Runs locally in your browser

Base64 Decoder

Decode Base64 back into readable UTF-8 text so you can inspect tokens and payloads. Decoding never leaves this browser tab.

Input

Output

Paste a Base64 blob from a JWT fragment, a data URI, or a log line and recover the original UTF-8. This page only decodes.

atob and TextDecoder run locally. Invalid alphabets surface an error instead of sending the blob elsewhere.

How to use

Whitespace around the blob is trimmed first. The decoder then maps Base64 to bytes and interprets those bytes as UTF-8.

Broken padding or characters outside the alphabet fail fast. URL-safe Base64 with minus and underscore may need a swap before decode.

JWT payload peek
The middle segment of a JWT is Base64URL. After a character swap you can read the JSON claims as text.
Log token
A config value that looks like random ASCII often decodes to a readable username or JSON blob.

Why do I see Invalid Base64?

The string has characters outside the alphabet or broken padding. Trim and check plus, slash, and equals.

Can this decode images?

It decodes to UTF-8 text. Binary image bytes will look garbled in the text box.

Is decode the reverse of the encoder on this site?

Yes for standard Base64 of UTF-8 text produced by the companion encoder.

Is the blob uploaded?

No. Decoding stays in this tab.