How to Base64 Decode Text

Problem

You have received a Base64-encoded string and need to recover the original plain text or binary data.

Prerequisites

• Understanding of Base64 alphabet
• Ability to recognize padding characters

Steps

1. 1. Inspect the Base64 string

   Confirm the string only contains valid Base64 characters (A-Z, a-z, 0-9, +, /) and optional = padding. Remove any whitespace or line breaks that may have been inserted for readability.

   Input

   SGVsbG8sIFdvcmxkIQ==

   Output

   clean string

2. 2. Decode the string

   Pass the cleaned string to a Base64 decoder. The decoder maps each character back to a 6-bit value, concatenates the bits, and splits them into 8-bit bytes.

   Input

   SGVsbG8sIFdvcmxkIQ==

   Output

   Hello, World!

3. 3. Interpret the result

   If the original data was text, display it as text using the correct character set. If it was binary, save it as a file or inspect the bytes. A garbled result usually means the wrong charset was assumed.

   Input

   SGVsbG8sIFdvcmxkIQ==

   Output

   Hello, World!

Expected result

The original text or binary data, identical to what was encoded before.

Common errors

Decoding fails with 'invalid length'

The string is not a multiple of 4. Add the missing = padding characters or re-encode the source.

Output is garbled or shows replacement characters

The original data was binary or used a different character set. Decode as bytes and inspect the raw output.

Troubleshooting

• Strip all whitespace before decoding.
• If the string came from a URL, replace - with + and _ with / (URL-safe Base64) first.

Security limits

• Decoding Base64 reveals the original data instantly. Do not treat Base64 as a security barrier.