music21 vs Mido

These overlap only where MIDI files are involved. music21 is about music — keys, chords, counterpoint, notation. mido is about MIDI — bytes, messages and ports.

Side by side

Where they actually differ

They model different things

music21 represents scores: notes with pitch spelling, measures, key signatures, parts, articulations. mido represents MIDI events: note-on, note-off, control change. A C♯ and a D♭ are different objects in music21 and the same byte in mido — which tells you exactly which one understands music.

music21 can answer musical questions

Key detection, Roman numeral analysis, chord identification, interval arithmetic and corpus search are built in, alongside a large bundled corpus. Nothing in mido comes close, because that is not what mido is for.

mido is the one that talks to devices

Live input and output, port management, SysEx. If a controller or synth is in the picture, music21 cannot help.

Weight is a real consideration

music21 is a large dependency with a substantial import time. For a script that just needs to write a MIDI file, mido is a far lighter choice — and for a musicology project, music21’s weight is the price of everything it gives you.

Which should you choose?

Choose music21 when…

• You are analysing harmony, key or structure
• You work with MusicXML or notation
• You want a bundled corpus to study
• You are generating music that respects theory

Choose Mido when…

• You are sending or receiving live MIDI
• You want a small, fast dependency
• You need exact control over MIDI bytes
• You are building a device-facing tool

music21 cheat sheet → · All Python music libraries →

← All comparisons