Base64 Validator and Inspector
Paste a string to find out if it is valid Base64 - and if not, exactly why: an invalid character (with its position), wrong padding, a length that cannot be right, mixed alphabets. Valid input is decoded so you can see whether it is text or a file, and how big it is.
How to use the Validator tool
- Paste the string to check.
- Read the verdict and the list of problems, each with its position.
- Fix the input, or open the decoded data in the right tool.
Questions and answers
How do I know if a string is Base64?
It only contains A-Z a-z 0-9 + / (or - _), its length is a multiple of 4 (with = padding), and it decodes to sensible data. Note that short words like "test" are technically valid Base64 too.
What is "impossible length"?
A Base64 string can never have a length of 4n+1 characters (without padding). One character is missing or extra - often lost when copying.
Does whitespace make Base64 invalid?
Line breaks and spaces are allowed by most decoders (MIME). The validator reports them as a warning, not an error.
Is my data uploaded to a server?
No. Every conversion on this page runs inside your browser with JavaScript. Your text and files never leave your computer, which is why it also works for private keys, contracts and photos.
Is the tool free?
Yes, free without sign-up and without limits other than your computer's memory. The site is paid for by the small ads on the left and at the bottom.