Base64 Encode / Decode

No. Encoding and decoding run entirely in your browser using JavaScript. Nothing you paste here leaves your device, which is why this tool also works offline once the page has loaded.

Standard Base64 uses + and / , both of which have meaning inside URLs. The URL-safe alphabet (RFC 4648 §5) replaces them with - and _ so the result can be dropped into a query string or path segment unescaped. JWTs use this variant.

Base64 input must have a length that is a multiple of four once padding is accounted for, and may only contain characters from the chosen alphabet. Whitespace and line breaks are stripped automatically, but stray characters will report an error rather than return partial output.