Bank of Japan Exchange Rates API — boj-exchange-rate

Official Bank of Japan (Japan) daily exchange rates for Node.js and TypeScript. The published central bank rates behind tax filings, customs valuations, audits, and compliant invoicing — not market estimates, but the numbers Bank of Japan itself prints, every business day.

🚀 Why this client?

• 🏛️ Official published rates — Bank of Japan's own table, with the publisher's own rate_date on every response
• 📅 History back to 1998 — point-in-time tables and daily series for any past date
• 🔀 Published vs derived, always flagged — computed inverse/cross pairs carry derived: true, never mixed with official prints
• ⚡ Zero dependencies — pure ESM + CJS over global fetch; Node 18+, Bun, Deno, and edge runtimes
• 🔷 Type-safe — full TypeScript definitions shipped with the package
• 🧾 Compliance-grade metadata — rate_type, publication date, and source disclaimer on every response

Official rate, not mid-market: every value here is a number Bank of Japan itself published, fixed once printed and carrying the central bank's own rate_date — what filings and audits require. Need the live mid-market rate for pricing or display instead? Use the mid-market API or @allratestoday/sdk. The two can diverge by several percent.

🔑 Get your API key

Get a free API key at allratestoday.com/register — no credit card required. Latest rates are on every plan, including free.

📈 Latest published table

The image is rendered live from the keyless endpoint, so it follows the central bank's publications on npm and on GitHub alike without a new release. The same table as text is folded below for search and copy-paste: on GitHub a daily Action refreshes it whenever the central bank publishes a new table; on npm it is as of the package's publish date.

The table is filled in by the daily workflow.

📦 Installation

npm install @allratestoday/boj-exchange-rate

yarn add @allratestoday/boj-exchange-rate

pnpm add @allratestoday/boj-exchange-rate

Requires Node 18+ (global fetch); also runs on Bun, Deno and edge runtimes. Scoped mirror of boj-exchange-rate — same code, same versions.

🏁 Quick start

import { getRate } from '@allratestoday/boj-exchange-rate';

const pair = await getRate('USD', 'JPY', { apiKey: 'art_live_...' });
console.log(pair.rate, pair.rate_date); // the official Bank of Japan rate, on the central bank's own date

📚 API reference

• Latest pair rate — one pair from the latest published table
• Full published table — everything the central bank printed, in one call
• Table for a date — the official table for an invoice or filing date
• Daily time series — one pair across a date range

Latest pair rate

Free plan and up. Pairs the central bank does not print directly are resolved from its table and flagged (see Published vs derived rates below).

const pair = await getRate('USD', 'JPY', { apiKey: 'art_live_...' });

Response:

{
  bank: 'boj',
  name: 'Bank of Japan',
  rate_date: '2026-10-09',   // Bank of Japan's own publication date
  source: 'USD',
  target: 'JPY',
  rate: 158.1,
  rate_type: 'middle',
  derived: false,
  method: 'published',
  disclaimer: 'Official rates as published by the named central bank. On weekends/holidays the most recent published rate_date is returned.'
}

Full published table

Free plan and up. The complete table for the latest publication date.

import { getLatestRates } from '@allratestoday/boj-exchange-rate';

const table = await getLatestRates({ apiKey: 'art_live_...' });
console.log(table.rate_date, table.rates.length);

Response:

{
  bank: 'boj',
  name: 'Bank of Japan',
  rate_date: '2026-10-09',
  rates: [
    { "base": "USD", "quote": "JPY", "type": "middle", "value": 158.1 },
    { "base": "USD", "quote": "JPY", "type": "spot", "value": 158.34 },
    // … the rest of the published table (1 currency vs JPY)
  ],
  disclaimer: '…'
}

Table for a date

Paid plans. The official table for any date since 1998 — weekends and holidays return the most recent published date, flagged via published_on_requested_date, which is exactly the in-force rate a filing needs.

import { getRatesForDate } from '@allratestoday/boj-exchange-rate';

const day = await getRatesForDate('2026-06-30', { apiKey: 'art_live_...' });
// Optionally narrow to one pair:
const one = await getRatesForDate('2026-06-30', { apiKey: 'art_live_...', source: 'USD', target: 'JPY' });

Response:

{
  bank: 'boj',
  requested_date: '2026-06-30',
  rate_date: '2026-06-30',                // the date actually published
  published_on_requested_date: true,      // false when a weekend/holiday fell back
  rates: [ /* the full table for that date */ ],
  disclaimer: '…'
}

Daily time series

Paid plans. One resolved rate per publication date — ready for charting, revaluation runs, or audit workpapers.

import { getHistory } from '@allratestoday/boj-exchange-rate';

const series = await getHistory(
  { source: 'USD', target: 'JPY', from: '2026-01-01', to: '2026-10-09' },
  { apiKey: 'art_live_...' }
);

Response:

{
  bank: 'boj',
  source: 'USD',
  target: 'JPY',
  from: '2026-01-01',
  to: '2026-10-09',
  count: 152,
  rates: [
    // one entry per publication date
    { date: '2026-10-09', rate: 158.1, rate_type: 'middle', derived: false, method: 'published' },
    // …
  ],
  disclaimer: '…'
}

Pass { symbol: 'USD' } instead of source/target to get the raw published rows for one currency (all rate types, no pair resolution).

🗺️ Currencies covered

Bank of Japan currently publishes rates covering 1 currency against the JPY (as of the latest table):

🇺🇸 USD

🏛️ Source

The Bank of Japan publishes Tokyo-market USD/JPY reference rates each business day through its time-series statistics portal: the 17:00 JST spot rate and the central rate. These are the Bank's official record of the Tokyo interbank market, with history back to 1998.

• Publisher's own page: BOJ Time-Series Data Search — foreign exchange rates · www.boj.or.jp/en
• Publication: every business day; the exact schedule, freshness status and any current delay are on the Bank of Japan rates page
• In the API: usually by 10:15 UTC (measured over the last 9 publications). Schedule a sync at or after that time and retry hourly until rate_date moves; every response carries the same figure as available_by_utc — see when to poll
• Values are stored unmodified, with the publisher's own rate_date on every row — see the methodology

🧭 Reading the numbers

• value is always quote currency per 1 unit of base currency (base: "EUR", quote: "USD", value: 1.15 means 1 EUR = 1.15 USD).
• Bank of Japan quotes JPY per 1 unit of foreign currency (e.g. base: "USD", quote: "JPY" means JPY per one US dollar).
• Need the other way round? Ask getRate(target, source) and the API inverts or crosses for you, flagged derived: true — never divide a published rate yourself in a compliance workflow.
• rate_type tells you which of the central bank's series a row belongs to (middle here); some publishers print buy/sell or several fixings for the same pair.

🧩 ERP & accounting systems

Loading the official Bank of Japan rate into an accounting system is a supported workflow, not a hack. Step-by-step guides with the direction each system expects:

• Dynamics 365 Business Central — built-in Currency Exchange Rate Service, no code
• Xero · QuickBooks Online · SAP S/4HANA and ECC · Odoo

The same keyed endpoints return ?format=csv, ?format=xml and ?format=xlsx, and accept the key as ?api_key= on the URL for importers that cannot send headers:

curl "https://allratestoday.com/api/v1/central-bank/boj/latest?format=xml&api_key=art_live_..."

🤖 AI agents

• MCP server: npx -y @allratestoday/central-bank-mcp (stdio) or the hosted endpoint https://allratestoday.com/api/mcp — tools for official rates, history, cross-bank comparison and publication calendars
• Already using the general SDK or MCP server? Since 2026-10-01 @allratestoday/sdk 1.4+ has officialRates('boj') and @allratestoday/mcp-server 0.6+ has a get_official_rates tool — both return this source's latest table with no key, so you can add it without a second dependency
• Claude Code plugin (no key): /plugin marketplace add AllRates-Today/claude-code-plugin then /plugin install allratestoday@allratestoday — bundles both MCP servers plus an /official-rate boj ... command
• Evaluating? Agents can self-issue a trial key with no signup: POST https://allratestoday.com/api/agent/keys (send Content-Type: application/json) returns a 100-call key valid 7 days that covers the free-plan methods (latest table, pairs); dated tables and history need a paid plan. The MCP servers expose it as request_trial_key
• Machine-readable site guide: llms.txt · for-ai-agents

⚖️ Published vs derived rates

If Bank of Japan does not print a pair directly, the API resolves it from the central bank's own table and says so — official and computed values are never confused:

🛡️ Error handling

Errors are thrown as Error with status (HTTP code) and body (the API's JSON error) attached:

try {
  const pair = await getRate('USD', 'XXX', { apiKey: 'art_live_...' });
} catch (err) {
  console.log(err.message); // human-readable reason
  console.log(err.status);  // e.g. 404
}

🔷 TypeScript

Full definitions ship with the package — no @types install:

import type { LatestRates, PairRate, DatedRates, RateEntry, HistoryQuery, RequestOptions } from '@allratestoday/boj-exchange-rate';

📦 CommonJS

const { getRate } = require('@allratestoday/boj-exchange-rate');

getRate('USD', 'JPY', { apiKey: 'art_live_...' }).then((pair) => console.log(pair.rate));

💡 Quota tips

• Rates change once per business day — cache the published table locally and a small monthly quota goes a long way.
• Every request counts toward your AllRatesToday quota, shared across all AllRatesToday endpoints on your key.

📖 Methods reference

📥 Bulk data (no key)

Need the whole archive rather than an API call? The same published tables are mirrored daily as open data:

• Hugging Face: AllRatesToday/central-bank-exchange-rates — one CSV per institution (rates/boj.csv)
• Kaggle: allratestoday/central-bank-exchange-rates
• Raw JSON on GitHub: https://raw.githubusercontent.com/AllRates-Today/central-bank-exchange-rates/main/data/boj/latest.json

🔗 Links

• Website: allratestoday.com
• Bank of Japan rates page — live table, publication cadence, FAQ
• All central bank sources
• Download central bank rates — every bank's latest table and history as Excel, CSV or JSON
• Package docs on the site · ERP integration guides
• API documentation · Interactive reference · Methodology
• Register (Free) · Dashboard · Pricing
• Status
• Postman collection
• ChatGPT app — ask ChatGPT for live and official central bank rates
• GitHub

📜 License

MIT