Paste a string to validate if it is properly Base64 encoded. Get detailed diagnostics including character set analysis, padding check, and decode test.
A valid Base64 string contains only characters from the Base64 alphabet: A-Z, a-z, 0-9, + and / (or - and _ for URL-safe variant). The string length must be a multiple of 4 when properly padded with = characters.
Common issues include trailing whitespace, line breaks, or characters outside the Base64 alphabet. This validator checks all these conditions and attempts to decode the string to confirm it produces valid binary data.
Common reasons include: spaces or line breaks in the string, characters outside the Base64 alphabet (like @, #, or !), or incorrect padding. The validator will tell you exactly what's wrong.
Technically, proper Base64 requires padding to make the length a multiple of 4. However, many implementations accept unpadded strings. This validator considers unpadded strings as 'valid but missing padding.'
URL-safe Base64 replaces + with - and / with _ to avoid conflicts with URL special characters. This variant is commonly used in JWT tokens, data URIs, and filenames.
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