Base64 guides

Common Base64 Errors

Most failures come from mixing variants, altering whitespace, or decoding bytes with the wrong character set. Preserve the exact value and identify the producer's specification.

Invalid length and padding

Standard Base64 normally has a length divisible by four. Missing padding may be valid in Base64URL but rejected by a strict decoder.

Unexpected characters

Spaces, line breaks, URL escaping, and a plus sign converted to a space by form encoding are common causes. Normalize transport formatting separately from content.

Round-trip checklist

Confirm alphabet, charset, padding, and whether the value is raw payload or a complete data URL. Compare bytes with the online decoder; never paste private credentials into public tools.