Base64 Validator
Check whether a string is valid Base64, and see exactly why if it isn't. Hitting decode errors? Read common Base64 errors and fixes.
Base64 Validator — FAQ
What makes a string valid Base64?+
It must use only the Base64 alphabet (A-Z, a-z, 0-9, "+" and "/", or "-" and "_" for the URL-safe variant), have a length that is a multiple of 4 for standard Base64, and use "=" padding only at the end.
Why did my Base64 string fail validation?+
The most common causes are: extra whitespace or line breaks copied by accident, a mix of standard and URL-safe characters, missing "=" padding, or the string being truncated.
Does this tool tell me what the decoded content is?+
No — this tool only checks whether the string is structurally valid Base64. Use the Base64 Decode tool to see the actual decoded output.
Can valid Base64 still decode to garbage?+
Yes. Any string that follows the Base64 alphabet rules will decode to some sequence of bytes, but those bytes are only meaningful if the original data made sense — validity does not guarantee the content is what you expect.