Question 1

Why do I get a "not valid UTF-8" error when the Base64 itself looks fine?

Accepted Answer

Those are two separate failure points. First the tool checks whether your input is even valid Base64 syntax (right alphabet, correct padding) — that's the "Invalid Base64" error. If it passes that check, the resulting bytes still have to form valid UTF-8 text to be displayed; if you paste the Base64 of an image, a compressed file, or otherwise non-text binary data, decoding succeeds but the bytes aren't valid UTF-8, so you get this second, different error instead of garbled output.

Question 2

Can I decode Base64 back into an image?

Accepted Answer

No — decoded bytes are always interpreted as UTF-8 text here, by design. If you paste an image's Base64 data, you'll get the "not valid UTF-8" error above rather than an image preview, since this tool is scoped to text only.

Question 3

Does extra whitespace or line breaks in my Base64 string cause an error?

Accepted Answer

No — ordinary spaces, tabs, and line breaks are ignored automatically before decoding (this is part of the Base64 spec's "forgiving" decode behavior). It's only characters outside the Base64 alphabet — anything other than A-Z, a-z, 0-9, +, /, and = padding — that will trigger an error.

Question 4

What is the difference between Base64 and the Base64URL used in things like JWTs?

Accepted Answer

Base64URL is a small variant that swaps two characters — "+" becomes "-" and "/" becomes "_" — and usually drops the "=" padding, specifically so the result is safe to use inside a URL or filename without further escaping (standard Base64's "+" and "/" are not URL-safe). This page decodes standard Base64; if you're working with a JWT specifically, use the JWT Decoder instead, which already handles the URL-safe variant.

Base64 Decoder

Unicode Safe

Clear Error Messages

Handles Large Text

Frequently Asked Questions