Base64 Encoder/Decoder – Text & File, URL-Safe, MIME Line Breaks (Free Tool)

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Base64 Encoder / Decoder

A complete browser-based Base64 tool for text and files: devnestio.pages.dev/base64-tool/

Features

Text mode — encode or decode any text string
File mode — drag-and-drop or select a file to get its Base64
URL-safe mode — replaces + with - and / with _
MIME line breaks — inserts \n every 76 characters (RFC 2045)
Character count for both input and output
Copy buttons for instant clipboard copy
Zero dependencies, instant results

UTF-8 Handling

The tool correctly handles multi-byte characters (emoji, Japanese, etc.) by encoding through TextEncoder first:

function toBase64(str, urlSafe, lineBreaks) {
  const bytes = new TextEncoder().encode(str);
  let b64 = btoa(String.fromCharCode(...bytes));
  if (urlSafe) b64 = b64.replace(/\+/g, '-').replace(/\//g, '_');
  if (lineBreaks) b64 = b64.match(/.{1,76}/g).join('\n');
  return b64;
}

Decoding reverses through TextDecoder:

function fromBase64(b64, urlSafe) {
  let s = b64.replace(/\s/g, '');
  if (urlSafe) s = s.replace(/-/g, '+').replace(/_/g, '/');
  while (s.length % 4 !== 0) s += '='; // auto-pad
  const bytes = Buffer.from(s, 'base64');
  return new TextDecoder().decode(bytes);
}

Base64 Quick Facts

Property	Value
Alphabet	A–Z, a–z, 0–9, +, /
URL-safe	A–Z, a–z, 0–9, -, _
Padding	= (1 or 2 chars)
Size overhead	~33% larger than input
MIME line length	76 chars
Bits per char	6 bits → 1 char