To convert a string in base64 format and back to original text you may use the calculators below.
Base64 encoding algorithm converts input string to characters sequence, which has digits from 0 to 9, letters from a to z, capital letters from A to Z and two special symbols: + (plus) and / (slash). Latter two symbols cannot be used in web URL. You may change these two symbols to something else by passing desired replacement in the Special symbols replace parameter.
The calculator transforms input string in UTF8 characters array and then perform encoding as described in Mozilla Developer Network article