bence91 Hey there. Are you looking for historical data or trailing x?
I recently put up a JSON API where you can do XLM to fiat conversions.
https://stellar.shop/docs/get-conversion-rates
The primary reason I built it was to help price things on websites making it easy for buyers/sellers to maintain context from USD > XLM > EUR. No reason I couldn't update it to include history if that would be useful.
Let me know what type of app you're building and we can chat about options.