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Base64 Decoder

Decode Base64 encoded text.

How to Use Base64 Decoder

1

Paste the Base64 string into the input box - an Auth header, a data URI payload or a token segment.

2

Click the "Process" button to decode it and display the original text in the output panel.

3

If the result still looks encoded, run it through again, since the data may have been encoded twice.

4

Copy the decoded text with one click, or download it as a .txt file to examine it in full offline.

Features

100% free with no sign-up and no limit on the length of the string
Decodes standard Base64 and the URL-safe Base64 variant used in JWTs
Handles missing or extra padding so slightly malformed input still works
Reports invalid characters instead of silently discarding data
Copy the decoded output in one click or download it as a .txt file
Runs in your browser, so tokens and credentials are never uploaded or stored

Frequently Asked Questions

Yes, it is completely free and unlimited, with no account required and no watermark on the output.
The decoding happens entirely in your browser, so the string is never transmitted to our servers or written to disk. That said, treat any real credential you paste as exposed if your machine is not trusted, and rotate it if it was ever shared insecurely.
Check for characters that do not belong, such as stray spaces, line breaks in the middle of the string or a truncated payload. Padded and unpadded input both work here, so a missing equals sign is usually not the problem.
Yes. The header and payload of a JWT use URL-safe Base64, which this tool also supports. You will see the claims and the exp timestamp, but remember that decoding is not verification - a token is only valid if its signature checks out.

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About Base64 Decoder

Every now and then a string arrives that you simply cannot read: a blob in a CSS data URI, the value in an Authorization header, or the middle section of a JWT token. Those are all Base64, and decoding them turns an unreadable wall of characters back into the text or structure that was hidden inside it.

Authentication is the most common reason people end up here. An HTTP Basic Authorization header looks like a single unbroken run of letters and equals signs, and if a request keeps returning 401 Unauthorized, decoding it shows you the exact username:password pair being sent - which immediately reveals the trailing space, the wrong colon, the stale password or the basic-auth prefix that was never stripped out. A JSON Web Token is a related case: the header and payload are Base64url encoded, and decoding the payload shows you the claims and their expiry timestamps without any verification.

Data URIs are the other common one. When an image or font is embedded in a file you receive, the payload after the comma is Base64 and decoding it reveals the original data, or at least its opening characters. Data can also be encoded more than once, so if the first result still looks encoded, decode it again. Invalid characters are reported rather than silently dropped, which makes it a useful way to find a corrupted or truncated payload.

When to Use This Tool

  • Inspecting an HTTP Basic Authorization header that keeps returning 401
  • Reading the claims and expiry inside a JSON Web Token
  • Decoding the payload of a data URI embedded in CSS or HTML
  • Reversing a Base64 string you generated and checking it round-trips correctly
  • Finding out why a payload is malformed by spotting the invalid character