# Scale, Chord and Fretboard Finder

> Notes, intervals and fretboard positions of any scale or chord — or name the chord you play. Spells a scale, mode or chord on any root with correct note names and intervals, marks every position on a guitar, 7-string, bass or ukulele neck in the tuning you choose, lists easy chord shapes and the diatonic chords of a key, or names the chord formed by a set of notes (including inversions). The same theory engine as the Fretboard tab of the Tonegrid app.

Part of usefulweb.app (https://usefulweb.app/). Part of [Tonegrid](https://tonegrid.usefulweb.app/) (ownerApp: tonegrid). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://tonegridscalechordfinder.usefulweb.app/ (interactive tool at https://tonegridscalechordfinder.usefulweb.app/tool)
- JSON API: POST https://tonegridscalechordfinder.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://tonegridscalechordfinder.usefulweb.app/api/v1/tool)
- OpenAPI: https://tonegridscalechordfinder.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://tonegridscalechordfinder.usefulweb.app/mcp - tool `tonegrid_scale_chord_finder`

## Inputs
- mode (select): What do you want?
- root (select): Root note
- scale (select): Scale or mode - Used when showing a scale.
- chord (select): Chord type - Used when showing a chord.
- notes (text): Notes to name (lowest first) - Used when naming a chord: note names separated by spaces, the bass note first. Octave numbers are optional.
- tuning (select): Instrument and tuning
- frets (integer): Frets to show

## Method
- Scales and chords are interval formulas (1, b3, 5, b7 …). The pitch of each note is the root plus the interval in equal-tempered semitones; its name uses the letter that matches the interval’s degree, so a third is always spelled with the third letter above the root (F major contains B♭, D♭ major contains G♭, a diminished seventh may need a double flat).
- Fretboard positions: every fret of every string whose pitch class belongs to the formula, from standard open-string pitches of the chosen tuning. The ukulele’s standard tuning is re-entrant (the G string is the high G4).
- Chord shapes: a four-fret window is slid up the neck to fret 15; each string is not played, open or fretted with a chord tone. A shape is kept when the sounding strings are adjacent, the lowest note is the root, every chord tone sounds (a perfect fifth may be left out of four- and five-note chords) and at most four fingers are needed, one of which may barre the lowest fret. Shapes are ranked by fret span, position, muted strings and finger count.
- Naming a chord: every note is tried as the root against 20 chord formulas; exact pitch-class matches come first, inversions are written as slash chords (C/E) with the first note as the bass, and four-note chords may be recognised without their fifth.

## Limits
- Chord shapes are generated by rules, not taken from a chord book: they are playable for most hands but not always the fingering a teacher would choose. Enharmonic spelling follows the chosen root (pick E♭ rather than D♯ for flat keys).