API & MCP

Everything a person can do on Tuning Reference (String Frequencies & Temperaments), a program or AI agent can do with the same inputs and get the identical result.

HTTP API

POST https://tonegridtuningreference.usefulweb.app/api/v1/calculate – run Tuning Reference (String Frequencies & Temperaments)
GET https://tonegridtuningreference.usefulweb.app/api/v1/tool – inputs, output schema, examples
OpenAPI 3.1: /openapi.json · /openapi.yaml
Errors: application/problem+json; 422 includes per-field errors.

Tuning Reference (String Frequencies & Temperaments)

Look up the exact frequency of every string of an instrument tuning and of a whole octave of notes for a reference pitch between A4 = 415 and 466 Hz, in equal temperament, 5-limit just intonation, Pythagorean tuning, quarter-comma meantone, Werckmeister III or Vallotti on any tonic — with the deviation of each note from equal temperament in cents. The same tables as the tuner and drone in the Tonegrid app.

Inputs of Tuning Reference (String Frequencies & Temperaments)
Field	Type	Default	Description
`instrument`	select (none, guitar/standard, guitar/dropD, guitar/halfDown, guitar/dadgad, guitar/openG, guitar/openD, guitar7/standard, bass4/standard, bass4/dropD, bass5/standard, ukulele/standard, ukulele/lowG,	"guitar/standard"	Instrument tuning
`a4`	number	440	Reference pitch A4 (Hz)
`temperament`	select (equal, just, pythagorean, meantone, werckmeister3, vallotti)	"equal"	Temperament
`tonic`	select (C, C♯, D, E♭, E, F, F♯, G, A♭, A, B♭, B)	"C"	Tonic (key the temperament is built on)
`octave`	integer	4	Octave of the note table

Example request

Guitar in standard tuning at A4 = 440 Hz

curl -X POST https://tonegridtuningreference.usefulweb.app/api/v1/calculate -H 'content-type: application/json' -d '{"instrument":"guitar/standard","a4":440,"temperament":"equal","tonic":"C","octave":4}'

Every result contains

inputs (normalised, defaults applied), summary, result (validated against the published schema), units, assumptions, sources, warnings, computedAt and links.

MCP (Model Context Protocol)

Streamable HTTP endpoint: https://tonegridtuningreference.usefulweb.app/mcp – protocol revisions 2026-07-28 (stateless) and 2025-11-25 / 2025-06-18 / 2025-03-26 (initialize handshake).
Tools: tonegrid_tuning_reference
Local stdio connector: node src/mcp-stdio.ts --tool=tonegrid-tuning-reference

{
  "mcpServers": {
    "tonegrid-tuning-reference": { "type": "http", "url": "https://tonegridtuningreference.usefulweb.app/mcp" }
  }
}