Key Shift

{
  "asOf": "2026-10-12T01:46:28.605Z",
  "capoChoice": null,
  "capoOptions": [
    {
      "capo": 0,
      "openFriendly": true,
      "shapeKey": "G major",
      "signature": "1 sharp"
    },
    {
      "capo": 1,
      "openFriendly": false,
      "shapeKey": "F# major",
      "signature": "6 sharps"
    }
  ],
  "degraded": false,
  "disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
  "fromKey": "Eb major",
  "fromRelativeKey": "C minor",
  "fromSignature": "3 flats",
  "notChecked": [
    "modulation style: a key change can also be a pivot chord or truck-driver lift, not just a straight shift",
    "the vocal or instrument range in the new key",
    "…1 more"
  ],
  "reasons": [
    "The new tonic is the old pitch class plus the shift; the spelling with the fewest sharps or flats is used, and a tie follows the direction of the shift (or your prefer).",
    "The relative key shares the key signature: relative minor is a minor third below a major tonic, relative major a minor third above a minor tonic."
  ],
  "relativeKey": "E minor",
  "semitonesShifted": 4,
  "source": "computed locally (pitch class + semitones; spelling with the fewest accidentals in the key signature)",
  "summary": "Eb major up 4 semitone(s) is G major (1 sharp); relative E minor.",
  "toFifthsPosition": 1,
  "toKey": "G major",
  "toMode": "major",
  "toSignature": "1 sharp",
  "verdict": "COMPUTED"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://music-production-calc.x402tookit.com/key-shift?key=Eb&semitones=4'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://music-production-calc.x402tookit.com/key-shift?key=Eb&semitones=4' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fmusic-production-calc.x402tookit.com%2Fkey-shift
const res = await pay("https://music-production-calc.x402tookit.com/key-shift?key=Eb&semitones=4");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://music-production-calc.x402tookit.com/key-shift?key=Eb&semitones=4")
    print(res.status_code, res.text)