Here is an interactive Base64 Encoder/Decoder. You can enter any (standard) text in the Source text area and the base64 encoded value will be generated for you and likewise any Base64Encoded text in the Encoded area and the Decoded Text will be produced for you.
Be careful to only use standard Characters for consistent results (not extended international characters).
Exact copies including spaces and carriage returns are required to get identical results.
All the work is done in your browser, so I do not have access to the data you enter.
If you save the data in a text file, be sure to save plain text (notepad etc.) rather than a wordprocessor that might change or add characters.