Base64 is a binary-to-text encoding scheme that represents binary data in an ASCII string format by translating it into a radix-64 representation. It is commonly used to encode data that needs to be stored and transferred over media designed to deal with textual data, for example in email (MIME) or within JSON/XML.

Valid Base64 strings (standard) only contain characters A-Z, a-z, 0-9, +, /, and = for padding. The length must be a multiple of 4 (if padded), and padding (=) can only appear at the end (1 or 2 characters). This tool checks those rules instantly.

Base64URL (URL-safe Base64) is a variant that replaces + with - and / with _, making it safe for use in URLs and filenames without additional percent-encoding. Padding (=) is often omitted but still allowed. This tool lets you switch between standard and URL‑safe validation.

The equals sign is padding to make the string length a multiple of 4 bytes. When the original binary data length is not a multiple of 3 bytes, one or two padding characters are added. This is normal and part of the Base64 specification.

Strictly, Base64 should not contain whitespace. However, many decoders tolerate spaces, tabs, or newline characters. This validator is strict by default; whitespace will make the string invalid. You can use the Clear button to remove accidental spaces.

Yes, for standard Base64 the character count (excluding optional padding handling) should be a multiple of 4. If the string is valid but missing padding, many decoders still accept it. This tool accepts both padded and unpadded strings for URL‑safe mode, but flags incorrect padding in strict mode.