Fret Note

{
  "a4Used": 440,
  "asOf": "2026-10-12T01:46:28.342Z",
  "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.",
  "frequencyHz": 110,
  "fretNumber": 5,
  "instrument": "guitar",
  "midiNumber": 45,
  "notChecked": [
    "intonation, string gauge and capo-induced pitch drift on a real instrument",
    "alternate tunings where strings move by different amounts (use the tuningOffset only for whole-instrument shifts)",
    "…1 more"
  ],
  "noteFlat": "A2",
  "noteSharp": "A2",
  "octaveUp12thFretNote": "A3",
  "openStringMidi": 40,
  "openStringNote": "E2",
  "reasons": [
    "Open strings (standard EADGBE, string 1 = high E4, string 6 = low E2); each fret adds one semitone.",
    "Frequency uses equal temperament with MIDI 69 = A4."
  ],
  "source": "computed locally (open-string MIDI note + fret semitones; Hz = A4 x 2^((midi - 69) / 12))",
  "stringNumber": 6,
  "summary": "guitar string 6, fret 5: A2, MIDI 45, 110 Hz.",
  "tuningOffsetSemitones": 0,
  "verdict": "COMPUTED"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://music-production-calc.x402tookit.com/fret-note?fret=5&instrument=guitar&string=6'

# 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/fret-note?fret=5&instrument=guitar&string=6' \
  | 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%2Ffret-note
const res = await pay("https://music-production-calc.x402tookit.com/fret-note?fret=5&instrument=guitar&string=6");
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/fret-note?fret=5&instrument=guitar&string=6")
    print(res.status_code, res.text)