What is Base64 decoding?

Base64 decoding is the reverse of Base64 encoding. It converts a string of 64 printable ASCII characters (A-Z, a-z, 0-9, +, /) back to its original binary or text data.

What is URL-safe Base64?

URL-safe Base64 replaces + with - and / with _ so the string can appear in URLs and filenames without percent-encoding. This tool normalises URL-safe characters automatically before decoding.

Why does my Base64 string have = at the end?

The = characters are padding added to make the Base64 string length a multiple of 4. This tool adds missing padding automatically, so you can paste strings with or without it.

What does "Invalid Base64" mean?

The input contains characters outside the Base64 alphabet (A-Z, a-z, 0-9, +, /, =) or the decoded bytes are not valid UTF-8. Check for extra spaces, line breaks, or copied characters.

Is my data sent to a server?

No. All decoding and encoding runs entirely in your browser using JavaScript. Nothing is transmitted to any server.

Can this decode binary data?

The tool decodes to UTF-8 text. If the original data was binary (e.g., an image), the decoded bytes may not display as readable text and an error about invalid UTF-8 may appear.

Base64 Decoder

Name: Base64 Decoder
Availability: InStock
Author: Nham Vu

Paste a Base64 string and decode it to plain text instantly — supports standard and URL-safe alphabets, auto-padding, and Unicode.

Base64 → plain text

Alphabet Standard URL-safe

Base64 Input

Decoded Output

Copied!

Summary

Paste a Base64 string and decode it to plain text instantly — supports standard and URL-safe alphabets, auto-padding, and Unicode.

How it works

Select the Decode or Encode tab.
Paste your Base64 string (or plain text) into the input field.
Choose Standard or URL-safe alphabet if needed.
The decoded (or encoded) result updates instantly.
Click Copy to copy the result to your clipboard.
The output character count is shown below the result area.

Use cases

Decode Base64-encoded JWT payload or header to inspect the claims.
Decode Basic Auth header values (user:password) from HTTP logs.
Decode Base64 email attachments or MIME parts.
Convert URL-safe Base64 tokens used in OAuth and PKCE flows.
Decode Base64-encoded environment variables or configuration values.
Verify that a Base64 string encodes the expected data.
Decode Base64 data URIs embedded in HTML or CSS.
Decode Base64-encoded API responses or webhook payloads.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu