MusicReasonChords and Harmony
Build a chord from a formula
Choose a tonic and a chord quality. This tool spells every tone correctly from that formula and lets you hear it, which is the opposite direction from Chord Identifier: here you choose the structure, rather than asking what a note set could mean.
Answer and Play
Want to learn more? Chord Naming, Enharmonic Spelling, and Ambiguity
Understand
Extensions and alterations here are always explicit: choosing "dominant 7th sharp 11" never silently restores a missing tone or guesses at a spelling. A degree beyond the seventh (a 9th, 11th, or 13th) reuses the same letter name as its simple equivalent one octave down, which is why a 9th shares a letter with a 2nd and an 11th shares a letter with a 4th. This tool never claims its result is "the only correct voicing," and it makes no functional or key-context claim on its own.
Worked examples
C major 7th spells as C, E, G, B. F-sharp minor 7th spells as F-sharp, A, C-sharp, E, each degree spelled from F-sharp's own letter sequence rather than borrowed from an unrelated key. B-flat dominant 7th sharp 11 spells as B-flat, D, F, A-flat, E natural: the sharp 11 raises the chord's eleventh (normally E-flat above B-flat) by one semitone to E natural, which is why that tone is not spelled as some other enharmonic equivalent.
Method and limitations
Each formula lists scale-degree numbers with an explicit semitone offset from the root. The tool assigns each degree's letter by counting that many letter names above the root (wrapping every seven), then spells that letter with whatever accidental reaches the formula's target pitch class. Reordering the output for a different inversion changes only display order, never the underlying pitch-class set. This launch vocabulary covers common triads, sevenths, and one worked altered-extension formula; further extensions and alterations await their own specification pass.