Bank of Sierra Leone Exchange Rate API: Official SLE (Leone) Rates as JSON

The Bank of Sierra Leone publishes the official exchange rates that accounting, tax, and customs rules in Sierra Leone reference — published official rates, not moving market prices. This guide shows how to pull them as JSON: via a REST endpoint or the zero-dependency bank-of-sierra-leone-exchange-rate npm package.

What the BSL publishes

• The daily reference rate for about 25 currencies in new leones per unit — 22.8215 per US dollar and 25.9985 per euro on the sheet dated 25 September 2026.
• A weighted-average interbank mid rate — the figure the bank's Financial Markets Department computes from the day's interbank market, and the rate Sierra Leonean customs, the National Revenue Authority and the banks convert at.
• The majors, the Gulf and the neighbours — USD, EUR, GBP, CHF, JPY, CAD, AUD and the Nordic units, SAR, AED and KWD, the rand, yuan and Hong Kong dollar, the SDR, and the CFA franc, dalasi, Guinean franc, cedi, naira, Liberian dollar and Cabo Verde escudo.
• An archive that builds forward from September 2026 — the bank keeps only the last few weeks of sheets online, so every table from our first fetch onward is kept and queryable by date.

The leone was redenominated in 2022 (1,000 old leones to one new leone, ISO code SLE), and the BSL's daily reference rate is the official figure in the new unit. The API serves that sheet, dated, for every currency the bank prints — including the regional currencies that no market feed quotes.

Why official rates, not market rates

A live mid-market feed answers "what is USD/SLE 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 Bank of Sierra Leone's published rates, and it never changes after publication.

Get the latest rates (REST)

curl "https://allratestoday.com/api/v1/central-bank/bsl/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 bank-of-sierra-leone-exchange-rate

import { getRate, getLatestRates } from 'bank-of-sierra-leone-exchange-rate';

// One pair at the official BSL rate
const pair = await getRate('USD', 'SLE', { 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 'bank-of-sierra-leone-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('2026-09-15', { apiKey: 'art_live_...' });

// Time series for one pair
const series = await getHistory(
  { source: 'USD', target: 'SLE', from: '2026-09-01' },
  { apiKey: 'art_live_...' }
);

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

Published vs derived pairs

If the BSL does not print a pair directly, the API resolves it from the bank's published rates — an inverse, or a cross rate via SLE — 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.

Reference rates from September 2026

Our archive starts on 1 September 2026, when the dollar stood at 22.80 leones; it was 22.8215 on 25 September. The bank publishes only the most recent sheets on its site and nothing older is served, so the series grows one business day at a time from here. For a past date inside the archive, one call returns the sheet published that day; weekends and holidays resolve to the last published sheet and are flagged.

FAQ

Does the Bank of Sierra Leone have an official exchange rate API?

The BSL publishes its official rates on its own site, and AllRatesToday serves the same published rates as clean JSON via REST or the bank-of-sierra-leone-exchange-rate npm package. The latest rates are free (300 requests/month); historical dates need a paid plan.

How often do Bank of Sierra Leone rates update?

Once per business day, in the Freetown afternoon, as one sheet of about 25 currencies in leones per unit. Every API response carries the sheet's own date; weekends and holidays resolve to the last published sheet.

Can I get the BSL rate for a past date, like an invoice date?

Yes, for dates from 1 September 2026 onward — the bank does not serve older sheets, so the archive starts there. The /central-bank/bsl/rates-for-date endpoint returns the sheet for any archived date; non-publication days resolve to the most recent published date and are flagged via published_on_requested_date.