100% Client-Side

Base64 Decoder

Decode Base64 strings back to plain text or binary data

Free Client-Side No Login No Storage
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Base64 Encoder Encode text or binary data to Base64 — standard and URL-safe variants URL Decoder Decode percent-encoded URLs back to readable query strings Hex Decoder Decode hexadecimal strings back to plain text Binary Decoder Decode binary strings back to readable text

How to Use the Base64 Decoder

  1. Paste a Base64 string into the input field.
  2. Click Decode to convert back to plain text.

Supports both standard and URL-safe Base64 input. The decoder automatically handles missing padding and URL-safe character substitutions.

What is Base64 Decoding?

Base64 decoding reverses the encoding process, converting Base64-encoded ASCII text back to its original binary or text form. The decoder reads groups of 4 Base64 characters and converts them back to 3 bytes of original data.

Common Uses

  • Inspecting JWT token payloads (header and payload are Base64URL-encoded)
  • Decoding images or files embedded as data URIs
  • Debugging API responses that contain Base64-encoded fields
  • Reading Base64-encoded email attachments (MIME format)

Frequently Asked Questions

Why do I get garbled output when decoding?

The original data was binary (like an image or compressed file), not plain text. Base64 can encode any binary data — if the original wasn't text, decoding to text will show garbled characters.

Can I decode a JWT with this tool?

Yes for the header and payload — split the JWT at the dots, take the first or second part, and decode it. The signature (third part) is a cryptographic hash and won't decode to readable text.

Is Base64 decoding safe to do online?

Aya Corporation runs 100 % in your browser — no data is sent to any server. It is safe to decode sensitive Base64 strings here.

Notes from this implementation

Text out, or bytes that are not text

Decoding reverses the 4-character groups. If the original bytes were UTF-8 text, you get the text back. If they were a PNG, a gzip stream, or a hash, you get a binary mess in a text box, which is a sign to stop and download the bytes rather than to “fix” the charset.

JWT segments are Base64URL. If decode fails, restore the alphabet (- to +, _ to /) and add = until the length is a multiple of 4. A signature segment (the third piece of a JWT) decodes to raw MAC bytes, not to JSON. Seeing garbage there is correct.

Whitespace

MIME email wraps Base64 at 76 columns. The decoder should ignore those line breaks. A stray comma or a smart quote from a chat app will not be ignored. If a paste fails, it is usually one character that is not in the alphabet, not a bug in the padding math.