Base64エンコード/デコード

Base64 represents binary or text data using just 64 printable ASCII characters (A-Z, a-z, 0-9, plus + and /), encoding every three bytes as four characters. That keeps data intact when it travels through systems that were built for text rather than raw bytes.

You see it everywhere: data URLs that embed an image directly in HTML or CSS, email attachments (MIME), the header and payload of a JSON Web Token, HTTP Basic authentication headers, and many API fields that need to carry binary data as a plain string.

This tool encodes text to Base64 and decodes Base64 back to text, choosing the direction automatically. It is UTF-8 safe, so accents, emoji and other Unicode characters survive the round trip without corruption, which the naive built-in browser functions do not guarantee on their own.

It is important to know what Base64 is not: it is an encoding, not encryption. Anyone can decode it instantly, so it provides zero security. Never use it to hide passwords, tokens or secrets. Its job is safe transport and representation, not confidentiality.

Base64 also has a size cost. The encoded output is about 33 percent larger than the original, because four characters stand in for every three bytes. That trade-off is usually worth it for compatibility, but it is why you would not Base64-encode large files when a real binary channel is available.

Everything runs in your browser, so the text you paste is never uploaded. To turn an image file into a Base64 data URL instead of plain text, use the dedicated Image to Base64 tool.