MIDI Chord Detector - Name the Chords in Each Bar of a MIDI File

Upload a MIDI file and this tool reads it in your browser, groups the notes bar by bar, and names the chord in each bar. It is a fast way to see the harmony of a song, a loop, or your own keyboard recording. No file ever leaves your device.

What the MIDI Chord Detector does

A MIDI file stores notes, not chord names. A pianist can hear the harmony, but reading it back from a piano roll takes time, especially across many bars. This detector closes that gap. It opens your file with the @tonejs/midi library, reads every track, and groups notes by the bar they start in, using the file’s own tempo map and time signature. For each bar it collects the pitch classes and matches them against chord formulas, then prints a table with the bar number, the chord name and the notes found. You get the whole song’s harmony at a glance, ready to copy into a lead sheet or a lesson plan.

Why bar-by-bar detection works well

Most music changes chord once per bar, or once every two bars, so the bar is the natural unit for harmony. Grouping by bar also forgives short passing notes, because a single extra note does not usually change the winning formula when the chord tones dominate. The detector uses the time signature stored in the file, so a song in 3/4 groups three beats per bar and a song in 4/4 groups four. If your file has several tracks, all tracks are combined, which means a bass line on one track and chords on another are read together, exactly as they sound. That combined reading is usually more accurate than reading one track alone.

How to use the detector

Click the file button and choose a file ending in .mid or .midi. Press the detect button. The summary line shows the track count, the total note count, the time signature and the number of bars that contain notes. The table below lists every bar with notes, in order. Start with a short, simple file if you are new to MIDI, such as a four-bar loop with block chords. Check the first bar by ear: if the table says C major and you hear C major, the rest of the table is probably right too. You can then work through the song bar by bar with confidence.

Reading tricky bars

Some bars will look odd, and that is normal. A bar with a melody full of passing notes may show an approximate chord, because the detector counts every note that starts in the bar. A bar where the chord changes halfway through will show the chord with the most notes, and the second chord may be hidden. In both cases, look at the notes column: it tells you exactly what the detector saw. If you need finer detail, split the file into shorter sections, or use a version of the file with the melody on a separate track that you can remove. Jazz and classical files with rich harmony may need this kind of care, while pop loops usually read cleanly.

Uses for musicians, teachers and producers

Musicians can transcribe a song’s chords in minutes instead of hours, then learn it on their own instrument. Teachers can turn a student’s MIDI recording into a chord chart for the next lesson. Producers can check that a loop pack’s harmony matches the key of their track before they build a song around it. Songwriters can test chord ideas by playing them on a keyboard, exporting MIDI, and reading the resulting progression back as names. Because the tool runs entirely in the browser, it also works for private or unreleased material that you would not want to upload anywhere.

Privacy and limits

Your MIDI file is parsed on your own device. Nothing is sent to a server, stored, or shared, and closing the page removes the file from memory. The detector names chords from pitch classes, so it does not know about inversions, voicings or the key of the song: it names the chord, and you decide how it fits the music. Very dense files, such as full orchestral scores, may produce approximate names in busy bars. For best results, use files with clear chord parts and a correct time signature.

MIDI Chord Detector – Name the Chords in Each Bar of a MIDI File