What is Base64?

Base64 is a way to represent binary data using only 64 safe ASCII characters: A–Z, a–z, 0–9, + and / (with = as padding). It exists because many channels — email, JSON, URLs, XML — were designed for text and mangle raw bytes. Base64 smuggles any file through a text-only pipe intact.

How it works

Every 3 bytes (24 bits) of input are split into four 6-bit chunks, and each 6-bit value (0–63) maps to one character of the alphabet. Three bytes in, four characters out — which is why Base64 output is always about 33% larger than the original. When input length isn't divisible by 3, = padding fills the final group.

Where you meet it every day

• Data URIs — data:image/png;base64,iVBOR… embeds an image directly in HTML or CSS, saving an HTTP request.
• Email attachments — MIME encodes every attachment as Base64 text.
• JWTs — the header and payload are Base64URL-encoded JSON.
• API payloads — binary blobs inside JSON have no other standard representation.
• Basic auth — the Authorization: Basic header is Base64 of user:password.

The two classic mistakes

• Thinking it's encryption. Base64 is an encoding — fully reversible by anyone, no key involved. Never use it to "protect" secrets.
• Breaking Unicode. JavaScript's raw btoa() throws on characters outside Latin-1 — accents, CJK, emoji. The fix is encoding the string as UTF-8 bytes first, which is exactly what our converter does.

Base64 vs Base64URL

Standard Base64 uses + and /, which clash with URL syntax. Base64URL swaps them for - and _ and usually drops padding — that's the variant JWTs use.

Try it

The Base64 Fast converter encodes and decodes as you type, handles Unicode correctly, and turns any file or image into a ready-to-paste data URI — all without your data leaving the browser.