letters — C major is 8B, A minor is 8A. Tracks that share a number, sit one number apart, or share the number with the other letter will mix harmonically. The “Mixes well with” panel does that lookup for you.
Can I analyze music that’s playing instead of a file?
Yes. The Microphone tab listens to the room or to your instrument and runs the same analysis. To read audio directly from a browser tab with no microphone involved, install the free Chrome extension.
Why is it marked Beta?
Because it is new and we would rather tell you where it is weak than let you find out. Measured against a set of fully-mixed tracks with the key and tempo known in advance, it gets both right the large majority of the time. Isolated stems are the known weak spot: a bass-only or drums-only file gives the algorithm very little harmony to work with, and the key becomes a guess between closely related candidates. Full mixes are what it is built for.
Why does the BPM sometimes look doubled or halved?
Tempo lives on a ladder of metric levels — 75 and 150 BPM describe the same groove. The engine runs an accent-asymmetry test to pick the level people actually tap to, but on ambiguous grooves you may still prefer the half or double. Use the ½ and ×2 buttons on the result, or tap the tempo yourself — four taps settle it.