Base64 decode

How to decode Base64

To decode Base64, paste the string into the input box with Base64 to text selected. The original text appears in the output box immediately. Standard and URL-safe alphabets are accepted, missing padding is tolerated and the bytes are read as UTF-8. Everything runs in your browser, so the string you paste is never uploaded.

What decoding does

Base64 groups the original bytes in threes and writes each group as four characters from a 64-character alphabet. Decoding reverses that: each character is turned back into 6 bits, the bits are regrouped into bytes and, if the bytes are text, they are read as UTF-8. For example, SGVsbG8= decodes to Hello.

Decoding examples

Why decoding fails

• Characters outside the alphabet. Only A-Z, a-z, 0-9, + and / (or - and _ in the URL-safe form) are valid, plus the = padding.
• Wrong length. A valid Base64 string, once padded, has a length that is a multiple of four.
• The result is not text. If the Base64 holds an image or a PDF, the output is unreadable symbols; use the file section to download it instead.
• Copy errors. A missing character or an extra space breaks the tail of the string.

Recognising what is inside

You can often guess a file type from the first characters of its Base64. Text that begins with eyJ is usually JSON (a JWT part), and the table below shows the start of common file types.

Common file signatures in Base64

Private by design

The conversion runs in your browser. What you type, paste or drop is never uploaded, which matters when the text holds tokens, personal data or internal files.