# Currency Converter

> Convert an amount into several currencies at ECB euro reference rates, with rate date and source. Converts an amount between the 30 currencies of the European Central Bank’s daily euro foreign exchange reference rates – into several target currencies at once, at the latest rates or those of a past date. Cross rates are calculated via the euro; every result shows the rate, the inverse rate, the reference date and the source.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://currencyconverter.usefulweb.site/ (interactive tool at https://currencyconverter.usefulweb.site/tool)
- JSON API: POST https://currencyconverter.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://currencyconverter.usefulweb.site/api/v1/tool)
- OpenAPI: https://currencyconverter.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://currencyconverter.usefulweb.site/mcp - tool `currency_converter`

## Inputs
- amount (number, required): Amount
- from (text, required): From currency - ISO code, e.g. EUR, USD, GBP, CHF, JPY.
- to (text, required): To currencies - One or more ISO codes, comma-separated, or "all".
- date (date): Rate date - Optional: use the reference rates of this date (the last publication on or before it). Empty: latest rates.

## Method
- Rates come from the ECB’s daily reference-rate file (eurofxref-daily.xml) or, for past dates, from the ECB Data Portal (dataset EXR, daily series D.<currency>.EUR.SP00.A). They are cached per day; the daily file is re-checked at most hourly until the day’s rates (around 16:00 CET) are available.
- All ECB rates are quoted as units of currency per 1 euro, so a cross rate is rate(to) ÷ rate(from); converting X from A to B = X × rate(B) ÷ rate(A). Rates are shown with 6 significant digits; amounts are rounded half away from zero to the currency’s minor units (0 for JPY, KRW and ISK).
- For a date without a publication (weekends, TARGET holidays) the last earlier publication is used and named.
- Reference rates are published for information only. Card schemes, banks and exchange offices use their own rates and add fees, so the amount you actually pay or receive will differ.

## Limits
- ECB reference rates are not transaction rates. For a real payment, check your provider’s rate and fees.