Base64 carries bytes as text; it does not hide secrets
Base64 is useful when a text channel needs to carry byte data. Its alphabet changes how the data looks, not who can understand it or whether it becomes smaller.
Count bytes before characters
Standard padded Base64 represents each 3 bytes using four characters, completing the final group with = when needed. Its length is 4 times the byte count divided by 3, rounded upward.
A single character can occupy more than one UTF-8 byte. A short Arabic string can therefore produce more encoded characters than a Latin string with the same letter count.
References: RFC 4648 — Base encodings, padding and security considerations
Encoding provides no confidentiality
Someone holding the encoded value can normally decode it without a secret key. Base64 is not a way to protect a password or conceal information inside a shared link.
Give the output the same sensitivity as the original. Preventing others from reading data requires an appropriate security mechanism, not a different textual alphabet.
References: RFC 4648 — Base encodings, padding and security considerations
Know what the decoded bytes should be
This tool encodes text as UTF-8 and decodes into valid UTF-8 text. An encoded image can be valid Base64 yet unsuitable for this text decoder.
The base64url variant used in some URLs differs from standard Base64. Do not randomly add or remove characters to force acceptance; establish which variant the source expects.
References: RFC 4648 — Base encodings, padding and security considerations
Example: letter count does not determine encoded size
Hi! occupies 3 UTF-8 bytes and becomes SGkh: four characters with no padding. Decoding restores the same text without a password.
The Arabic word مرحبا has 5 letters but 10 UTF-8 bytes. Its encoding is 2YXYsdit2KjYpw==, containing 16 characters. The size follows the bytes; the two = signs do not mean two original letters were removed.