What is Base64?
Base64 is an encoding that represents binary data with only 64 safe characters: letters, digits, + and /. It lets you carry any content through channels designed for text: email attachments, data: images embedded in CSS, HTTP authentication headers, JWT tokens and more.
Keep in mind that Base64 is not encryption. Anyone can decode a Base64 string; it does not protect confidential data.
Base64 vs Base64URL
The Base64URL variant replaces + with - and / with _, and drops the trailing = padding, so the result can be used in a URL or a file name. It is the format used by JWT tokens. The decoder accepts both variants.
Why Base64 makes data bigger
Every 3 bytes become 4 characters, so encoded content is about 33% larger than the original.
FAQ
Why do accented characters break in other tools?
Many tools encode text as Latin-1. This one converts text to UTF-8 first, the web standard, so accents, non-Latin scripts and emojis always round-trip correctly.
What are the “=” signs at the end?
They are padding characters that make the string length a multiple of 4. They are optional in the Base64URL variant.