Base64 represents bytes with printable characters so binary data can travel in places such as JSON fields or email bodies. It is an encoding, not encryption: anyone can decode it.
Try a short known sample and decode it back to the same bytes. If you start with text, specify the character encoding—usually UTF-8—before Base64 encoding. Check whether the destination expects the standard alphabet, a URL-safe variant, or padding. The encoded output is typically larger than the input, so large files are often better sent as files or streams.
Do not paste secrets into a public encoder just because the output looks unreadable. See RFC 4648 for the format.
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