Current and historical exchanges rates for 120+ currencies relative to USD provided in bulk and via API. Earliest historical data is 2011-09-31.
Every hour, Currency Bot queries a currency conversion provider (currency.me.uk, formerly the Google Calculator API, and potentially a few others in the near future) collecting all the conversion rates for all currencies one-by-one, then saving them into a formatted API JSON file and pushing it to GitHub for everyone to use as an open-source API.
It's mirrored on http://openexchangerates.org with friendly Access-Control HTTP headers, so that you can load it in via AJAX with a cross-domain request without worrying about browser security restrictions.
As with all exchange rate data, accuracy can never be guaranteed when you're not paying through the teeth for the service - and when money changes currencies, everyone takes a cut (not to be trusted!) - so it's a good idea to inform people that these are for informational purposes only, something like "Converted prices/exchange rates are for informational purposes only." Feel free to say that rates come form the Open Source Exchange Rates API.
Openness: Not Open
Update: 2012-07-16. Data is not open (non-commercial restrictions). To quote from the the license page:
The Data available through the Service and the Project is released under a non-commercial license. This means that you may not resell or directly profit from, or cause any entity to profit from, direct sale or provision of the Data.
You may use the Data to build services that are informed by it inside commercial applications (for example, a currency conversion widget for shopping cart software, or to provide points of reference for statistical diagrams and graphs).
In a nutshell: You are not permitted to sell or profit directly from the Data, or by providing access to the Data; but you are permitted to use it inside commercial applications, provided that the Data itself is not the product being sold or direct cause of any profit.
Note also that the data does not originate from this project but is sourced from elsewhere. As such it's not clear what exactly its openness is. Again to quote from the license page:
Exchange rates (the "Data") are collected regularly from various free providers and sources (see list, below) in accordance with their respective robots.txt directives (if any) and Terms and Conditions. No laws or legal policies are broken in order to collect the Data. Having obeyed Terms and Conditions and related directives, the Project can and will not be held liable for legal claim or damages caused by collection, or usage by any party, of this Data.
Open Exchange Rates. Joss Crowcroft.
Retrieved 15:51, May 24, 2013 (UTC).
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