Base64 turns arbitrary binary data into a string made up only of letters, digits, and a few symbols, by mapping every 3 bytes of input to 4 printable characters. That's why it's the standard way to embed images or files inside JSON, HTML data URIs, or email attachments — systems that were only designed to safely carry plain text can carry Base64 without corrupting it. This tool handles both directions, plus the URL-safe variant and files, not just plain text.
Because Base64 represents each 3 bytes of source data as 4 encoded characters, the output is roughly 33% larger than the input — that overhead is the tradeoff for making binary data safe to embed in text-only formats.
Standard Base64 uses "+" and "/" characters, which have special meaning inside URLs and file paths. The URL-safe variant swaps those for "-" and "_" instead, which is why you'll see it used in things like JWT tokens and query parameters.
Yes — pasting Base64 data (including a full data URI) into the decoder will preview it directly if it's an image or audio file, and you can save the decoded result to disk.