Base64 Decoder
Convert Base64-encoded strings back to readable plain text with UTF-8 support.
More Base64 Tools
What is the Base64 Decoder?
Base64 decoding reverses the encoding process — converting ASCII Base64 characters back into the original binary data. The algorithm maps each Base64 character to its 6-bit value, concatenates these into a bitstream, then splits into 8-bit bytes to reconstruct the original data. This decoder correctly handles UTF-8 multi-byte sequences, restoring characters that span multiple bytes (accented letters, CJK characters, emojis) to their original form.
How to use the Base64 Decoder?
- Paste a Base64-encoded string into the input area.
- Click 'Decode' to convert it back to the original plain text.
- If the string is invalid Base64, an error message explains what went wrong.
- The decoder handles UTF-8 encoded content correctly, restoring multi-byte characters and emojis.
- Click 'Copy' to copy the decoded text to your clipboard.
Frequently Asked Questions
What characters are valid in Base64?
Standard Base64 uses A-Z, a-z, 0-9, +, and / (64 characters total). The = character is used for padding at the end. Base64URL variant uses - and _ instead of + and / for URL-safe encoding.
Why does my Base64 string fail to decode?
Common causes: extra whitespace or line breaks in the string, invalid characters (anything outside the Base64 alphabet), or incorrect padding. Remove any surrounding quotes, trim whitespace, and ensure the string length is a multiple of 4.
Can I decode Base64URL strings?
This decoder handles standard Base64. For Base64URL strings (using - and _ instead of + and /), replace those characters before decoding: replace - with + and _ with /, then add = padding if needed.
Is decoding safe for sensitive data?
Yes. All decoding happens locally in your browser. No data is transmitted to any server.