Base64 is a binary-to-text encoding scheme that represents binary data using 64 printable ASCII characters (A-Z, a-z, 0-9, +, /). It's commonly used to embed binary data in text-based formats like JSON, HTML, CSS, and email.

URL-safe Base64 replaces + with - and / with _, making the output safe for use in URLs and filenames without additional encoding. It's defined in RFC 4648.

Base64 encodes 3 bytes of binary data into 4 ASCII characters, resulting in roughly 33% size increase. This is the trade-off for being able to represent binary data as text.

Yes. All encoding and decoding happens entirely in your browser. No data is ever sent to any server. You can verify this in the Network tab of your browser's developer tools.

Any file type — images, PDFs, documents, binaries. The file tab supports files up to 10 MB. The result includes a Data URI option that you can use directly in HTML or CSS.