Base64 Encoder & Decoder

It rewrites arbitrary binary data using only 64 printable characters, so it can travel through channels that only accept text: email attachments (MIME), JSON payloads, JWT parts, data URIs in CSS and HTML, and HTTP headers. It is an encoding, not encryption — anyone can decode it, so never use it to hide a secret. The cost is size: Base64 output is about 33% larger than the input.

Standard Base64 uses "+" and "/", which have their own meaning inside URLs and file names — "+" can become a space and "/" becomes a path separator. RFC 4648 §5 swaps them for "-" and "_" and usually drops the "=" padding, which is what JWTs and most APIs that put Base64 in a query string or path use. The decoder here accepts both alphabets, so you never have to say which one you pasted.

Because the data was never text. Base64 can carry any bytes — a PNG, a ZIP, a protobuf message — and rendering those bytes as characters gives you noise. If the bytes are not valid UTF-8 this tool says so and offers a download instead, so you can save the real file rather than copy a broken string.

No. Encoding uses the browser's built-in btoa/atob and TextEncoder APIs, and a file you choose is read with the File API on your own machine. There is no upload, no API call and nothing stored — you can disconnect from the network and the page keeps working.