Base64 Encoder / Decoder

How Base64 Encoder / Decoder Works

What is Base64?

Base64 is a binary-to-text encoding scheme that represents any data as a string using only 64 printable ASCII characters (A–Z, a–z, 0–9, +, /, with = as padding). It exists because many systems — email (MIME), URLs, JSON, XML, HTTP headers — were designed to carry text safely but not arbitrary binary bytes. Base64 lets binary or special-character data travel through those text-only channels without corruption.

Base64 is encoding, not encryption. It is fully and trivially reversible by anyone — it provides zero confidentiality. Never use Base64 to "hide" or "protect" sensitive data; use real encryption for that.

How Base64 Encoding Works

Base64 groups input bytes into chunks of 3 (24 bits) and re-slices them into four 6-bit groups, each mapped to one of 64 characters. Because 6 bits can represent only 64 values, and each output character carries 6 bits instead of a byte’s 8, Base64 output is always about 33% larger than the original input. When the input length isn’t a multiple of 3, the output is padded with one or two trailing = characters to complete the final group.

Worked Example

"Hi" (2 bytes: 01001000 01101001) is padded to 3 bytes and split into four 6-bit groups, each mapped through the Base64 alphabet, producing SGk= — 4 characters for 2 bytes of input, with one padding character marking the incomplete final group.

Common Uses of Base64

• Email attachments (MIME): binary files are Base64-encoded so they survive text-only SMTP transport.
• Data URIs: small images/fonts embedded directly in CSS or HTML as data:image/png;base64,..., avoiding an extra HTTP request.
• JWT tokens: the header and payload of every JSON Web Token are Base64URL-encoded (a URL-safe variant using -/_ instead of +//, and normally omitting padding).
• Basic Auth headers: HTTP Authorization: Basic <base64(user:pass)>.
• Storing binary in JSON/XML: both formats are text-only, so binary payloads (images, keys, certificates) are Base64-encoded to fit inside a string field — see the JSON Formatter for inspecting the result.

Base64 vs Base64URL

This tool encodes and decodes standard Base64. If you're working with a JWT specifically, use the dedicated JWT Decoder, which handles the Base64URL variant and parses the claims automatically.

Common Mistakes

• Treating Base64 as encryption. Anyone can decode it instantly — it adds no security whatsoever.
• Forgetting the ~33% size increase. A 3 MB file becomes roughly 4 MB once Base64-encoded — relevant when embedding assets or hitting payload size limits.
• Mixing up Base64 and Base64URL. A JWT segment won't decode correctly with a standard Base64 decoder if it contains - or _ characters.
• Assuming decode always succeeds. Not every string is valid Base64 — this tool reports invalid input as a clear result rather than a cryptic error.
• Losing padding when copying. Some systems strip trailing = characters; this decoder restores missing padding automatically, but not every decoder does.

Privacy

Encoding and decoding run entirely in your browser via JavaScript — text never leaves your machine while you type. If JavaScript is disabled, the form falls back to a transient server-side computation that is not stored or logged. Input is capped at 1 MB.