Bank of Japan Exchange Rate API: Official USD/JPY Rates as JSON

Bank of Japan publishes official exchange rates — USD/JPY — the 17:00 JST spot rate and the central rate — and these are the published official rates used for tax filings, audits, and compliant invoicing in Japan, not moving market prices. This guide shows how to pull them as JSON: via a REST endpoint or the zero-dependency boj-exchange-rate npm package, with history back to 1998.

What the BOJ publishes

• USD/JPY — the 17:00 JST spot rate and the central rate.
• History back to 1998 — queryable by exact date or as a time series.
• The bank's own publication date on every response, so a rate is always citable.
• No gaps to trip over — requests for non-publication days resolve to the most recent published rates and are flagged explicitly.

The BOJ publishes one pair — but it is the pair: the official Tokyo-market record of dollar-yen, maintained since 1998.

Why official rates, not market rates

A live mid-market feed answers "what is USD/JPY trading at right now?" — the right tool for checkouts and dashboards. But accountants, auditors, and tax authorities ask a different question: "which rate were you required to use for this date?" That answer comes from the central bank's published rates, and it never changes after publication.

Get the latest rates (REST)

curl "https://allratestoday.com/api/v1/central-bank/boj/latest" \
  -H "Authorization: Bearer YOUR_API_KEY"

The response is the bank's most recent published data — every rate and the publication date. The latest rates are available on every plan, including the free tier (300 requests/month, no credit card).

The npm SDK

npm install boj-exchange-rate

import { getRate, getLatestRates } from 'boj-exchange-rate';

// One pair at the official Bank of Japan rate
const pair = await getRate('USD', 'JPY', { apiKey: 'art_live_...' });
console.log(pair.rate, pair.rate_date);

// The bank's full published table
const table = await getLatestRates({ apiKey: 'art_live_...' });
console.log(table.rate_date, table.rates.length);

Zero dependencies, TypeScript types included, and it runs anywhere fetch exists — Node 18+, Bun, Deno, and edge runtimes.

Historical rates for an invoice date

import { getRatesForDate, getHistory } from 'boj-exchange-rate';

// The official rates for an invoice date — non-publication days return
// the most recent published date, flagged via published_on_requested_date.
const day = await getRatesForDate('2026-06-30', { apiKey: 'art_live_...' });

// Time series for one pair
const series = await getHistory(
  { source: 'USD', target: 'JPY', from: '2026-01-01' },
  { apiKey: 'art_live_...' }
);

Historical dates and time series need a paid plan; the latest rates stay free.

Published vs derived pairs

If the BOJ does not print a pair directly, the API resolves it from the bank's published rates — an inverse, or a cross rate via JPY — and flags it derived: true with the method used. Official and computed values are never silently mixed, which is exactly the distinction an auditor will ask about.

FAQ

Does Bank of Japan have an official exchange rate API?

Bank of Japan publishes its official rates on its website, but not always in a developer-friendly form. AllRatesToday serves the bank's published rates as clean JSON — USD/JPY, with history back to 1998 — via REST or the boj-exchange-rate npm package. The latest table is free.

How often do Bank of Japan rates update?

Once per business day. These are published reference rates, not moving market prices — the table changes when the bank publishes a new one, and every API response carries the bank's own publication date so you can cite it.

Can I get the Bank of Japan rate for a past date, like an invoice date?

Yes. The /central-bank/boj/rates-for-date endpoint returns the official rates for any date back to 1998. Non-publication days resolve to the most recent published date and are flagged, so your audit trail stays honest. Historical dates require a paid plan; latest rates are free.