Question 1

How do I know if a string is Base64 encoded?

Accepted Answer

Base64 strings consist of only A-Z, a-z, 0-9, +, / and optional = padding at the end. They are usually a multiple of 4 characters. If a string looks like random alphanumeric gibberish, it's likely Base64.

Question 2

What happens if I paste invalid Base64?

Accepted Answer

The decoder will show a clear error message explaining the input is invalid. Common causes include corrupted strings, extra spaces or line breaks, or URL-safe Base64 (which uses - and _ instead of + and /).

Question 3

What is URL-safe Base64?

Accepted Answer

URL-safe Base64 replaces + with - and / with _ so the encoded string can be used in URLs without percent-encoding. Standard Base64 decoders may reject URL-safe strings — replace - with + and _ with / first.

Base64 Decoder

Base64 Input

Decoded Text

What can be decoded from Base64?