
Exchange rates and currency conversion.
Currencylayer API is a free Currency Exchange API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Free and startup-friendly currency converter JSON API for real-time and historical exchange rates - reliable and accurate, supporting 168 world currencies.
Details from currencylayer.com.

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The Currencylayer API is provided by Currencylayer (currencylayer.com). Free and startup-friendly currency converter JSON API for real-time and historical exchange rates - reliable and accurate, supporting 168 world currencies.
Yes. The Currencylayer API is listed in the Currency Exchange category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Currencylayer API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Currencylayer API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Currencylayer API is served over HTTPS, so it's safe to use in production.